# Apache NiFi Registry System Administrator’s Guide

Apache NiFi Team
dev@nifi.apache.org

## System Requirements

NiFi Registry has the following minimum system requirements:

- Requires Java 21

| When running Registry with only a JRE you may encounter the following error as Flyway (database migration tool) attempts to utilize a resource from the JDK: `java.lang.RuntimeException: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'flywayInitializer' defined in class path resource [org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration$FlywayConfiguration.class]: Invocation of init method failed; nested exception is org.flywaydb.core.api.FlywayException: Validate failed: Detected failed migration to version 1.3 (DropBucketItemNameUniqueness)`

- Supported Operating Systems:

  - Linux

  - Unix

  - Mac OS X

- Supported Web Browsers:

  - Google Chrome: Current & (Current - 1)

  - Mozilla FireFox: Current & (Current - 1)

  - Safari: Current & (Current - 1)

## How to install and start NiFi Registry

- Linux/Unix/OS X

  - Decompress and untar into desired installation directory

  - Make any desired edits in files found under `<installdir>/conf`

  - From the `<installdir>/bin` directory, execute the following commands by typing `./nifi-registry.sh <command>`:

    - `start`: starts NiFi Registry in the background

    - `stop`: stops NiFi Registry that is running in the background

    - `status`: provides the current status of NiFi Registry

    - `run`: runs NiFi Registry in the foreground and waits for a Ctrl-C to initiate shutdown of NiFi Registry

    - `install`: installs NiFi Registry as a service that can then be controlled via

      - `service nifi-registry start`

      - `service nifi-registry stop`

      - `service nifi-registry status`

When NiFi Registry first starts up, the following directories are created:

- `flow_storage`

- `database`

- `work`

- `logs`

- `run`

See the System Properties section of this guide for more information about NiFi Registry configuration files.

## Recommended Antivirus Exclusions

Antivirus software can take a long time to scan large directories and the numerous files within them. Additionally, if the antivirus software locks files or directories during a scan, those resources are unavailable to NiFi Registry processes, causing latency or unavailability of these resources in a NiFi Registry instance. To prevent these performance and reliability issues from occurring, it is highly recommended to configure your antivirus software to skip scans on the following NiFi Registry directories:

- `database`

- `extension_bundles`

- `flow_storage`

- `logs`

| The directories listed are generated at startup for a default NiFi Registry installation. Consider your configuration when determining directories to exclude during antivirus scans. For example, if an external database has been setup or if a different flow storage directory is specified in your configuration.

## Security Configuration

NiFi Registry provides several different configuration options for security purposes. The most important properties are those under the "security properties" heading in the nifi-registry.properties file. In order to run securely, the following properties must be set:

Property Name | Description
--- | ---
`nifi.registry.security.keystore` | Filename of the Keystore that contains the server’s private key.
`nifi.registry.security.keystoreType` | The type of Keystore. Must be `PKCS12` or `JKS` or `BCFKS`. JKS is the preferred type, BCFKS and PKCS12 files will be loaded with BouncyCastle provider.
`nifi.registry.security.keystorePasswd` | The password for the Keystore.
`nifi.registry.security.keyPasswd` | The password for the certificate in the Keystore. If not set, the value of `nifi.registry.security.keystorePasswd` will be used.
`nifi.registry.security.truststore` | Filename of the Truststore that will be used to authorize those connecting to NiFi Registry. A secured instance with no Truststore will refuse all incoming connections.
`nifi.registry.security.truststoreType` | The type of the Truststore. Must be `PKCS12` or `JKS` or `BCFKS`. JKS is the preferred type, BCFKS and PKCS12 files will be loaded with BouncyCastle provider.
`nifi.registry.security.truststorePasswd` | The password for the Truststore.
`nifi.registry.security.needClientAuth` | This specifies that connecting clients must authenticate with a client cert. Setting this to `false` will specify that connecting clients may optionally authenticate with a client cert, but may also login with a username and password against a configured identity provider. The default value is `true`.

Once the above properties have been configured, we can enable the User Interface to be accessed over HTTPS instead of HTTP. This is accomplished by setting the `nifi.registry.web.https.host` and `nifi.registry.web.https.port` properties. The `nifi.registry.web.https.host` property indicates which hostname the server should run on. If it is desired that the HTTPS interface be accessible from all network interfaces, a value of `0.0.0.0` should be used for `nifi.registry.web.https.host`.

| It is important when enabling HTTPS that the `nifi.registry.web.http.port` property be unset.

### TLS Cipher Suites

The Java Runtime Environment provides the ability to specify custom TLS cipher suites to be used by servers when accepting client connections. See here for more information. To use this feature for the NiFi web service, the following NiFi properties may be set:

Property Name | Description
--- | ---
`nifi.registry.web.https.ciphersuites.include` | Set of ciphers that are available to be used by incoming client connections. Replaces system defaults if set.
`nifi.registry.web.https.ciphersuites.exclude` | Set of ciphers that must not be used by incoming client connections. Filters available ciphers if set.

Each property should take the form of a comma-separated list of common cipher names as specified here. Regular expressions (for example `^.*GCM_SHA256$`) may also be specified.

The semantics match the use of the following Jetty APIs:

- SslContextFactory.setIncludeCipherSuites()

- SslContextFactory.setExcludeCipherSuites()

## User Authentication

A secured instance of NiFi Registry cannot be accessed anonymously, so a method of user authentication must be configured.

| NiFi Registry does not perform user authentication over HTTP. Using HTTP, all users will have full permissions.

Any secured instance of NiFi Registry supports authentication via client certificates that are trusted by the NiFi Registry’s SSL Context Truststore. Alternatively, a secured NiFi Registry can be configured to authenticate users via username/password.

Username/password authentication is performed by an 'Identity Provider'. The Identity Provider is a pluggable mechanism for authenticating users via their username/password. Which Identity Provider to use is configured in the nifi-registry.properties file. Currently NiFi Registry offers Identity Providers for LDAP and Kerberos.

Identity Providers are configured using two properties in the nifi-registry.properties file:

- The `nifi.registry.security.identity.providers.configuration.file` property specifies the configuration file where identity providers are defined. By default, the identity-providers.xml file located in the root installation `conf` directory is selected.

- The `nifi.registry.security.identity.provider` property indicates which of the configured identity providers in the identity-providers.xml file to use. By default, this property is not configured meaning that username/password must be explicitly enabled.

| NiFi Registry can only be configured to use one Identity Provider at a given time.

### Lightweight Directory Access Protocol (LDAP)

Below is an example and description of configuring a Identity Provider that integrates with a Directory Server to authenticate users.

Set the following in nifi-registry.properties to enable LDAP username/password authentication:

    nifi.registry.security.identity.provider=ldap-identity-provider

Modify identity-providers.xml to enable the `ldap-identity-provider`. Here is the sample provided in the file:

    <provider>
        <identifier>ldap-identity-provider</identifier>
        <class>org.apache.nifi.registry.security.ldap.LdapIdentityProvider</class>
        <property name="Authentication Strategy">START_TLS</property>

        <property name="Manager DN"></property>
        <property name="Manager Password"></property>

        <property name="TLS - Keystore"></property>
        <property name="TLS - Keystore Password"></property>
        <property name="TLS - Keystore Type"></property>
        <property name="TLS - Truststore"></property>
        <property name="TLS - Truststore Password"></property>
        <property name="TLS - Truststore Type"></property>
        <property name="TLS - Client Auth"></property>
        <property name="TLS - Protocol"></property>
        <property name="TLS - Shutdown Gracefully"></property>

        <property name="Referral Strategy">FOLLOW</property>
        <property name="Connect Timeout">10 secs</property>
        <property name="Read Timeout">10 secs</property>

        <property name="Url"></property>
        <property name="User Search Base"></property>
        <property name="User Search Filter"></property>

        <property name="Identity Strategy">USE_DN</property>
        <property name="Authentication Expiration">12 hours</property>
    </provider>

The `ldap-identity-provider` has the following properties:

Property Name | Description
--- | ---
`Authentication Strategy` | How the connection to the LDAP server is authenticated. Possible values are `ANONYMOUS`, `SIMPLE`, `LDAPS`, or `START_TLS`.
`Manager DN` | The DN of the manager that is used to bind to the LDAP server to search for users.
`Manager Password` | The password of the manager that is used to bind to the LDAP server to search for users.
`TLS - Keystore` | Path to the Keystore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Keystore Password` | Password for the Keystore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Keystore Type` | Type of the Keystore that is used when connecting to LDAP using LDAPS or START_TLS (i.e. `JKS` or `PKCS12`).
`TLS - Truststore` | Path to the Truststore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Truststore Password` | Password for the Truststore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Truststore Type` | Type of the Truststore that is used when connecting to LDAP using LDAPS or START_TLS (i.e. `JKS` or `PKCS12`).
`TLS - Client Auth` | Client authentication policy when connecting to LDAP using LDAPS or START_TLS. Possible values are `REQUIRED`, `WANT`, `NONE`.
`TLS - Protocol` | Protocol to use when connecting to LDAP using LDAPS or START_TLS. (i.e. `TLS`, `TLSv1.1`, `TLSv1.2`, etc).
`TLS - Shutdown Gracefully` | Specifies whether the TLS should be shut down gracefully before the target context is closed. Defaults to `false`.
`Referral Strategy` | Strategy for handling referrals. Possible values are `FOLLOW`, `IGNORE`, `THROW`.
`Connect Timeout` | Duration of connect timeout. (i.e. `10 secs`).
`Read Timeout` | Duration of read timeout. (i.e. `10 secs`).
`Url` | Space-separated list of URLs of the LDAP servers (i.e. `ldap://<hostname>:<port>`).
`User Search Base` | Base DN for searching for users (i.e. `CN=Users,DC=example,DC=com`).
`User Search Filter` | Filter for searching for users against the `User Search Base`. (i.e. `sAMAccountName={0}`). The user specified name is inserted into '{0}'.
`Identity Strategy` | Strategy to identify users. Possible values are `USE_DN` and `USE_USERNAME`. The default functionality if this property is missing is `USE_DN` in order to retain backward compatibility. `USE_DN` will use the full DN of the user entry if possible. `USE_USERNAME` will use the username the user logged in with.
`Authentication Expiration` | The duration of how long the user authentication is valid for. If the user never logs out, they will be required to log back in following this duration.

### Kerberos

Below is an example and description of configuring an Identity Provider that integrates with a Kerberos Key Distribution Center (KDC) to authenticate users.

