src/main/resources/Documentation/config.md - plugins/high-availability - Git at Google



            @PLUGIN@ Configuration

            
            =========================


            The @PLUGIN@ plugin must be installed on all the instances. Each instance should

            
            be configured with the same [gerrit.serverId](https://gerrit-documentation.storage.googleapis.com/Documentation/3.2.0/config-gerrit.html#gerrit.serverId).

            
            If there are existing changes in [NoteDb](https://gerrit-documentation.storage.googleapis.com/Documentation/3.2.0/note-db.html)

            
            made with another `serverId`, then this plugin might not be able to access them.

            
            Likewise, if the HA gerrit.serverIds differ, then changes conveyed by one

            
            instance will not be accessible by the other.


            The following fields should be specified in `$site_path/etc/@PLUGIN@.config` files:


            File '@PLUGIN@.config'

            
            --------------------


            ### Static definition of the high-availability nodes.


            ```

            
            [main]

            
              sharedDirectory = /directory/accessible/from/both/instances

            
            [peerInfo]

            
              strategy = static

            
            [peerInfo "static"]

            
              url = first_target_instance_url

            
              url = second_target_instance_url

            
            [http]

            
              user = username

            
              password = password

            
            ```


            ### Dynamic jgroups-based discovery of the high-availability nodes


            ```

            
            [main]

            
              sharedDirectory = /directory/accessible/from/both/instances

            
            [peerInfo]

            
              strategy = jgroups

            
            [peerInfo "jgroups"]

            
              myUrl = local_instance_url

            
            [jgroups]

            
              clusterName = foo

            
              skipInterface = lo*

            
              skipInterface = eth2

            
              protocolStack = protocolStack.xml

            
            [http]

            
              user = username

            
              password = password

            
            [healthcheck]

            
              enable = true

            
            ```


            ### JGroups based discovery and message transport


            In this case URLs of peers are not needed. All peers just need to join the same JGroups cluster

            
            defined by the `jgroups.clusterName`.

            
            ```

            
            [main]

            
              transport = jgroups

            
              sharedDirectory = /directory/accessible/from/both/instances

            
            [jgroups]

            
              clusterName = foo

            
              skipInterface = lo*

            
              skipInterface = eth2

            
              protocolStack = protocolStack.xml

            
              timeout = 5000

            
              maxTries = 100

            
            ```


            ### Transport implementation provided by another plugin


            In this case another plugin extends the @PLUGIN@ plugin and provides messaging

            
            implementation.

            
            ```

            
            [main]

            
              transport = provided

            
              sharedDirectory = /directory/accessible/from/both/instances

            
            ```


            ```main.sharedDirectory```

            
            :   Path to a directory accessible from both instances.

            
                When given as a relative path, then it is resolved against the $SITE_PATH

            
                or Gerrit server. For example, if $SITE_PATH is "/gerrit/root" and

            
                sharedDirectory is given as "shared/dir" then the real path of the shared

            
                directory is "/gerrit/root/shared/dir". When not specified, the default

            
                is "shared".


            ```main.transport```

            
            :   Message transport layer. Could be: `http`, `jgroups` or `provided`.

            
                When not specificed the default is `http`.

            
                When set to `jgroups` or `provided` then all `peerInfo.*` sections are

            
                unnecessary and ignored.


            **Note:** For projects and groups reindexing, [scheduled indexer](https://gerrit-review.googlesource.com/Documentation/config-gerrit.html#scheduledIndexer) can be enabled with specific configurations.

            
            Example configurations:


            ```

            
            [scheduledIndexer "groups"]

            
                enabled = true

            
                interval = 1h

            
                startTime = 13:00


            [scheduledIndexer "projects"]

            
                enabled = true

            
                interval = 1h

            
                startTime = 13:00

            
            ```

            
            Note: Ensure these settings are added to enable periodic reindexing of groups and projects.

            
            Groups and projects may become outdated if indexing events are missed due to the node being down or

            
            some networking issues.


            **NOTE:** The indexSync feature exposes a REST endpoint that can be used to discover project names.

            
            Admins are advised to restrict access to the REST endpoints exposed by this plugin.


            ```indexSync.enabled```

            
            :   When indexSync is enabled, the primary servers will synchronize indexes with the intention to

            
                self-heal any missed reindexing event.

            
                When not specified, the default is `false`.