Set the following in nifi-registry.properties to enable Kerberos username/password authentication:

    nifi.registry.security.user.identity.provider=kerberos-identity-provider

Modify identity-providers.xml to enable the `kerberos-identity-provider`. Here is the sample provided in the file:

    <provider>
        <identifier>kerberos-identity-provider</identifier>
        <class>org.apache.nifi.registry.web.security.authentication.kerberos.KerberosIdentityProvider</class>
        <property name="Default Realm">NIFI.APACHE.ORG</property>
        <property name="Authentication Expiration">12 hours</property>
        <property name="Enable Debug">false</property>
    </provider>

The `kerberos-identity-provider` has the following properties:

Property Name | Description
--- | ---
`Default Realm` | Default realm to provide when user enters incomplete user principal (i.e. `NIFI.APACHE.ORG`).
`Authentication Expiration` | The duration for which the user authentication is valid. If the user never logs out, they will be required to log back in following this duration.
`Enable Debug` | Enables debug logging output for the SunJaasKerberosClient used internally by the KerberosIdentityProvider. By default, this is set to `false`.

See also Kerberos Service to allow single sign-on access via client Kerberos tickets.

### OpenID Connect

OpenID Connect integration provides single sign-on using a specified Authorization Server. The implementation supports the Authorization Code Grant Type as described in RFC 6749 Section 4.1 and OpenID Connect Core Section 3.1.1.

The implementation enables OpenID Connect RP-Initiated Logout 1.0 when the Authorization Server includes an `end_session_endpoint` element in the OpenID Discovery configuration.

OpenID Connect integration supports the following settings in nifi-registry.properties.

Property Name | Description
--- | ---
`nifi.registry.security.user.oidc.discovery.url` | The Discovery Configuration URL for the OpenID Connect Provider
`nifi.registry.security.user.oidc.connect.timeout` | Socket Connect timeout when communicating with the OpenID Connect Provider. The default value is `5 secs`
`nifi.registry.security.user.oidc.read.timeout` | Socket Read timeout when communicating with the OpenID Connect Provider. The default value is `5 secs`
`nifi.registry.security.user.oidc.client.id` | The Client ID for NiFi Registry registered with the OpenID Connect Provider
`nifi.registry.security.user.oidc.client.secret` | The Client Secret for NiFi Registry registered with the OpenID Connect Provider
`nifi.registry.security.user.oidc.preferred.jwsalgorithm` | The preferred algorithm for validating identity tokens. If this value is blank, it will default to `RS256` which is required to be supported by the OpenID Connect Provider according to the specification. If this value is `HS256`, `HS384`, or `HS512`, NiFi Registry will attempt to validate HMAC protected tokens using the specified client secret. If this value is `none`, NiFi will attempt to validate unsecured/plain tokens. Other values for this algorithm will attempt to parse as an RSA or EC algorithm to be used in conjunction with the JSON Web Key (JWK) provided through the jwks_uri in the metadata found at the discovery URL
`nifi.registry.security.user.oidc.additional.scopes` | Comma separated scopes that are sent to OpenID Connect Provider in addition to `openid` and `email`.
`nifi.registry.security.user.oidc.claim.identifying.user` | Claim that identifies the authenticated user. The default value is `email`. Claim names may need to be requested using the `nifi.registry.security.user.oidc.additional.scopes` property

## Authorization

After you have configured NiFi Registry to run securely and with an authentication mechanism, you must configure who has access to the system and their level of access. This is done by defining policies that give users and groups permissions to perform a particular action. These policies are defined in an 'authorizer'.

### Authorizer Configuration

An 'authorizer' manages known users and their access policies. Authorizers are configured using two properties in the nifi-registry.properties file:

- The `nifi.registry.security.authorizers.configuration.file` property specifies the configuration file where authorizers are defined. By default, the authorizers.xml file located in the root installation conf directory is selected.

- The `nifi.registry.security.authorizer` property indicates which of the configured authorizers in the authorizers.xml file to use.

### Authorizers.xml Setup

The authorizers.xml file is used to define and configure available authorizers.

#### StandardManagedAuthorizer

The default Authorizer is the StandardManagedAuthorizer, however, you can develop additional Authorizers as extensions. The StandardManagedAuthorizer has the following properties:

Property Name | Description
--- | ---
`Access Policy Provider` | The identifier for an Access Policy Provider defined above.

The managed authorizer is comprised of a UserGroupProvider and a AccessPolicyProvider. The users, group, and access policies will be loaded and optionally configured through these providers. The managed authorizer will make all access decisions based on these provided users, groups, and access policies.

During startup there is a check to ensure that there are no two users/groups with the same identity/name. This check is executed regardless of the configured implementation. This is necessary because this is how users/groups are identified and authorized during access decisions.

#### UserGroupProvider

##### FileUserGroupProvider

The default UserGroupProvider is the FileUserGroupProvider, however, you can develop additional UserGroupProviders as extensions. The FileUserGroupProvider has the following properties:

Property Name | Description
--- | ---
`Users File` | The file where the FileUserGroupProvider stores users and groups. By default, users.xml in the `conf` directory is chosen.
`Initial User Identity` | The identity of a user or system to seed an empty Users File. Multiple Initial User Identity properties can be specified, but the name of each property must be unique, for example: `"Initial User Identity A"`, `"Initial User Identity B"`, `"Initial User Identity C"` or `"Initial User Identity 1"`, `"Initial User Identity 2"`, `"Initial User Identity 3"`.

| Initial User Identities are only created if the specified Users File is missing or empty during NiFi Registry startup. Changes to the configured Initial Users Identities will not take effect if the Users File is populated.

##### LdapUserGroupProvider

Another option for the UserGroupProvider is the LdapUserGroupProvider. By default, this option is commented out but can be configured in lieu of the FileUserGroupProvider. This will sync users and groups from a directory server and will present them in NiFi Registry UI in read only form. The LdapUserGroupProvider has the following properties:

Property Name | Description
--- | ---
`Authentication Strategy` | How the connection to the LDAP server is authenticated. Possible values are `ANONYMOUS`, `SIMPLE`, `LDAPS`, or `START_TLS`.
`Manager DN` | The DN of the manager that is used to bind to the LDAP server to search for users.
`Manager Password` | The password of the manager that is used to bind to the LDAP server to search for users.
`TLS - Keystore` | Path to the Keystore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Keystore Password` | Password for the Keystore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Keystore Type` | Type of the Keystore that is used when connecting to LDAP using LDAPS or START_TLS (i.e. `JKS` or `PKCS12`).
`TLS - Truststore` | Path to the Truststore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Truststore Password` | Password for the Truststore that is used when connecting to LDAP using LDAPS or START_TLS.
`TLS - Truststore Type` | Type of the Truststore that is used when connecting to LDAP using LDAPS or START_TLS (i.e. `JKS` or `PKCS12`).
`TLS - Client Auth` | Client authentication policy when connecting to LDAP using LDAPS or START_TLS. Possible values are `REQUIRED`, `WANT`, `NONE`.
`TLS - Protocol` | Protocol to use when connecting to LDAP using LDAPS or START_TLS. (i.e. `TLS`, `TLSv1.1`, `TLSv1.2`, etc).
`TLS - Shutdown Gracefully` | Specifies whether the TLS should be shut down gracefully before the target context is closed. Defaults to `false`.
`Referral Strategy` | Strategy for handling referrals. Possible values are `FOLLOW`, `IGNORE`, `THROW`.
`Connect Timeout` | Duration of connect timeout. (i.e. `10 secs`).
`Read Timeout` | Duration of read timeout. (i.e. `10 secs`).
`Url` | Space-separated list of URLs of the LDAP servers (i.e. `ldap://<hostname>:<port>`).
`Page Size` | Sets the page size when retrieving users and groups. If not specified, no paging is performed.
`Sync Interval` | Duration of time between syncing users and groups. (i.e. `30 mins`).
`Group Membership - Enforce Case Sensitivity` | Sets whether group membership decisions are case sensitive. When a user or group is inferred (by not specifying or user or group search base or user identity attribute or group name attribute) case sensitivity is enforced since the value to use for the user identity or group name would be ambiguous. Defaults to false.
`User Search Base` | Base DN for searching for users (i.e. `ou=users,o=nifi`). Required to search users.
`User Object Class` | Object class for identifying users (i.e. `person`). Required if searching users.
`User Search Scope` | Search scope for searching users (`ONE_LEVEL`, `OBJECT`, or `SUBTREE`). Required if searching users.
`User Search Filter` | Filter for searching for users against the `User Search Base` (i.e. `(memberof=cn=team1,ou=groups,o=nifi)`). Optional.
`User Identity Attribute` | Attribute to use to extract user identity (i.e. `cn`). Optional. If not set, the entire DN is used.
`User Group Name Attribute` | Attribute to use to define group membership (i.e. `memberof`). Optional. If not set group membership will not be calculated through the users. Will rely on group membership being defined through `Group Member Attribute` if set. The value of this property is the name of the attribute in the user LDAP entry that associates them with a group. The value of that user attribute could be a dn or group name for instance. What value is expected is configured in the `User Group Name Attribute - Referenced Group Attribute`.
`User Group Name Attribute - Referenced Group Attribute` | If blank, the value of the attribute defined in `User Group Name Attribute` is expected to be the full dn of the group. If not blank, this property will define the attribute of the group LDAP entry that the value of the attribute defined in `User Group Name Attribute` is referencing (i.e. `name`). Use of this property requires that `Group Search Base` is also configured.
`Group Search Base` | Base DN for searching for groups (i.e. `ou=groups,o=nifi`). Required to search groups.
`Group Object Class` | Object class for identifying groups (i.e. `groupOfNames`). Required if searching groups.
`Group Search Scope` | Search scope for searching groups (`ONE_LEVEL`, `OBJECT`, or `SUBTREE`). Required if searching groups.
`Group Search Filter` | Filter for searching for groups against the `Group Search Base`. Optional.
`Group Name Attribute` | Attribute to use to extract group name (i.e. `cn`). Optional. If not set, the entire DN is used.
`Group Member Attribute` | Attribute to use to define group membership (i.e. `member`). Optional. If not set group membership will not be calculated through the groups. Will rely on group membership being defined through `User Group Name Attribute` if set. The value of this property is the name of the attribute in the group LDAP entry that associates them with a user. The value of that group attribute could be a dn or memberUid for instance. What value is expected is configured in the `Group Member Attribute - Referenced User Attribute`. (i.e. `member: cn=User 1,ou=users,o=nifi` vs. `memberUid: user1`)
`Group Member Attribute - Referenced User Attribute` | If blank, the value of the attribute defined in `Group Member Attribute` is expected to be the full dn of the user. If not blank, this property will define the attribute of the user LDAP entry that the value of the attribute defined in `Group Member Attribute` is referencing (i.e. `uid`). Use of this property requires that `User Search Base` is also configured. (i.e. `member: cn=User 1,ou=users,o=nifi` vs. `memberUid: user1`)

##### Composite Implementations

Another option for the UserGroupProvider are composite implementations. This means that multiple sources/implementations can be configured and composed. For instance, an admin can configure users/groups to be loaded from a file and a directory server. There are two composite implementations, one that supports multiple UserGroupProviders and one that supports multiple UserGroupProviders and a single configurable UserGroupProvider.