            ```indexSync.delay```

            
            :   If enabled, index sync will start running after this initial delay.

            
                Delay is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                When not specified, the default is zero: run immediately.


            ```indexSync.period```

            
                Period between two index sync executions. If any execution of this task takes longer than

            
                this period, then subsequent executions may start late, but will not concurrently execute.

            
                Delay is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                When not specified, the default is `2 seconds`.


            ```indexSync.initialSyncAge```

            
                This options defines the max age of changes in the other peer for which local index shall

            
                be synchronized on the initial run of the index sync task. The age defined here is usualy

            
                larger than the `syncAge` in order to accommodate max foreseen downtime of a server during

            
                restarts.

            
                The age is express in the format of the `age:` change query parameter.

            
                When not specified, the default is `1hour`.


            ```indexSync.syncAge```

            
                This option defines the max age of changes in the other peer for this local index shall be

            
                synchronized on each run, except for the initial run.

            
                The age is express in the format of the `age:` change query parameter.

            
                When not specified, the default is `5minutes`.


            ```peerInfo.strategy```

            
            :   Strategy to find other peers. Supported strategies are `static` or `jgroups`.

            
                Defaults to `jgroups`.

            
            * The `static` strategy allows to staticly configure the peer gerrit instance using

            
            the configuration parameter `peerInfo.static.url`.

            
            * The `jgroups` strategy allows that a gerrit instance discovers the peer

            
            instance by using JGroups to send multicast messages. In this case the

            
            configuration parameters `peerInfo.jgroups.*` are used to control the sending of

            
            the multicast messages. During startup each instance will advertise its address

            
            over a JGroups multicast message. JGroups takes care to inform each cluster when

            
            a member joins or leaves the cluster.


            ```peerInfo.static.url```

            
            :   Specify the URL for the peer instance. If more than one peer instance is to be

            
                configured, add as many url entries as necessary.


            ```peerInfo.jgroups.myUrl```

            
            :   The URL of this instance to be broadcast to other peers. Alternatively, this URL

            
                can also be specified using the environment variable `GERRIT_URL`. This is useful

            
                in environments like Kubernetes, where manual configuration of each Gerrit

            
                instance is not possible.

            
                If neither the configuration option nor the system property is specified, the

            
                URL is determined from the `httpd.listenUrl` in the `gerrit.config`.

            
                If `httpd.listenUrl` is configured with multiple values, is configured to work

            
                with a reverse proxy (i.e. uses `proxy-http` or `proxy-https` scheme), or is

            
                configured to listen on all local addresses (i.e. using hostname `*`), then

            
                the URL must be explicitly specified with `myUrl`.


            ```jgroups.clusterName```

            
            :   The name of the high-availability cluster. When peers discover themselves dynamically this

            
                name is used to determine which instances should work together.  Only those Gerrit

            
                interfaces which are configured for the same clusterName will communicate with each other.

            
                Defaults to "GerritHA".


            ```jgroups.skipInterface```

            
            :   A name or a wildcard of network interface(s) which should be skipped

            
                for JGroups communication. Peer discovery may fail if the host has multiple

            
                network interfaces and an inappropriate interface is chosen by JGroups.

            
                This option can be repeated many times in the `jgroups` section.

            
                Defaults to the list of: `lo*`, `utun*`, `awdl*` which are known to be

            
                inappropriate for JGroups communication.


            ```jgroups.protocolStack```

            
            :   This optional parameter specifies the path of an xml file that contains the

            
                definition of JGroups protocol stack. If not specified the default protocol stack

            
                will be used. May be an absolute or relative path. If the path is relative it is

            
                resolved from the site's `etc` folder. For more information on protocol stack and

            
                its configuration file syntax please refer to JGroups documentation.

            
                See [JGroups - Advanced topics](http://jgroups.org/manual-3.x/html/user-advanced.html).


            ```jgroups.kubernetes```

            
            :   If true, a protocol stack optimized for Kubernetes will be used. Peers will be discovered

            
                by querying the Kubernetes API server for pods. The functionality is provided by the

            
                [jgroups-kubernetes extension](https://github.com/jgroups-extras/jgroups-kubernetes).

            
                To enable Gerrit to use the Kubernetes API, the pods require a ServiceAccount with

            
                permissions to list pods ([example](https://github.com/jgroups-extras/jgroups-kubernetes#demo)).

            
                Further, Gerrit requires a valid TLS certificate in its keystore, since the Kubernetes

            
                API server requires TLS. (Default: false)


            ```jgroups.kubernetes.namespace```

            
            :   The namespace in which to query for pods. (Default: default)


            ```jgroups.kubernetes.label```

            
            :   A label that will be used to select the pods in the format `label=value`. Can be set

            
                multiple times.


            ```jgroups.timeout```

            
            :   Maximum interval of time in milliseconds the JGroups wait for a response

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                forwarding a message. When not specified, the default value is 5 seconds.


            ```jgroups.maxTries```

            
            :   Maximum number of times JGroups should attempt to forward a messages. Must be at least 1.

            
                Setting this option to zero or negative will assume the default value.

            
                When not specified, the default value is 720 times.


            ```jgroups.retryInterval```

            
            :   The interval of time in milliseconds between the subsequent auto-retries.

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                When not specified, the default value is set to 10 seconds.


            ```jgroups.threadPoolSize```

            
            :   Maximum number of threads used to execute JGroups calls towards target instances.


            NOTE: the default settings for `jgroups.timeout` and `jgroups.maxTries` ensure

            
            that JGroups will keep retrying to forward a message for one hour.


            NOTE: To work properly in certain environments, JGroups needs the System property

            
            `java.net.preferIPv4Stack` to be set to `true`.

            
            See [JGroups - Trouble shooting](http://jgroups.org/tutorial/index.html#_trouble_shooting).


            ```http.user```

            
            :   Username to connect to the peer instance.


            ```http.password```

            
            :   Password to connect to the peer instance.


            @PLUGIN@ plugin uses REST API calls to keep the target instance in-sync. It

            
            is possible to customize the parameters of the underlying http client doing these

            
            calls by specifying the following fields:


            ```http.connectionTimeout```

            
            :   Maximum interval of time in milliseconds the plugin waits for a connection

            
                to the target instance.

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                When not specified, the default value is set to 5 seconds.


            ```http.socketTimeout```

            
            :   Maximum interval of time in milliseconds the plugin waits for a response from the

            
                target instance once the connection has been established.

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                When not specified, the default value is set to 5 seconds.


            ```http.maxTries```

            
            :   Maximum number of times the plugin should attempt when calling a REST API in

            
                the target instance. Must be at least 1.

            
                Setting this option to zero or negative will assume the default value;

            
                When not specified, the default value is 360. After this number of failed attempts, an

            
                error is logged.


            ```http.retryInterval```

            
            :   The interval of time in milliseconds between the subsequent auto-retries.

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                When not specified, the default value is set to 10 seconds.


            ```http.connectionsPerRoute```

            
            :   Maximum number of pooled HTTP connections to a peer instance.

            
                When not specified, the default value is 100.


            ```http.maxConnections```

            
            :   Total max pooled HTTP connections.

            
                When not specified, the default value is 200.


            ```http.threadPoolSize```

            
            :   Maximum number of threads used to execute REST calls towards target instances.


            ```cache.synchronize```

            
            :   Whether to synchronize cache evictions.

            
                Defaults to true.


            ```cache.pattern```

            
            :   Pattern to match names of custom caches for which evictions should be

            
                forwarded (in addition to the core caches that are always forwarded). May be

            
                specified more than once to add multiple patterns.

            
                Defaults to an empty list, meaning only evictions of the core caches are

            
                forwarded.


            ```event.allowedListeners```

            
            :   Class name or package name of the event listener that is always allowed to receive

            
                all events generated locally or from a remote end.

            
                Can be specified multiple times for allowing multiple listeners classes or packages.

            
                Defaults to an empty list.


            ```event.synchronize```

            
            :   Whether to synchronize stream events.

            
                Defaults to true.


            ```index.synchronize```

            
            :   Whether to synchronize secondary indexes.

            
                Defaults to true.


            ```index.synchronizeForced```

            
            :   Whether to synchronize forced index events. E.g. on-line reindex

            
                automatically triggered upon version upgrades.

            
                Defaults to true.


            ```index.threadPoolSize```

            
            :   Maximum number of threads used to process index events in the receiving gerrit instance.

            
                Defaults to 4.


            ```index.batchThreadPoolSize```

            
            :   Maximum number of threads used to process batch index events in the receiving gerrit instance

            
                and not associated to an interactive action performed by a user.