The CompositeUserGroupProvider will provide support for retrieving users and groups from multiple sources. The CompositeUserGroupProvider has the following properties:

Property Name | Description
--- | ---
`User Group Provider` | The identifier of user group providers to load from. The name of each property must be unique, for example: `"User Group Provider A"`, `"User Group Provider B"`, `"User Group Provider C"` or `"User Group Provider 1"`, `"User Group Provider 2"`, `"User Group Provider 3"`

The CompositeConfigurableUserGroupProvider will provide support for retrieving users and groups from multiple sources. Additionally, a single configurable user group provider is required. Users from the configurable user group provider are configurable, however users loaded from one of the User Group Provider [unique key] will not be. The CompositeConfigurableUserGroupProvider has the following properties:

Property Name | Description
--- | ---
`Configurable User Group Provider` | A configurable user group provider.
`User Group Provider` | The identifier of user group providers to load from. The name of each property must be unique, for example: `"User Group Provider A"`, `"User Group Provider B"`, `"User Group Provider C"` or `"User Group Provider 1"`, `"User Group Provider 2"`, `"User Group Provider 3"`

#### AccessPolicyProvider

After you have configured a UserGroupProvider, you must configure an AccessPolicyProvider that will control Access Policies for the identities in the UserGroupProvider.

##### FileAccessPolicyProvider

The default AccessPolicyProvider is the FileAccessPolicyProvider, however, you can develop additional AccessPolicyProvider as extensions. The FileAccessPolicyProvider has the following properties:

Property Name | Description
--- | ---
`User Group Provider` | The identifier for an User Group Provider defined above that will be used to access users and groups for use in the managed access policies.
`Authorizations File` | The file where the FileAccessPolicyProvider will store policies. By default, authorizations.xml in the `conf` directory is chosen.
`Initial Admin Identity` | The identity of an initial admin user that will be granted access to the UI and given the ability to create additional users, groups, and policies. For example, a certificate DN, LDAP identity, or Kerberos principal.
`NiFi Identity` | The identity of a NiFi instance/node that will be accessing this registry. Each NiFi Identity will be granted permission to proxy user requests, as well as read any bucket to perform synchronization status checks.
`NiFi Group Name` | The name of the group, whose members are NiFi instance/node identities, that will be accessing this registry. The members of this group will be granted permission to proxy user requests, as well as read any bucket to perform synchronization checks.

| The identities configured in the Initial Admin Identity and NiFi Identity properties must be available in the configured User Group Provider. Initial Admin Identity and NiFi Identity properties are only read by NiFi Registry when the Authorizations File is missing or empty on startup in order to seed the initial Authorizations File. Changes to the configured Initial Admin Identity and NiFi Identities will not take effect if the Authorizations File is populated.

#### Initial Admin Identity (New NiFi Registry Instance)

If you are setting up a secured NiFi Registry instance for the first time, you must manually designate an “Initial Admin Identity” in the authorizers.xml file. This initial admin user is granted access to the UI and given the ability to create additional users, groups, and policies. The value of this property could be a certificate DN , LDAP identity (DN or username), or a Kerberos principal. If you are the NiFi Registry administrator, add yourself as the “Initial Admin Identity”.

After you have edited and saved the authorizers.xml file, restart NiFi Registry. The users.xml and authorizations.xml files will be created, and the “Initial Admin Identity” user and administrative policies are added during start up. Once NiFi Registry starts, the “Initial Admin Identity” user is able to access the UI and begin managing users, groups, and policies.

| If initial NiFi identities are not provided, they can be added through the UI at a later time by first creating a user for the given NiFi identity, and then giving that user both Proxy permissions and permission to Buckets/READ in order to read all buckets.

Some common use cases are described below.

##### File-based (LDAP Authentication)

Here is an example certificate DN entry using the name John Smith:

    <authorizers>

        <userGroupProvider>
            <identifier>file-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileUserGroupProvider</class>
            <property name="Users File">./conf/users.xml</property>
            <property name="Legacy Authorized Users File"></property>
            <property name="Initial User Identity 1">cn=John Smith,ou=people,dc=example,dc=com</property>
        </userGroupProvider>

        <accessPolicyProvider>
            <identifier>file-access-policy-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileAccessPolicyProvider</class>
            <property name="User Group Provider">file-user-group-provider</property>
            <property name="Authorizations File">./conf/authorizations.xml</property>
            <property name="Initial Admin Identity">cn=John Smith,ou=people,dc=example,dc=com</property
            <property name="NiFi Identity 1"></property>
        </accessPolicyProvider>

        <authorizer>
            <identifier>managed-authorizer</identifier>
            <class>org.apache.nifi.registry.security.authorization.StandardManagedAuthorizer</class>
            <property name="Access Policy Provider">file-access-policy-provider</property>
        </authorizer>
    </authorizers>

##### File-based (OIDC Authentication)

Here is an example as Initial User Identity called `admin` :

    <authorizers>
        <userGroupProvider>
            <identifier>file-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileUserGroupProvider</class>
            <property name="Users File">./conf/users.xml</property>
            <property name="Initial User Identity 1">admin</property>
        </userGroupProvider>

        <accessPolicyProvider>
            <identifier>file-access-policy-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileAccessPolicyProvider</class>
            <property name="User Group Provider">file-user-group-provider</property>
            <property name="Authorizations File">./conf/authorizations.xml</property>
            <property name="Initial Admin Identity">admin</property>
            <property name="NiFi Group Name"></property>
        </accessPolicyProvider>

        <authorizer>
            <identifier>managed-authorizer</identifier>
            <class>org.apache.nifi.registry.security.authorization.StandardManagedAuthorizer</class>
            <property name="Access Policy Provider">file-access-policy-provider</property>
        </authorizer>

    </authorizers>

##### File-based (Kerberos Authentication)

Here is an example Kerberos entry using the name John Smith and realm `NIFI.APACHE.ORG`:

    <authorizers>

        <userGroupProvider>
            <identifier>file-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileUserGroupProvider</class>
            <property name="Users File">./conf/users.xml</property>
            <property name="Initial User Identity 1">johnsmith@NIFI.APACHE.ORG</property>
        </userGroupProvider>

        <accessPolicyProvider>
            <identifier>file-access-policy-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileAccessPolicyProvider</class>
            <property name="User Group Provider">file-user-group-provider</property>
            <property name="Authorizations File">./conf/authorizations.xml</property>
            <property name="Initial Admin Identity">johnsmith@NIFI.APACHE.ORG</property>
            <property name="NiFi Identity 1"></property>
        </accessPolicyProvider>

        <authorizer>
            <identifier>managed-authorizer</identifier>
            <class>org.apache.nifi.registry.security.authorization.StandardManagedAuthorizer</class>
            <property name="Access Policy Provider">file-access-policy-provider</property>
        </authorizer>
    </authorizers>

##### LDAP-based Users/Groups Referencing User DN

Here is an example loading users and groups from LDAP. Group membership will be driven through the member attribute of each group. Authorization will still use file-based access policies.

Given the following LDAP entries exist:

    dn: cn=User 1,ou=users,o=nifi
    objectClass: organizationalPerson
    objectClass: person
    objectClass: inetOrgPerson
    objectClass: top
    cn: User 1
    sn: User1
    uid: user1

    dn: cn=User 2,ou=users,o=nifi
    objectClass: organizationalPerson
    objectClass: person
    objectClass: inetOrgPerson
    objectClass: top
    cn: User 2
    sn: User2
    uid: user2

    dn: cn=users,ou=groups,o=nifi
    objectClass: groupOfNames
    objectClass: top
    cn: users
    member: cn=User 1,ou=users,o=nifi
    member: cn=User 2,ou=users,o=nifi

An Authorizer using an LdapUserGroupProvider would be configured as:

    <authorizers>
        <userGroupProvider>
            <identifier>ldap-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.ldap.tenants.LdapUserGroupProvider</class>
            <property name="Authentication Strategy">ANONYMOUS</property>

            <property name="Manager DN"></property>
            <property name="Manager Password"></property>

            <property name="TLS - Keystore"></property>
            <property name="TLS - Keystore Password"></property>
            <property name="TLS - Keystore Type"></property>
            <property name="TLS - Truststore"></property>
            <property name="TLS - Truststore Password"></property>
            <property name="TLS - Truststore Type"></property>
            <property name="TLS - Client Auth"></property>
            <property name="TLS - Protocol"></property>
            <property name="TLS - Shutdown Gracefully"></property>

            <property name="Referral Strategy">FOLLOW</property>
            <property name="Connect Timeout">10 secs</property>
            <property name="Read Timeout">10 secs</property>

            <property name="Url">ldap://localhost:10389</property>
            <property name="Page Size"></property>
            <property name="Sync Interval">30 mins</property>
            <property name="Group Membership - Enforce Case Sensitivity">false</property>

            <property name="User Search Base">ou=users,o=nifi</property>
            <property name="User Object Class">person</property>
            <property name="User Search Scope">ONE_LEVEL</property>
            <property name="User Search Filter"></property>
            <property name="User Identity Attribute">cn</property>
            <property name="User Group Name Attribute"></property>
            <property name="User Group Name Attribute - Referenced Group Attribute"></property>

            <property name="Group Search Base">ou=groups,o=nifi</property>
            <property name="Group Object Class">groupOfNames</property>
            <property name="Group Search Scope">ONE_LEVEL</property>
            <property name="Group Search Filter"></property>
            <property name="Group Name Attribute">cn</property>
            <property name="Group Member Attribute">member</property>
            <property name="Group Member Attribute - Referenced User Attribute"></property>
        </userGroupProvider>

        <accessPolicyProvider>
            <identifier>file-access-policy-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileAccessPolicyProvider</class>
            <property name="User Group Provider">ldap-user-group-provider</property>
            <property name="Authorizations File">./conf/authorizations.xml</property>
            <property name="Initial Admin Identity">User 1</property>
            <property name="NiFi Identity 1"></property>
        </accessPolicyProvider>

        <authorizer>
            <identifier>managed-authorizer</identifier>
            <class>org.apache.nifi.registry.security.authorization.StandardManagedAuthorizer</class>
            <property name="Access Policy Provider">file-access-policy-provider</property>
        </authorizer>
    </authorizers>

The `Initial Admin Identity` value would have loaded from the cn of the User 1 entry based on the `User Identity Attribute` value.