            
                Defaults to `index.threadPoolSize`.


            ```index.maxTries```

            
            :   Maximum number of times the plugin should attempt to reindex changes.

            
                Must be at least 1.

            
                Setting this option to zero or negative will assume the default value;

            
                After this number of failed tries, an error is logged and the local index should be considered

            
                stale and needs to be investigated and manually reindexed.

            
                Defaults to 2.


            ```index.initialDelay```

            
            :   The initial delay, internally converted in milliseconds, of triggering the

            
                indexing operation after the indexing even has been received.

            
                Typically needed when there is a well-known latency of propagation of the updates

            
                across the nodes sharing the same NFS volume.

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                Defaults to 0 milliseconds, meaning that indexing happens immediately when the indexing

            
                event is received.


            ```index.retryInterval```

            
            :   The interval of time in milliseconds between the subsequent auto-retries.

            
                Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).

            
                Defaults to 30 seconds.


            NOTE: the default settings for `http.socketTimeout` and `http.maxTries` ensure

            
            that the plugin will keep retrying to forward a message for one hour.


            ```websession.synchronize```

            
            :   Whether to synchronize web sessions.

            
                Defaults to true.


            ```websession.cleanupInterval```

            
            :   Frequency for deleting expired web sessions. Values should use common time

            
                unit suffixes to express their setting:

            
            * s, sec, second, seconds

            
            * m, min, minute, minutes

            
            * h, hr, hour, hours

            
            * d, day, days

            
            * w, week, weeks (`1 week` is treated as `7 days`)

            
            * mon, month, months (`1 month` is treated as `30 days`)

            
            * y, year, years (`1 year` is treated as `365 days`)

            
            If a time unit suffix is not specified, `hours` is assumed.

            
            Defaults to 24 hours.


            ```healthcheck.enable```

            
            :   Whether to enable the health check endpoint. Defaults to 'true'.


            ```ref-database.enabled```

            
            :   Enable the use of a global ref-database. Defaults to 'false'.


            ```ref-database.enforcementRules.<policy>```

            
            :   Level of consistency enforcement across sites on a project:refs basis.

            
                Supports two values for enforcing the policy on multiple projects or refs.

            
                If the project or ref is omitted, apply the policy to all projects or all refs.


                The <policy> can be one of the following values:


                1. REQUIRED - Throw an exception if a git ref-update is processed against

            
                a local ref not yet in sync with the global ref-database.

            
                The user transaction is cancelled. LOCK_FAILURE is reported upstream.


                2. IGNORED - Do not validate against the global ref-database.


                *Example:*

            
                ```

            
                [ref-database "enforcementRules"]

            
                   IGNORED = AProject:/refs/heads/feature

            
                ```


                Ignore the alignment with the global ref-db for AProject on refs/heads/feature.


                Defaults to no rule. All projects are REQUIRED to be consistent on all refs.

	@PLUGIN@ Configuration
	=========================

	The @PLUGIN@ plugin must be installed on all the instances. Each instance should
	be configured with the same [gerrit.serverId](https://gerrit-documentation.storage.googleapis.com/Documentation/3.2.0/config-gerrit.html#gerrit.serverId).
	If there are existing changes in [NoteDb](https://gerrit-documentation.storage.googleapis.com/Documentation/3.2.0/note-db.html)
	made with another `serverId`, then this plugin might not be able to access them.
	Likewise, if the HA gerrit.serverIds differ, then changes conveyed by one
	instance will not be accessible by the other.

	The following fields should be specified in `$site_path/etc/@PLUGIN@.config` files:

	File '@PLUGIN@.config'
	--------------------

	### Static definition of the high-availability nodes.

	```
	[main]
	sharedDirectory = /directory/accessible/from/both/instances
	[peerInfo]
	strategy = static
	[peerInfo "static"]
	url = first_target_instance_url
	url = second_target_instance_url
	[http]
	user = username
	password = password
	```

	### Dynamic jgroups-based discovery of the high-availability nodes

	```
	[main]
	sharedDirectory = /directory/accessible/from/both/instances
	[peerInfo]
	strategy = jgroups
	[peerInfo "jgroups"]
	myUrl = local_instance_url
	[jgroups]
	clusterName = foo
	skipInterface = lo*
	skipInterface = eth2
	protocolStack = protocolStack.xml
	[http]
	user = username
	password = password
	[healthcheck]
	enable = true
	```