##### Composite - File and LDAP-based Users/Groups

Here is an example composite implementation loading users and groups from LDAP and a local file. Group membership will be driven through the member attribute of each group. The users from LDAP will be read only while the users loaded from the file will be configurable in UI.

    <authorizers>

        <userGroupProvider>
            <identifier>file-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileUserGroupProvider</class>
            <property name="Users File">./conf/users.xml</property>
            <property name="Initial User Identity 1">cn=nifi-node1,ou=servers,dc=example,dc=com</property>
            <property name="Initial User Identity 2">cn=nifi-node2,ou=servers,dc=example,dc=com</property>
        </userGroupProvider>

        <userGroupProvider>
            <identifier>ldap-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.ldap.tenants.LdapUserGroupProvider</class>
            <property name="Authentication Strategy">ANONYMOUS</property>

            <property name="Manager DN"></property>
            <property name="Manager Password"></property>

            <property name="TLS - Keystore"></property>
            <property name="TLS - Keystore Password"></property>
            <property name="TLS - Keystore Type"></property>
            <property name="TLS - Truststore"></property>
            <property name="TLS - Truststore Password"></property>
            <property name="TLS - Truststore Type"></property>
            <property name="TLS - Client Auth"></property>
            <property name="TLS - Protocol"></property>
            <property name="TLS - Shutdown Gracefully"></property>

            <property name="Referral Strategy">FOLLOW</property>
            <property name="Connect Timeout">10 secs</property>
            <property name="Read Timeout">10 secs</property>

            <property name="Url">ldap://localhost:10389</property>
            <property name="Page Size"></property>
            <property name="Sync Interval">30 mins</property>
            <property name="Group Membership - Enforce Case Sensitivity">false</property>

            <property name="User Search Base">ou=users,o=nifi</property>
            <property name="User Object Class">person</property>
            <property name="User Search Scope">ONE_LEVEL</property>
            <property name="User Search Filter"></property>
            <property name="User Identity Attribute">cn</property>
            <property name="User Group Name Attribute"></property>
            <property name="User Group Name Attribute - Referenced Group Attribute"></property>

            <property name="Group Search Base">ou=groups,o=nifi</property>
            <property name="Group Object Class">groupOfNames</property>
            <property name="Group Search Scope">ONE_LEVEL</property>
            <property name="Group Search Filter"></property>
            <property name="Group Name Attribute">cn</property>
            <property name="Group Member Attribute">member</property>
            <property name="Group Member Attribute - Referenced User Attribute"></property>
        </userGroupProvider>

        <userGroupProvider>
            <identifier>composite-user-group-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.CompositeUserGroupProvider</class>
            <property name="User Group Provider 1">file-user-group-provider</property>
            <property name="User Group Provider 2">ldap-user-group-provider</property>
        </userGroupProvider>

        <accessPolicyProvider>
            <identifier>file-access-policy-provider</identifier>
            <class>org.apache.nifi.registry.security.authorization.file.FileAccessPolicyProvider</class>
            <property name="User Group Provider">composite-user-group-provider</property>
            <property name="Authorizations File">./conf/authorizations.xml</property>
            <property name="Initial Admin Identity">User 1/property>
            <property name="NiFi Identity 1">cn=nifi-node1,ou=servers,dc=example,dc=com</property>
            <property name="NiFi Identity 2">cn=nifi-node2,ou=servers,dc=example,dc=com</property>
        </accessPolicyProvider>

        <authorizer>
            <identifier>managed-authorizer</identifier>
            <class>org.apache.nifi.registry.security.authorization.StandardManagedAuthorizer</class>
            <property name="Access Policy Provider">file-access-policy-provider</property>
        </authorizer>
    </authorizers>

In this example, the users and groups are loaded from LDAP but the servers are managed in a local file. The `Initial Admin Identity` value came from an attribute in a LDAP entry based on the `User Identity Attribute`. The `NiFi Identity` values are established in the local file using the `Initial User Identity` properties.

### Access Policies

You can manage the ability for users and groups to view or modify NiFi Registry resources using 'access policies'. Access policies can be created to control access to buckets, as well as to grant special privileges to users for managing a NiFi Registry instance.

#### Bucket Policies

Bucket policies govern the following bucket level authorizations:

Policy | Privilege | Resource Descriptor
--- | --- | ---
Read Bucket | Allows users to read items in the bucket | `resource="/buckets/<bucket-UUID>" action="R"`
Write Bucket | Allows users to write items to the bucket | `resource="/buckets/<bucket-UUID>" action="W"`
Delete Bucket | Allows users to delete the bucket | `resource="/buckets/<bucket-UUID>" action="D"`

#### Special Privilege Policies

Special privilege policies govern the following system level authorizations:

Policy | Privilege | Resource Descriptor
--- | --- | ---
Can Manage Buckets (Read) | Allows users to read from all buckets | `resource="/buckets" action="R"`
Can Manage Buckets (Write) | Allows users to write to all buckets | `resource="/buckets" action="W"`
Can Manage Buckets (Delete) | Allows users to delete all buckets | `resource="/buckets" action="D"`
Can Manage Users (Read) | Allows users to view users | `resource="/tenants" action="R"`
Can Manage Users (Write) | Allows users to create and modify users | `resource="/tenants" action="W"`
Can Manage Users (Delete) | Allows users to delete users | `resource="/tenants" action="D"`
Can Manage Policies (Read) | Allows users to view policies | `resource="/policies" action="R"`
Can Manage Policies (Write) | Allows users to create and modify policies | `resource="/policies" action="W"`
Can Manage Policies (Delete) | Allows users to delete policies | `resource="/policies" action="D"`
Can Proxy Requests (Read) | Allows users to proxy read requests (GET) | `resource="/proxy" action="R"`
Can Proxy Requests (Write) | Allows users to proxy write requests (POST, PUT, PATCH) | `resource="/proxy" action="W"`
Can Proxy Requests (Delete) | Allows users to proxy delete requests (DELETE) | `resource="/proxy" action="D"`
View Swagger | Allows users to access the self-hosted Swagger UI | `resource="/swagger" action="R"`
View Actuator | Allows users to access the Spring Boot Actuator end-points | `resource="/actuator" action="R"`

## Encrypted Passwords in Configuration Files

In order to facilitate the secure setup of NiFi Registry, you can use the `encrypt-config` command line utility to encrypt raw configuration values that NiFi Registry decrypts in memory on startup. This extensible protection scheme transparently allows NiFi Registry to use raw values in operation, while protecting them at rest. In the future, hardware security modules (HSM) and external secure storage mechanisms will be integrated, but for now, an AES encryption provider is the default implementation.

If no administrator action is taken, the configuration values remain unencrypted.

| The `encrypt-config` tool for NiFi Registry is implemented as an additional mode to the existing tool in the `nifi-toolkit`. The following sections assume you have downloaded the binary for the nifi-toolkit.

### Encrypt-Config Tool

The `encrypt-config` command line tool can be used to encrypt NiFi Registry configuration by invoking the tool with the following command:

    ./bin/encrypt-config --nifiRegistry [options]

You can use the following command line options with the `encrypt-config` tool:

- `-h`,`--help` Show usage information (this message)

- `-v`,`--verbose` Sets verbose mode (default false)

- `-p`,`--password <password>` Protect the files using a password-derived key. If an argument is not provided to this flag, interactive mode will be triggered to prompt the user to enter the password.

- `-k`,`--key <keyhex>` Protect the files using a raw hexadecimal key. If an argument is not provided to this flag, interactive mode will be triggered to prompt the user to enter the key.

- `--oldPassword <password>` If the input files are already protected using a password-derived key, this specifies the old password so that the files can be unprotected before re-protecting.

- `--oldKey <keyhex>` If the input files are already protected using a key, this specifies the raw hexadecimal key so that the files can be unprotected before re-protecting.

- `-b`,`--bootstrapConf <file>` The bootstrap.conf file containing no root key or an existing root key. If a new password or key is specified (using `-p` or `-k`) and no output bootstrap.conf file is specified, then this file will be overwritten to persist the new root key.

- `-B`,`--outputBootstrapConf <file>` The destination bootstrap.conf file to persist root key. If specified, the input bootstrap.conf will not be modified.

- `-r`,`--nifiRegistryProperties <file>` The nifi-registry.properties file containing unprotected config values, overwritten if no output file specified.

- `-R`,`--outputNifiRegistryProperties <file>` The destination nifi-registry.properties file containing protected config values.

- `-a`,`--authorizersXml <file>` The authorizers.xml file containing unprotected config values, overwritten if no output file specified.

- `-A`,`--outputAuthorizersXml <file>` The destination authorizers.xml file containing protected config values.

- `-i`,`--identityProvidersXml <file>` The identity-providers.xml file containing unprotected config values, overwritten if no output file specified.

- `-I`,`--outputIdentityProvidersXml <file>` The destination identity-providers.xml file containing protected config values.

- `--decrypt` Can be used with `-r` to decrypt a previously encrypted NiFi Registry Properties file. Decrypted content is printed to STDOUT.

As an example of how the tool works, assume that you have installed the tool on a machine supporting 256-bit encryption and with the following existing values in the nifi-registry.properties file:

    # security properties #
    nifi.registry.security.keystore=/path/to/keystore.jks
    nifi.registry.security.keystoreType=JKS
    nifi.registry.security.keystorePasswd=thisIsABadKeystorePassword
    nifi.registry.security.keyPasswd=thisIsABadKeyPassword
    nifi.registry.security.truststore=
    nifi.registry.security.truststoreType=
    nifi.registry.security.truststorePasswd=

Enter the following arguments when using the tool:

    ./bin/encrypt-config.sh --nifiRegistry \
    -b bootstrap.conf \
    -k 0123456789ABCDEFFEDCBA98765432100123456789ABCDEFFEDCBA9876543210 \
    -r nifi-registry.properties

As a result, the nifi-registry.properties file is overwritten with protected properties and sibling encryption identifiers (`aes/gcm/256`, the currently supported algorithm):

    # security properties #
    nifi.registry.security.keystore=/path/to/keystore.jks
    nifi.registry.security.keystoreType=JKS
    nifi.registry.security.keystorePasswd=oBjT92hIGRElIGOh||MZ6uYuWNBrOA6usq/Jt3DaD2e4otNirZDytac/w/KFe0HOkrJR03vcbo
    nifi.registry.security.keystorePasswd.protected=aes/gcm/256
    nifi.registry.security.keyPasswd=ac/BaE35SL/esLiJ||+ULRvRLYdIDA2VqpE0eQXDEMjaLBMG2kbKOdOwBk/hGebDKlVg==
    nifi.registry.security.keyPasswd.protected=aes/gcm/256
    nifi.registry.security.truststore=
    nifi.registry.security.truststoreType=
    nifi.registry.security.truststorePasswd=

When applied to identity-providers.xml or authorizers.xml, the property elements are updated with an `encryption` attribute. For example:

    <!-- LDAP Provider -->
    <provider>
       <identifier>ldap-provider</identifier>
       <class>org.apache.nifi.registry.security.ldap.LdapProvider</class>
       <property name="Authentication Strategy">START_TLS</property>
       <property name="Manager DN">someuser</property>
       <property name="Manager Password" encryption="aes/gcm/128">q4r7WIgN0MaxdAKM||SGgdCTPGSFEcuH4RraMYEdeyVbOx93abdWTVSWvh1w+klA</property>
       <property name="TLS - Keystore">/path/to/keystore.jks</property>
       <property name="TLS - Keystore Password" encryption="aes/gcm/128">Uah59TWX+Ru5GY5p||B44RT/LJtC08QWA5ehQf01JxIpf0qSJUzug25UwkF5a50g</property>
       <property name="TLS - Keystore Type">JKS</property>
       ...
    </provider>

Additionally, the bootstrap.conf file is updated with the encryption key as follows:

    # Root key in hexadecimal format for encrypted sensitive configuration values
    nifi.registry.bootstrap.sensitive.key=0123456789ABCDEFFEDCBA98765432100123456789ABCDEFFEDCBA9876543210

Sensitive configuration values are encrypted by the tool by default, however you can encrypt any additional properties, if desired. To encrypt additional properties, specify them as comma-separated values in the `nifi.registry.sensitive.props.additional.keys` property.

If the nifi-registry.properties file already has valid protected values and you wish to protect additional values using the same root key already present in your bootstrap.conf, then run the tool without specifying a new key:

    # bootstrap.conf already contains root key property
    # nifi-registy.properties has been updated for nifi.registry.sensitive.props.additional.keys=...

    ./bin/encrypt-config.sh --nifiRegistry -b bootstrap.conf -r nifi-registry.properties

### Sensitive Property Key Migration

In order to change the key used to encrypt the sensitive values, provide the new key or password using the `-k` or `-p` flags as usual, and provide the existing key or password using `--old-key` or `--old-password` respectively. This will allow the toolkit to decrypt the existing values and re-encrypt them, and update bootstrap.conf with the new key. Only one of the key or password needs to be specified for each phase (old vs. new), and any combination is sufficient:

- old key → new key

- old key → new password

- old password → new key

- old password → new password

## Bootstrap Properties

The bootstrap.conf file in the `conf` directory allows users to configure settings for how NiFi Registry should be started. This includes parameters, such as the size of the Java Heap, what Java command to run, and Java System Properties.

Here, we will address the different properties that are made available in the file. Any changes to this file will take effect only after NiFi Registry has been stopped and restarted.

Property | Description
`java` | Specifies the fully qualified java command to run. By default, it is simply `java` but could be changed to an absolute path or a reference an environment variable, such as `$JAVA_HOME/bin/java`
`run.as` | The username to run NiFi Registry as. For instance, if NiFi Registry should be run as the `nifi_registry` user, setting this value to `nifi_registry` will cause the NiFi Registry Process to be run as the `nifi_registry` user. This property is ignored on Windows. For Linux, the specified user may require sudo permissions.
`lib.dir` | The lib directory to use for NiFi Registry. By default, this is set to `./lib`
`conf.dir` | The `conf` directory to use for NiFi Registry. By default, this is set to `./conf`
`graceful.shutdown.seconds` | When NiFi Registry is instructed to shutdown, the Bootstrap will wait this number of seconds for the process to shutdown cleanly. At this amount of time, if the service is still running, the Bootstrap will `kill` the process, or terminate it abruptly. By default, this is set to `20`.
`java.arg.N` | Any number of JVM arguments can be passed to the NiFi Registry JVM when the process is started. These arguments are defined by adding properties to bootstrap.conf that begin with `java.arg.`. The rest of the property name is not relevant, other than to different property names, and will be ignored. The default includes properties for minimum and maximum Java Heap size, the garbage collector to use, etc.
`nifi.registry.bootstrap.sensitive.key` | The root key (in hexadecimal format) for encrypted sensitive configuration values. When NiFi Registry is started, this root key is used to decrypt sensitive values from the nifi-registry.properties file into memory for later use. The Encrypt-Config Tool can be used to specify the root key, encrypt sensitive values in nifi-registry.properties and update bootstrap.conf.

## Proxy Configuration

​When running Apache NiFi Registry behind a proxy there are a couple of key items to be aware of during deployment.

- NiFi Registry is comprised of a number of web applications (web UI, web API, documentation), so the mapping needs to be configured for the root path. That way all context paths are passed through accordingly.

- If NiFi Registry is running securely, any proxy needs to be authorized to proxy user requests. These can be configured in the NiFi Registry UI through the Users administration section, by selecting 'Proxy' for the given user. Once these permissions are in place, proxies can begin proxying user requests. The end user identity must be relayed in a HTTP header. For example, if the end user sent a request to the proxy, the proxy must authenticate the user. Following this the proxy can send the request to NiFi Registry. In this request an HTTP header should be added as follows.

    X-ProxiedEntitiesChain: <end-user-identity>

If the proxy is configured to send to another proxy, the request to NiFi Registry from the second proxy should contain a header as follows.

    X-ProxiedEntitiesChain: <end-user-identity><proxy-1-identity>

An example Apache proxy configuration that sets the required properties may look like the following. Complete proxy configuration is outside of the scope of this document. Please refer to the documentation of the proxy for guidance with your deployment environment and use case.

    ...
    <Location "/my-nifi">
        ...
    	SSLEngine On
    	SSLCertificateFile /path/to/proxy/certificate.crt
    	SSLCertificateKeyFile /path/to/proxy/key.key
    	SSLCACertificateFile /path/to/ca/certificate.crt
    	SSLVerifyClient require
    	RequestHeader add X-ProxyScheme "https"
    	RequestHeader add X-ProxyHost "proxy-host"
    	RequestHeader add X-ProxyPort "443"
    	RequestHeader add X-ProxyContextPath "/my-nifi-registry"
    	RequestHeader add X-ProxiedEntitiesChain "<%{SSL_CLIENT_S_DN}>"
    	ProxyPass https://nifi-registry-host:8443
    	ProxyPassReverse https://nifi-registry-host:8443
    	...
    </Location>
    ...

## Kerberos Service

NiFi Registry can be configured to use Kerberos SPNEGO (or "Kerberos Service") for authentication. In this scenario, users will hit the REST endpoint `/access/token/kerberos` and the server will respond with a `401` status code and the challenge response header `WWW-Authenticate: Negotiate`. This communicates to the browser to use the GSS-API and load the user’s Kerberos ticket and provide it as a Base64-encoded header value in the subsequent request. It will be of the form `Authorization: Negotiate YII…​`. NiFi Registry will attempt to validate this ticket with the KDC. If it is successful, the user’s principal will be returned as the identity, and the flow will follow login/credential authentication, in that a JWT will be issued in the response to prevent the unnecessary overhead of Kerberos authentication on every subsequent request. If the ticket cannot be validated, it will return with the appropriate error response code. The user will then be able to provide their Kerberos credentials to the login form if the `KerberosIdentityProvider` has been configured. See Kerberos Identity Provider for more details.

NiFi Registry will only respond to Kerberos SPNEGO negotiation over an HTTPS connection, as unsecured requests are never authenticated.

See Kerberos Properties for complete documentation.

### Notes

- Kerberos is case-sensitive in many places and the error messages (or lack thereof) may not be sufficiently explanatory. Check the case sensitivity of the service principal in your configuration files. The convention is `HTTP/fully.qualified.domain@REALM`.

- Browsers have varying levels of restriction when dealing with SPNEGO negotiations. Some will provide the local Kerberos ticket to any domain that requests it, while others whitelist the trusted domains. See Spring Security Kerberos - Reference Documentation: Appendix E. Configure browsers for SPNEGO Negotiation for common browsers.

- Some browsers (legacy IE) do not support recent encryption algorithms such as AES, and are restricted to legacy algorithms (DES). This should be noted when generating keytabs.

- The KDC must be configured and a service principal defined for NiFi and a keytab exported. Comprehensive instructions for Kerberos server configuration and administration are beyond the scope of this document (see MIT Kerberos Admin Guide), but an example is below.

Adding a service principal for a server at `nifi.nifi.apache.org` and exporting the keytab from the KDC:

    root@kdc:/etc/krb5kdc# kadmin.local
    Authenticating as principal admin/admin@NIFI.APACHE.ORG with password.
    kadmin.local:  listprincs
    K/M@NIFI.APACHE.ORG
    admin/admin@NIFI.APACHE.ORG
    ...
    kadmin.local:  addprinc -randkey HTTP/nifi.nifi.apache.org
    WARNING: no policy specified for HTTP/nifi.nifi.apache.org@NIFI.APACHE.ORG; defaulting to no policy
    Principal "HTTP/nifi.nifi.apache.org@NIFI.APACHE.ORG" created.
    kadmin.local:  ktadd -k /http-nifi.keytab HTTP/nifi.nifi.apache.org
    Entry for principal HTTP/nifi.nifi.apache.org with kvno 2, encryption type des3-cbc-sha1 added to keytab WRFILE:/http-nifi.keytab.
    Entry for principal HTTP/nifi.nifi.apache.org with kvno 2, encryption type des-cbc-crc added to keytab WRFILE:/http-nifi.keytab.
    kadmin.local:  listprincs
    HTTP/nifi.nifi.apache.org@NIFI.APACHE.ORG
    K/M@NIFI.APACHE.ORG
    admin/admin@NIFI.APACHE.ORG
    ...
    kadmin.local: q
    root@kdc:~# ll /http*
    -rw------- 1 root root 162 Mar 14 21:43 /http-nifi.keytab
    root@kdc:~#

## System Properties

The nifi-registry.properties file in the `conf` directory is the main configuration file for controlling how NiFi Registry runs. This section provides an overview of the properties in this file and includes some notes on how to configure it in a way that will make upgrading easier. After making changes to this file, restart NiFi Registry in order for the changes to take effect.

| Values for periods of time and data sizes must include the unit of measure, for example "10 secs" or "10 MB", not simply "10".

### Web Properties

These properties pertain to the web-based User Interface.