	### JGroups based discovery and message transport

	In this case URLs of peers are not needed. All peers just need to join the same JGroups cluster
	defined by the `jgroups.clusterName`.
	```
	[main]
	transport = jgroups
	sharedDirectory = /directory/accessible/from/both/instances
	[jgroups]
	clusterName = foo
	skipInterface = lo*
	skipInterface = eth2
	protocolStack = protocolStack.xml
	timeout = 5000
	maxTries = 100
	```

	### Transport implementation provided by another plugin

	In this case another plugin extends the @PLUGIN@ plugin and provides messaging
	implementation.
	```
	[main]
	transport = provided
	sharedDirectory = /directory/accessible/from/both/instances
	```

	```main.sharedDirectory```
	: Path to a directory accessible from both instances.
	When given as a relative path, then it is resolved against the $SITE_PATH
	or Gerrit server. For example, if $SITE_PATH is "/gerrit/root" and
	sharedDirectory is given as "shared/dir" then the real path of the shared
	directory is "/gerrit/root/shared/dir". When not specified, the default
	is "shared".

	```main.transport```
	: Message transport layer. Could be: `http`, `jgroups` or `provided`.
	When not specificed the default is `http`.
	When set to `jgroups` or `provided` then all `peerInfo.*` sections are
	unnecessary and ignored.

	Note: For projects and groups reindexing, [scheduled indexer](https://gerrit-review.googlesource.com/Documentation/config-gerrit.html#scheduledIndexer) can be enabled with specific configurations.
	Example configurations:

	```
	[scheduledIndexer "groups"]
	enabled = true
	interval = 1h
	startTime = 13:00

	[scheduledIndexer "projects"]
	enabled = true
	interval = 1h
	startTime = 13:00
	```
	Note: Ensure these settings are added to enable periodic reindexing of groups and projects.
	Groups and projects may become outdated if indexing events are missed due to the node being down or
	some networking issues.

	NOTE: The indexSync feature exposes a REST endpoint that can be used to discover project names.
	Admins are advised to restrict access to the REST endpoints exposed by this plugin.

	```indexSync.enabled```
	: When indexSync is enabled, the primary servers will synchronize indexes with the intention to
	self-heal any missed reindexing event.
	When not specified, the default is `false`.

	```indexSync.delay```
	: If enabled, index sync will start running after this initial delay.
	Delay is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	When not specified, the default is zero: run immediately.

	```indexSync.period```
	Period between two index sync executions. If any execution of this task takes longer than
	this period, then subsequent executions may start late, but will not concurrently execute.
	Delay is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	When not specified, the default is `2 seconds`.

	```indexSync.initialSyncAge```
	This options defines the max age of changes in the other peer for which local index shall
	be synchronized on the initial run of the index sync task. The age defined here is usualy
	larger than the `syncAge` in order to accommodate max foreseen downtime of a server during
	restarts.
	The age is express in the format of the `age:` change query parameter.
	When not specified, the default is `1hour`.

	```indexSync.syncAge```
	This option defines the max age of changes in the other peer for this local index shall be
	synchronized on each run, except for the initial run.
	The age is express in the format of the `age:` change query parameter.
	When not specified, the default is `5minutes`.


	```peerInfo.strategy```
	: Strategy to find other peers. Supported strategies are `static` or `jgroups`.
	Defaults to `jgroups`.
	* The `static` strategy allows to staticly configure the peer gerrit instance using
	the configuration parameter `peerInfo.static.url`.
	* The `jgroups` strategy allows that a gerrit instance discovers the peer
	instance by using JGroups to send multicast messages. In this case the
	configuration parameters `peerInfo.jgroups.*` are used to control the sending of
	the multicast messages. During startup each instance will advertise its address
	over a JGroups multicast message. JGroups takes care to inform each cluster when
	a member joins or leaves the cluster.

	```peerInfo.static.url```
	: Specify the URL for the peer instance. If more than one peer instance is to be
	configured, add as many url entries as necessary.

	```peerInfo.jgroups.myUrl```
	: The URL of this instance to be broadcast to other peers. Alternatively, this URL
	can also be specified using the environment variable `GERRIT_URL`. This is useful
	in environments like Kubernetes, where manual configuration of each Gerrit
	instance is not possible.
	If neither the configuration option nor the system property is specified, the
	URL is determined from the `httpd.listenUrl` in the `gerrit.config`.
	If `httpd.listenUrl` is configured with multiple values, is configured to work
	with a reverse proxy (i.e. uses `proxy-http` or `proxy-https` scheme), or is
	configured to listen on all local addresses (i.e. using hostname `*`), then
	the URL must be explicitly specified with `myUrl`.

	```jgroups.clusterName```
	: The name of the high-availability cluster. When peers discover themselves dynamically this
	name is used to determine which instances should work together. Only those Gerrit
	interfaces which are configured for the same clusterName will communicate with each other.
	Defaults to "GerritHA".

	```jgroups.skipInterface```
	: A name or a wildcard of network interface(s) which should be skipped
	for JGroups communication. Peer discovery may fail if the host has multiple
	network interfaces and an inappropriate interface is chosen by JGroups.
	This option can be repeated many times in the `jgroups` section.
	Defaults to the list of: `lo`, `utun`, `awdl*` which are known to be
	inappropriate for JGroups communication.

	```jgroups.protocolStack```
	: This optional parameter specifies the path of an xml file that contains the
	definition of JGroups protocol stack. If not specified the default protocol stack
	will be used. May be an absolute or relative path. If the path is relative it is
	resolved from the site's `etc` folder. For more information on protocol stack and
	its configuration file syntax please refer to JGroups documentation.
	See [JGroups - Advanced topics](http://jgroups.org/manual-3.x/html/user-advanced.html).

	```jgroups.kubernetes```
	: If true, a protocol stack optimized for Kubernetes will be used. Peers will be discovered
	by querying the Kubernetes API server for pods. The functionality is provided by the
	[jgroups-kubernetes extension](https://github.com/jgroups-extras/jgroups-kubernetes).
	To enable Gerrit to use the Kubernetes API, the pods require a ServiceAccount with
	permissions to list pods ([example](https://github.com/jgroups-extras/jgroups-kubernetes#demo)).
	Further, Gerrit requires a valid TLS certificate in its keystore, since the Kubernetes
	API server requires TLS. (Default: false)

	```jgroups.kubernetes.namespace```
	: The namespace in which to query for pods. (Default: default)

	```jgroups.kubernetes.label```
	: A label that will be used to select the pods in the format `label=value`. Can be set
	multiple times.

	```jgroups.timeout```
	: Maximum interval of time in milliseconds the JGroups wait for a response
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	forwarding a message. When not specified, the default value is 5 seconds.

	```jgroups.maxTries```
	: Maximum number of times JGroups should attempt to forward a messages. Must be at least 1.
	Setting this option to zero or negative will assume the default value.
	When not specified, the default value is 720 times.

	```jgroups.retryInterval```
	: The interval of time in milliseconds between the subsequent auto-retries.
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	When not specified, the default value is set to 10 seconds.

	```jgroups.threadPoolSize```
	: Maximum number of threads used to execute JGroups calls towards target instances.

	NOTE: the default settings for `jgroups.timeout` and `jgroups.maxTries` ensure
	that JGroups will keep retrying to forward a message for one hour.

	NOTE: To work properly in certain environments, JGroups needs the System property
	`java.net.preferIPv4Stack` to be set to `true`.
	See [JGroups - Trouble shooting](http://jgroups.org/tutorial/index.html#_trouble_shooting).

	```http.user```
	: Username to connect to the peer instance.

	```http.password```
	: Password to connect to the peer instance.

	@PLUGIN@ plugin uses REST API calls to keep the target instance in-sync. It
	is possible to customize the parameters of the underlying http client doing these
	calls by specifying the following fields:

	```http.connectionTimeout```
	: Maximum interval of time in milliseconds the plugin waits for a connection
	to the target instance.
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	When not specified, the default value is set to 5 seconds.

	```http.socketTimeout```
	: Maximum interval of time in milliseconds the plugin waits for a response from the
	target instance once the connection has been established.
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	When not specified, the default value is set to 5 seconds.

	```http.maxTries```
	: Maximum number of times the plugin should attempt when calling a REST API in
	the target instance. Must be at least 1.
	Setting this option to zero or negative will assume the default value;
	When not specified, the default value is 360. After this number of failed attempts, an
	error is logged.