Property | Description
`nifi.registry.web.war.directory` | This is the location of the web war directory. The default value is `./lib`.
`nifi.registry.web.http.host` | The HTTP host. It is blank by default.
`nifi.registry.web.http.port` | The HTTP port. The default value is `18080`.
`nifi.registry.web.https.host` | The HTTPS host. It is blank by default.
`nifi.registry.web.https.port` | The HTTPS port. It is blank by default. When configuring NiFi Registry to run securely, this port should be configured.
`nifi.registry.web.https.application.protocols` | The space-separated list of application protocols supported when running with HTTPS enabled. The default value is `http/1.1`. The value can be set to `h2 http/1.1` to support Application Layer Protocol Negotiation (ALPN) for HTTP/2 or HTTP/1.1 based on client capabilities. The value can be set to `h2` to require HTTP/2 and disable HTTP/1.1.
`nifi.registry.web.jetty.working.directory` | The location of the Jetty working directory. The default value is `./work/jetty`.
`nifi.registry.web.jetty.threads` | The number of Jetty threads. The default value is `200`.

### Security Properties

These properties pertain to various security features in NiFi Registry. Many of these properties are covered in more detail in the Security Configuration section.

Property | Description
`nifi.registry.security.keystore` | The full path and name of the keystore. It is blank by default.
`nifi.registry.security.keystoreType` | The keystore type. It is blank by default.
`nifi.registry.security.keystorePasswd` | The keystore password. It is blank by default.
`nifi.registry.security.keyPasswd` | The key password. It is blank by default.
`nifi.registry.security.truststore` | The full path and name of the truststore. It is blank by default.
`nifi.registry.security.truststoreType` | The truststore type. It is blank by default.
`nifi.registry.security.truststorePasswd` | The truststore password. It is blank by default.
`nifi.registry.security.needClientAuth` | This specifies that connecting clients must authenticate with a client cert. Setting this to `false` will specify that connecting clients may optionally authenticate with a client cert, but may also login with a username and password against a configured identity provider. The default value is `true`.
`nifi.registry.security.authorizers.configuration.file` | This is the location of the file that specifies how authorizers are defined. The default value is `./conf/authorizers.xml`.
`nifi.registry.security.authorizer` | Specifies which of the configured Authorizers in the authorizers.xml file to use. By default, it is set to `managed-authorizer`.
`nifi.registry.security.identity.providers.configuration.file` | This is the location of the file that specifies how username/password authentication is performed. This file is only considered if `nifi.registry.security.identity.provider` is configured with a provider identifier. The default value is `./conf/identity-providers.xml`.
`nifi.registry.security.identity.provider` | This indicates what type of identity provider to use. The default value is blank, can be set to the identifier from a provider in the file specified in `nifi.registry.security.identity.providers.configuration.file`. Setting this property will trigger NiFi Registry to support username/password authentication.

### Identity Mapping Properties

These properties can be utilized to normalize user identities. When implemented, identities authenticated by different identity providers (certificates, LDAP, Kerberos) are treated the same internally in NiFi Registry. As a result, duplicate users are avoided and user-specific configurations such as authorizations only need to be setup once per user.

The following examples demonstrate normalizing DNs from certificates and principals from Kerberos:

    nifi.registry.security.identity.mapping.pattern.dn=^CN=(.*?), OU=(.*?), O=(.*?), L=(.*?), ST=(.*?), C=(.*?)$
    nifi.registry.security.identity.mapping.value.dn=$1@$2
    nifi.registry.security.identity.mapping.transform.dn=NONE
    nifi.registry.security.identity.mapping.pattern.kerb=^(.*?)/instance@(.*?)$
    nifi.registry.security.identity.mapping.value.kerb=$1@$2
    nifi.registry.security.identity.mapping.transform.kerb=NONE

The last segment of each property is an identifier used to associate the pattern with the replacement value. When a user makes a request to NiFi Registry, their identity is checked to see if it matches each of those patterns in lexicographical order. For the first one that matches, the replacement specified in the `nifi.registry.security.identity.mapping.value.xxxx` property is used. So a login with `CN=localhost, OU=Apache NiFi, O=Apache, L=Santa Monica, ST=CA, C=US` matches the DN mapping pattern above and the DN mapping value `$1@$2` is applied. The user is normalized to `localhost@Apache NiFi`.

In addition to mapping, a transform may be applied. The supported versions are `NONE` (no transform applied), `LOWER` (identity lowercased), and `UPPER` (identity uppercased). If not specified, the default value is `NONE`.

| These mappings are also applied to the "Initial Admin Identity" in the authorizers.xml file, as well as users imported from LDAP (See Authorizers.xml Setup).

Group names can also be mapped. The following example will accept the existing group name but will lowercase it. This may be helpful when used in conjunction with an external authorizer.

    nifi.registry.security.group.mapping.pattern.anygroup=^(.*)$
    nifi.registry.security.group.mapping.value.anygroup=$1
    nifi.registry.security.group.mapping.transform.anygroup=LOWER

| These mappings are applied to groups imported from LDAP.

### Providers Properties

These properties pertain to flow persistence providers. NiFi Registry uses a pluggable flow persistence provider to store the content of the flows saved to the registry. For further details on persistence providers, refer Persistence Providers.

Property | Description
`nifi.registry.providers.configuration.file` | This is the location of the file where flow persistence providers are configured. The default value is `./conf/providers.xml`.

### Alias Properties

These properties pertain to the support for URL aliasing. For further details, refer to URL Aliasing.

Property | Description
`nifi.registry.registry.alias.configuration.file` | This is the location of the file where URL aliases are configured. The default value is `./conf/registry-aliases.xml`.

### Database Properties

These properties define the settings for the Registry database, which keeps track of metadata about buckets and all items stored in buckets.

The 0.1.0 release leveraged an embedded H2 database that was configured via the following properties:

Property | Description
`nifi.registry.db.directory` | The location of the Registry database directory. The default value is `./database`.
`nifi.registry.db.url.append` | This property specifies additional arguments to add to the connection string for the Registry database. The default value should be used and should not be changed. It is: `;LOCK_TIMEOUT=25000;WRITE_DELAY=0;AUTO_SERVER=FALSE`.

The 0.2.0 release introduced a more flexible approach which allows leveraging an external database. This new approach is configured via the following properties:

Property | Description
`nifi.registry.db.url` | The full JDBC connection string. The default value will specify a new H2 database in the same location as the previous one. For example, `jdbc:h2:./database/nifi-registry-primary;`.
`nifi.registry.db.driver.class` | The class name of the JDBC driver. The default value is `org.h2.Driver`.
`nifi.registry.db.driver.directory` | An optional directory containing one or more JARs to add to the classpath. If not specified, it is assumed that the driver JAR is already on the classpath by copying it to the `lib` directory. The H2 driver is bundled with Registry so it is not necessary to do anything for the default case.
`nifi.registry.db.username` | The username for the database. The default value is `nifireg`.
`nifi.registry.db.password` | The password for the database. The default value is `nifireg`.
`nifi.registry.db.maxConnections` | The max number of connections for the connection pool. The default value is `5`.
`nifi.registry.db.sql.debug` | Whether or not enable debug logging for SQL statements. The default value is `false`.

| When upgrading from 0.1.0 to a future version, if `nifi.registry.db.directory` remains populated, the application will attempt to migrate the data from the original database to the new database specified with the new properties. This will only happen the first time the application starts with the new database properties.

### Extension Directories

Each property beginning with `nifi.registry.extension.dir.` will be treated as location for an extension, and a class loader will be created for each location, with the system class loader as the parent.

Property | Description
`nifi.registry.extension.dir.1` | The full path on the filesystem to the location of the JARs for the given extension

| Multiple extension directories can be specified by using the `nifi.registry.extension.dir.` prefix with unique suffixes and separate paths as values. For example, to provide an additional extension directory, a user could also specify additional properties with keys of: `nifi.registry.extension.dir.2=/path/to/extension2`, providing 2 total locations, including `nifi.registry.extension.dir.1`.

### Kerberos Properties

Property | Description
`nifi.registry.kerberos.krb5.file` | The location of the krb5 file, if used. It is blank by default. At this time, only a single krb5 file is allowed to be specified per NiFi instance, so this property is configured here to support SPNEGO and service principals rather than in individual Processors. If necessary the krb5 file can support multiple realms. Example: `/etc/krb5.conf`
`nifi.registry.kerberos.spnego.principal` | The name of the NiFi Registry Kerberos SPNEGO principal, if used. It is blank by default. Note that this property is used to authenticate NiFi Registry users. Example: `HTTP/nifi.registry.example.com` or `HTTP/nifi.registry.example.com@EXAMPLE.COM`
`nifi.registry.kerberos.spnego.keytab.location` | The file path of the NiFi Registry Kerberos SPNEGO keytab, if used. It is blank by default. Note that this property is used to authenticate NiFi Registry users. Example: `/etc/http-nifi-registry.keytab`
`nifi.registry.kerberos.spengo.authentication.expiration` | The expiration duration of a successful Kerberos user authentication, if used. The default value is `12 hours`.

## Metadata Database

The metadata database maintains the knowledge of which buckets exist, which versioned items belong to which buckets, as well as the version history for each item.

Currently, NiFi Registry supports using H2, Postgres (10.x - 13.x), and MySQL (8.0) for the relational database engine.

| NiFi Registry 0.1.0 only supports H2.

### H2

H2 is an embedded database that is pre-configured in the default nifi-registry.properties file. The contents of the H2 database are stored in a file on the local filesystem.

For NiFi Registry 0.1.0, the location of the H2 database is specified by the property:

`nifi.registry.db.directory=./database`

For NiFi Registry 0.2.0 and forward, the location of the H2 database is specified as part of the JDBC URL property:

`nifi.registry.db.url=jdbc:h2:./database/nifi-registry-primary;`

#### Changing password in existing H2 database

1. Download H2 driver from official repository https://www.h2database.com/html/download.html and place it somewhere accessible to NiFi Registry user

2. Run H2 database shell

       java -cp h2*.jar org.h2.tools.Shell

3. Connect to database

       Welcome to H2 Shell 2.1
       Exit with Ctrl+C
       URL       jdbc:h2:./database/nifi-registry-primary
       Driver    org.h2.Driver
       User      nifireg
       Password
       Connected

4. Change password

       ALTER USER nifireg SET PASSWORD 'NEW_PASSWORD';

### Postgres

Postgres provides the option to use an externally located database that also supports high availability.

The following steps are required to use Postgres:

1. Download the Postgres JDBC driver and place it somewhere accessible to NiFi Registry

       /path/to/drivers/postgresql-42.2.2.jar

2. Create a database inside Postgres

       createdb nifireg

3. Create a database user and grant privileges

       psql nifireg
       CREATE USER nifireg WITH PASSWORD 'changeme';
       GRANT ALL PRIVILEGES ON DATABASE nifireg to nifireg;
       \q

4. Configure the database properties in nifi-registry.properties

       nifi.registry.db.url=jdbc:postgresql://<POSTGRES-HOSTNAME>/nifireg
       nifi.registry.db.driver.class=org.postgresql.Driver
       nifi.registry.db.driver.directory=/path/to/drivers
       nifi.registry.db.username=nifireg
       nifi.registry.db.password=changeme

### MySQL

MySQL also provides the option to use an externally located database that also supports high availability.

The following steps are required to use MySQL:

1. Download the MySQL JDBC driver and place it somewhere accessible to NiFi Registry

       /path/to/drivers/mysql-connector-java-8.0.16.jar

2. Create a database inside MySQL (enter mysql shell using `mysql -u root -p`

       CREATE DATABASE nifi_registry;

3. Create a database user and grant privileges (for remote users, use `nifireg'@'<IP-ADDRESS>`, or `nifireg'@'%` for any remote host)

       GRANT ALL PRIVILEGES ON nifi_registry.* TO 'nifireg'@'localhost' IDENTIFIED BY 'changeme';

4. Configure the database properties in nifi-registry.properties

       nifi.registry.db.url=jdbc:mysql://<MYSQL-HOSTNAME>/nifi_registry
       nifi.registry.db.driver.class=com.mysql.cj.jdbc.Driver
       nifi.registry.db.driver.directory=/path/to/drivers
       nifi.registry.db.username=nifireg
       nifi.registry.db.password=changeme

## Schema Differences & Limitations

Due to differences across database implementations, there are two versions of the schema for NiFi Registry’s metadata database. The original version supports H2 and Postgres, and a second versions supports MySQL.

MySQL has limitations on the maximum size of text columns that are part of an index, or unique key. This means the maximum length of some columns is significantly less when using MySQL vs. H2/Postgres.

| If choosing to use MySQL it is important to understand these limitations and accept them.

The following tables summarizes the schema differences in column lengths:

Table.Column | H2/Postgres | MySQL
BUCKET.NAME | 1000 | 767
FLOW_SNAPSHOT.CREATED_BY | 4096 | 767
SIGNING_KEY.TENANT_IDENTITY | 4096 | 767
BUNDLE.GROUP_ID | 500 | 200
BUNDLE.ARTIFACT_ID | 500 | 200
BUNDLE_VERSION.CREATED_BY | 4096 | 767
BUNDLE_VERSION.BUILT_BY | 4096 | 767
BUNDLE_VERSION_DEPENDENCY.GROUP_ID | 500 | 200
BUNDLE_VERSION_DEPENDENCY.ARTIFACT_ID | 500 | 200
EXTENSION_PROVIDED_SERVICE_API.CLASS_NAME | 500 | 200
EXTENSION_PROVIDED_SERVICE_API.GROUP_ID | 500 | 200
EXTENSION_PROVIDED_SERVICE_API.ARTIFACT_ID | 500 | 200

## Persistence Providers

NiFi Registry uses a pluggable persistence provider to store the content of each versioned item. Each type of versioned item, such as a versioned flow or extension bundle, has its own persistence provider.

Each persistence provider has its own configuration parameters, which can be configured in an XML file specified in nifi-registry.properties.

### Flow Persistence Providers

The flow persistence provider stores the content of the flows saved to the registry. NiFi Registry provides `FileSystemFlowPersistenceProvider` and `GitFlowPersistenceProvider`.

The XML configuration file looks like below. It has a `flowPersistenceProvider` element in which qualified class name of a persistence provider implementation and its configuration properties are defined. See following sections for available configurations for each provider.

Example flow persistence provider in providers.xml

    <flowPersistenceProvider>
        <class>persistence-provider-qualified-class-name</class>
        <property name="property-1">property-value-1</property>
        <property name="property-2">property-value-2</property>
        <property name="property-n">property-value-n</property>
    </flowPersistenceProvider>

#### FileSystemFlowPersistenceProvider

FileSystemFlowPersistenceProvider simply stores serialized Flow contents into `{bucket-id}/{flow-id}/{version}` directories.

Example of persisted files:

    Flow Storage Directory/
    ├── {bucket-id}/
    │   └── {flow-id}/
    │       ├── {version}/{version}.snapshot
    └── d1beba88-32e9-45d1-bfe9-057cc41f7ce8/
        └── 219cf539-427f-43be-9294-0644fb07ca63/
            ├── 1/1.snapshot
            └── 2/2.snapshot

Qualified class name: `org.apache.nifi.registry.provider.flow.FileSystemFlowPersistenceProvider`

Property | Description
`Flow Storage Directory` | REQUIRED: File system path for a directory where flow contents files are persisted to. If the directory does not exist when NiFi Registry starts, it will be created. If the directory exists, it must be readable and writable from NiFi Registry.

#### GitFlowPersistenceProvider

`GitFlowPersistenceProvider` stores flow contents under a Git directory.

In contrast to `FileSystemFlowPersistenceProvider`, this provider uses human friendly Bucket and Flow names so that those files can be accessed by external tools. However, it is NOT supported to modify stored files outside of NiFi Registry. Persisted files are only read when NiFi Registry starts up.

Buckets are represented as directories and Flow contents are stored as files in a Bucket directory they belong to. Flow snapshot histories are managed as Git commits, meaning only the latest version of Buckets and Flows exist in the Git directory. Old versions are retrieved from Git commit histories.

Example persisted files

    Flow Storage Directory/
    ├── .git/
    ├── Bucket_A/
    │   ├── bucket.yml
    │   ├── Flow_1.snapshot
    │   └── Flow_2.snapshot
    └── Bucket_B/
        ├── bucket.yml
        └── Flow_4.snapshot

Each Bucket directory contains a YAML file named `bucket.yml`. The file manages links from NiFi Registry Bucket and Flow IDs to actual directory and file names. When NiFi Registry starts, this provider reads through Git commit histories and lookup these `bucket.yml` files to restore Buckets and Flows for each snapshot version.

Example bucket.yml

    layoutVer: 1
    bucketId: d1beba88-32e9-45d1-bfe9-057cc41f7ce8
    flows:
      219cf539-427f-43be-9294-0644fb07ca63: {ver: 7, file: Flow_1.snapshot}
      22cccb6c-3011-4493-a996-611f8f112969: {ver: 3, file: Flow_2.snapshot}

Qualified class name: `org.apache.nifi.registry.provider.flow.git.GitFlowPersistenceProvider`

Property | Description
`Flow Storage Directory` | REQUIRED: File system path for a directory where flow contents files are persisted to. The directory must exist when NiFi registry starts. Also must be initialized as a Git directory. See Initialize Git directory for detail.
`Remote To Push` | When a new flow snapshot is created, this persistence provider updates files in the specified Git directory, then creates a commit to the local repository. If `Remote To Push` is defined, it also pushes to the specified remote repository (e.g. `origin`). To define more detailed remote spec such as branch names, use `Refspec` (see https://git-scm.com/book/en/v2/Git-Internals-The-Refspec).
`Remote Access User` | This username is used to make push requests to the remote repository when `Remote To Push` is enabled, and the remote repository is accessed by HTTP protocol. If SSH is used, user authentication is done with SSH keys.
`Remote Access Password` | The password for the `Remote Access User`.
`Remote Clone Repository` | Remote repository URI to use to clone into `Flow Storage Directory`, if local repository is not present in `Flow Storage Directory`. If left empty the git directory needs to be configured as per Initialize Git directory. If URI is provided then `Remote Access User` and `Remote Access Password` also should be present. Currently, default branch of remote will be cloned.

##### Initialize Git directory

In order to use `GitFlowPersistenceRepository`, you need to prepare a Git directory on the local file system. You can do so by initializing a directory with `git init` command, or clone an existing Git project from a remote Git repository by `git clone` command. If you want to clone the default branch of remote repository automatically, set the `Remote Clone Repository` as described above.

- `git init` command https://git-scm.com/docs/git-init

- `git clone` command https://git-scm.com/docs/git-clone

##### Git user configuration

This persistence provider uses preconfigured Git user name and user email address when it creates Git commits. NiFi Registry user name is added to commit messages.

Example commit

    commit 774d4bd125f2b1200f0a5ee1f1e9fedc6a415e83
    Author: git-user <git-user@example.com>
    Date:   Tue May 8 14:30:31 2018 +0900

        Commit message.

        By NiFi Registry user: nifi-registry-user-1

You can configure Git user name and email address by `git config` command.

- `git config` command https://git-scm.com/docs/git-config

##### Git user authentication

By default, this persistence repository only create commits to local repository. No user authentication is needed to do so. However, if 'Commit To Push' is enabled, user authentication to the remote Git repository is required.

If the remote repository is accessed by HTTP, then username and password for authentication can be configured in the providers XML configuration file.

When SSH is used, SSH keys are used to identify a Git user. In order to pick the right key to a remote server, the SSH configuration file `${USER_HOME}/.ssh/config` is used. The SSH configuration file can contain multiple `Host` entries to specify a key file to login to a remote Git server. The `Host` must match with the target remote Git server hostname.

example SSH config file

    Host git.example.com
      HostName git.example.com
      IdentityFile ~/.ssh/id_rsa

    Host github.com
      HostName github.com
      IdentityFile ~/.ssh/key-for-github

    Host bitbucket.org
      HostName bitbucket.org
      IdentityFile ~/.ssh/key-for-bitbucket

#### DatabaseFlowPersistenceProvider

`DatabaseFlowPersistenceProvider` stores flow contents in a database table.

This provider leverages the same database used for the metadata database, so there is no configuration to provide since the connection details will come from the database properties in `nifi-registry.properties`.

The database table is named `FLOW_PERSISTENCE_PROVIDER` and has the following schema:

Column | Description
BUCKET_ID | The identifier of the bucket where the flow is located.
FLOW_ID | The identifier of the flow.
VERSION | The version of the flow.
FLOW_CONTENT | The serialized bytes of the flow content stored as a BLOB.

#### Switching from other Flow Persistence Provider

In order to switch the Flow Persistence Provider, it is necessary to reset NiFi Registry. For example, to switch from `FileSystemFlowPersistenceProvider` to `GitFlowPersistenceProvider`, follow these steps:

1. Stop version control on all ProcessGroups in NiFi

2. Stop NiFi Registry

3. Move the H2 DB (specified as `nifi.registry.db.directory` in nifi-registry.properties) and `Flow Storage Directory` for `FileSystemFlowPersistenceProvider` directories somewhere for back up

4. Configure `GitFlowPersistenceProvider` provider in providers.xml

5. Start NiFi Registry

6. Recreate any buckets

7. Start version control on all ProcessGroups again

#### Data model version of serialized Flow snapshots

Serialized Flow snapshots saved by these persistence providers have versions, so that the data format and schema can evolve over time. Data model version update is done automatically by NiFi Registry when it reads and stores each Flow content.

Here is the data model version histories:

Data model version | Since NiFi Registry | Description
2 | 0.2 | JSON formatted text file. The root object contains header and Flow content object.
1 | 0.1 | Binary format having header bytes at the beginning followed by Flow content represented as XML.