	```http.retryInterval```
	: The interval of time in milliseconds between the subsequent auto-retries.
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	When not specified, the default value is set to 10 seconds.

	```http.connectionsPerRoute```
	: Maximum number of pooled HTTP connections to a peer instance.
	When not specified, the default value is 100.

	```http.maxConnections```
	: Total max pooled HTTP connections.
	When not specified, the default value is 200.

	```http.threadPoolSize```
	: Maximum number of threads used to execute REST calls towards target instances.

	```cache.synchronize```
	: Whether to synchronize cache evictions.
	Defaults to true.

	```cache.pattern```
	: Pattern to match names of custom caches for which evictions should be
	forwarded (in addition to the core caches that are always forwarded). May be
	specified more than once to add multiple patterns.
	Defaults to an empty list, meaning only evictions of the core caches are
	forwarded.

	```event.allowedListeners```
	: Class name or package name of the event listener that is always allowed to receive
	all events generated locally or from a remote end.
	Can be specified multiple times for allowing multiple listeners classes or packages.
	Defaults to an empty list.

	```event.synchronize```
	: Whether to synchronize stream events.
	Defaults to true.

	```index.synchronize```
	: Whether to synchronize secondary indexes.
	Defaults to true.

	```index.synchronizeForced```
	: Whether to synchronize forced index events. E.g. on-line reindex
	automatically triggered upon version upgrades.
	Defaults to true.

	```index.threadPoolSize```
	: Maximum number of threads used to process index events in the receiving gerrit instance.
	Defaults to 4.

	```index.batchThreadPoolSize```
	: Maximum number of threads used to process batch index events in the receiving gerrit instance
	and not associated to an interactive action performed by a user.
	Defaults to `index.threadPoolSize`.

	```index.maxTries```
	: Maximum number of times the plugin should attempt to reindex changes.
	Must be at least 1.
	Setting this option to zero or negative will assume the default value;
	After this number of failed tries, an error is logged and the local index should be considered
	stale and needs to be investigated and manually reindexed.
	Defaults to 2.

	```index.initialDelay```
	: The initial delay, internally converted in milliseconds, of triggering the
	indexing operation after the indexing even has been received.
	Typically needed when there is a well-known latency of propagation of the updates
	across the nodes sharing the same NFS volume.
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	Defaults to 0 milliseconds, meaning that indexing happens immediately when the indexing
	event is received.

	```index.retryInterval```
	: The interval of time in milliseconds between the subsequent auto-retries.
	Value is expressed in Gerrit time values as in [websession.cleanupInterval](#websessioncleanupInterval).
	Defaults to 30 seconds.

	NOTE: the default settings for `http.socketTimeout` and `http.maxTries` ensure
	that the plugin will keep retrying to forward a message for one hour.

	```websession.synchronize```
	: Whether to synchronize web sessions.
	Defaults to true.

	```websession.cleanupInterval```
	: Frequency for deleting expired web sessions. Values should use common time
	unit suffixes to express their setting:
	* s, sec, second, seconds
	* m, min, minute, minutes
	* h, hr, hour, hours
	* d, day, days
	* w, week, weeks (`1 week` is treated as `7 days`)
	* mon, month, months (`1 month` is treated as `30 days`)
	* y, year, years (`1 year` is treated as `365 days`)
	If a time unit suffix is not specified, `hours` is assumed.
	Defaults to 24 hours.

	```healthcheck.enable```
	: Whether to enable the health check endpoint. Defaults to 'true'.

	```ref-database.enabled```
	: Enable the use of a global ref-database. Defaults to 'false'.

	```ref-database.enforcementRules.<policy>```
	: Level of consistency enforcement across sites on a project:refs basis.
	Supports two values for enforcing the policy on multiple projects or refs.
	If the project or ref is omitted, apply the policy to all projects or all refs.

	The <policy> can be one of the following values:

	1. REQUIRED - Throw an exception if a git ref-update is processed against
	a local ref not yet in sync with the global ref-database.
	The user transaction is cancelled. LOCK_FAILURE is reported upstream.

	2. IGNORED - Do not validate against the global ref-database.

	Example:
	```
	[ref-database "enforcementRules"]
	IGNORED = AProject:/refs/heads/feature
	```

	Ignore the alignment with the global ref-db for AProject on refs/heads/feature.

	Defaults to no rule. All projects are REQUIRED to be consistent on all refs.