### Bundle Persistence Providers

The bundle persistence provider stores the content of extension bundles saved to the registry. NiFi Registry provides `FileSystemBundlePersistenceProvider` and `S3BundlePersistenceProvider`.

The XML configuration file looks like below. It has a `extensionBundlePersistenceProvider` element in which the qualified class name of a persistence provider implementation and its configuration properties are defined. See following sections for available configurations for each provider.

Example extension bundle persistence provider in providers.xml

    <extensionBundlePersistenceProvider>
        <class>persistence-provider-qualified-class-name</class>
        <property name="property-1">property-value-1</property>
        <property name="property-2">property-value-2</property>
        <property name="property-n">property-value-n</property>
    </extensionBundlePersistenceProvider>

#### FileSystemBundlePersistenceProvider

The `FileSystemBundlePersistenceProvider` stores the content of extension bundles on the local file system. The bundles are organized in directories according to bucket id, group, artifact, and version.

Example of persisted extension bundles:

    Extension Bundle Storage Directory/
    ├── {bucket-id}/
       └── {group-id}/
           └── {artifact-id}
               └── {version}/{artifact-id}-{version}.{extension}
    ├── d1beba88-32e9-45d1-bfe9-057cc41f7ce8/
        └── org.apache.nifi
            └── nifi-example-nar
                └── 1.0.0/nifi-example-nar-1.0.0.nar
                └── 2.0.0/nifi-example-nar-2.0.0.nar

##### Configuration

Qualified class name: `org.apache.nifi.registry.provider.extension.FileSystemBundlePersistenceProvider`

Property | Description
`Extension Bundle Storage Directory` | REQUIRED: File system path for a directory where extension bundle contents files are persisted to. If the directory does not exist when NiFi Registry starts, it will be created. If the directory exists, it must be readable and writable from NiFi Registry.

#### S3BundlePersistenceProvider

The `S3BundlePersistenceProvider` stores the content of extension bundles in a AWS S3 bucket. The bucket is expected to already exist and be accessible to the credentials provided to the persistence providcer.

| This provider must be added to the classpath by specifying a custom extension directory in nifi-registry.properties, such as `nifi.registry.extension.dir.aws=./ext/aws/lib`, where `./ext/aws/` contains the contents of the extracted nifi-registry-aws-assembly-<version>-bin.zip.

The key of an extension bundle in the S3 bucket will be the following:

    /{registry-bucket-id}/{group-id}/{artifact-id}/{version}/{artifact-id}-{version}.{extension}

If an optional Key Prefix is specified, then that prefix will be applied to the beginning of the above key.

##### Configuration

Qualified class name: `org.apache.nifi.registry.aws.S3BundlePersistenceProvider`

Property | Description
`Region` | REQUIRED: The name of the S3 region where the bucket exists.
`Bucket Name` | REQUIRED: The name of an existing bucket to store extension bundles.
`Key Prefix` | An optional prefix that if specified will be added to the beginning of all S3 keys.
`Credentials Provider` | REQUIRED: Indicates how credentials will be provided, must be a value of `DEFAULT_CHAIN` or `STATIC`. `DEFAULT_CHAIN` will consider in order: Java system properties, environment variables, credential profiles (`~/.aws/credentials`). `STATIC` requires that `Access Key` and `Secret Access Key` be specified directly in this file.
`Access Key` | The access key to use when using `STATIC` credentials provider.
`Secret Access Key` | The secret access key to use when using `STATIC` credentials provider.
`Endpoint URL` | An optional URL that overrides the default AWS S3 endpoint URL. Set this when using an AWS S3 API compatible service hosted at a different URL.

## Event Hooks

Event hooks are an integration point that allows for custom code to to be triggered when NiFi Registry application events occur.

Event Name | Description
--- | ---
`CREATE_BUCKET` | A new registry bucket is created.
`CREATE_FLOW` | A new flow is created in a specified bucket. Only triggered on first time creation of a flow with a given name.
`CREATE_FLOW_VERSION` | A new version for a flow has been saved in the registry.
`UPDATE_BUCKET` | A bucket has been updated.
`UPDATE_FLOW` | A flow that exist in a bucket has been updated.
`DELETE_BUCKET` | An existing bucket in the registry is deleted.
`DELETE_FLOW` | An existing flow in the registry is deleted.
`REGISTRY_START` | Invoked once the NiFi Registry application has been successfully started. This is only invoked after a complete and successful start.

### Shared Event Hook Properties

There are certain properties that are shared amongst all of the NiFi Registry provided Event Hook implementations. Those properties and their purpose are listed below.

Property Name | Description
--- | ---
`Whitelisted Event Type` | Event types the hook provider configured with this property should respond to. If this property is left blank or not provided, all events will fire for the configured hook provider. Multiple `Whitelisted Event Type` can be specified and often are. For example, `<property name="Whitelisted Event Type 1">CREATE_FLOW</property>` and `<property name="Whitelisted Event Type 2">UPDATE_FLOW</property>` would invoke the configured hook provider for the `CREATE_FLOW` and `UPDATE_FLOW` event types.

### ScriptEventHookProvider

The `ScriptEventHookProvider` invokes a shell script that has been written by a user and placed on a file system that is accessible by the NiFi Registry instance that the provider is configured for.

    <eventHookProvider>
        <class>org.apache.nifi.registry.provider.hook.ScriptEventHookProvider</class>
        <property name="Script Path"></property>
        <property name="Working Directory"></property>
        <!-- optional -->
        <property name="Whitelisted Event Type 1">CREATE_FLOW</property>
        <property name="Whitelisted Event Type 2">UPDATE_FLOW</property>
    </eventHookProvider>

Property Name | Description
--- | ---
`Script Path` | Full path to a script that will executed for each event. The arguments to the script will be the event fields in the order they are specified for the given event type.
`Working Directory` | Working directory from where the commands will be executed.

### LoggingEventHookProvider

The `LoggingEventHookProvider` logs a string representation of each event using an SLF4J logger. The logger can be configured via NiFi Registry’s logback.xml, which by default contains an appender that writes to a log file named nifi-registry-event.log in the `logs` directory.

    <eventHookProvider>
        <class>org.apache.nifi.registry.provider.hook.LoggingEventHookProvider</class>
    </eventHookProvider>

## URL Aliasing

A versioned item may contain the URL of a registry instance embedded in the content of the item. For example, flows with nested versioning contain the URL of the registry where the nested versioned flow is located. If the location of the registry instances changes, then the content is no longer accurate.

URL aliasing can be used to dynamically handle this situation so that URLs are never written to the stored content, and can be re-written with the correct value when being retrieved by a client.

The aliases are configured in an XML file which can be specified in nifi-registry.properties.

Example aliases in registry-aliases.xml

    <aliases>
        <alias>
            <internal>NIFI_REGISTRY_1</internal>
            <external>http://registry1.nifi.apache.org:18080</external>
        </alias>
        <alias>
            <internal>NIFI_REGISTRY_2</internal>
            <external>http://registry2.nifi.apache.org:18080</external>
        </alias>
    </aliases>

If a flow is saved to registry with two child process groups, each under version control, the incoming flow would contain something like the following:

    "processGroups" : [ {
          ...
          "versionedFlowCoordinates" : {
            "bucketId" : "ca20e058-f6e7-404c-aee0-e30833e792c7",
            "flowId" : "178a6657-e1a7-4cce-8f83-4e615e38f57a",
            "registryUrl" : "http://registry1.nifi.apache.org:18080",
            "version" : 1
          },
          {
          ...
          "versionedFlowCoordinates" : {
            "bucketId" : "ca20e058-f6e7-404c-aee0-e30833e792c7",
            "flowId" : "985cb44b-3aec-32be-860f-d2a0f2c72aac",
            "registryUrl" : "http://registry2.nifi.apache.org:18080",
            "version" : 1
          }
    ]

With the example aliases configuration above, the URLs would be written to the flow persistence provider as the following:

    "processGroups" : [ {
          ...
          "versionedFlowCoordinates" : {
            "bucketId" : "ca20e058-f6e7-404c-aee0-e30833e792c7",
            "flowId" : "178a6657-e1a7-4cce-8f83-4e615e38f57a",
            "registryUrl" : "NIFI_REGISTRY_1",
            "version" : 1
          },
          {
          ...
          "versionedFlowCoordinates" : {
            "bucketId" : "ca20e058-f6e7-404c-aee0-e30833e792c7",
            "flowId" : "985cb44b-3aec-32be-860f-d2a0f2c72aac",
            "registryUrl" : "NIFI_REGISTRY_2",
            "version" : 1
          }
    ]

When this flow is retrieved from any API call, the internal values would be rewritten to the external values.

## Backup & Recovery

In order to prevent data loss it is important to consider backup and recovery options. The data that needs to be considered is the following:

- Metadata Database

- Persistence providers

- Configuration files

### Metadata Database

If using H2, the database file should be backed up periodically to an external location. In order to ensure a proper backup, NiFi Registry should be stopped to ensure no write operations are occurring while copying the file.

If using Postgres, backups may be taken on the Postgres database, or Postgres may be configured for high availability such that there is a failover or backup instance.

If starting a brand new NiFi Registry instance, the metadata database can be automatically rebuilt from the information in the `GitFlowPersistenceProvider`. This is a one-time operation during the first start of the application, and is not meant to keep the DB in sync with external changes made in Git. This feature only applies to flows and would not be able to restore information about extension bundles.

### Persistence Providers

Each persistence provider may have its own option for backup & recovery.

#### Flow Persistence

If using the `FileSystemFlowPersistenceProvider`, the directory where flows are stored should be backed up periodically to an external location. In order to ensure a proper backup, NiFi Registry should be stopped to ensure no flows are being written to disk. If using H2 for metadata, H2 should be backed up at the same time to ensure consistency between the flows on disk and the contents in H2.

If using the `GitFlowPersistenceProvider`, the ability to automatically push to a remote may be configured. This provides an automatic backup of the data in the remote repo.

### Bundle Persistence

If using the `FileSystemBundlePersistenceProvider`, the directory where bundles are stored should be backed up periodically to an external location. In order to ensure a proper backup, NiFi Registry should be stopped to ensure no bundles are being written to disk. If using H2 for metadata, H2 should be backed up at the same time to ensure consistency between the bundles on disk and the contents in H2.

If using the `S3BundlePersistenceProvider`, data will be stored remotely and automatically replicated.

### Configuration Files

If using NiFi Registry’s policy based authorization, the users, groups, and policies are stored in files on disk named users.xml and authorizations.xml. These files should be periodically backed up to an external location. In order to ensure a proper backup, NiFi Registry should be stopped to ensure no authorization data is being written to disk.