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Ref guide: add license to cluster-plugins.adoc; fix section title case throughout
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Cassandra Targett
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@ -1,15 +1,29 @@
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= Cluster Plugins
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:toc: macro
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:toclevels: 3
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// Licensed to the Apache Software Foundation (ASF) under one
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// or more contributor license agreements. See the NOTICE file
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// distributed with this work for additional information
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// regarding copyright ownership. The ASF licenses this file
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// to you under the Apache License, Version 2.0 (the
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// "License"); you may not use this file except in compliance
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// with the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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toc::[]
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== Cluster (CoreContainer-level) plugins subsystem
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== Cluster (CoreContainer-level) Plugins Subsystem
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Cluster plugins are pluggable components that are defined and instantiated at the
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`CoreContainer` (node) level. These components usually provide admin-level functionality
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and APIs for additional functionality at the Solr node level.
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=== Plugin configurations
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=== Plugin Configurations
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Plugin configurations are maintained using `/cluster/plugin` API.
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This API endpoint allows adding, removing and updating plugin configurations.
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@ -29,7 +43,7 @@ The following common plugin properties are supported:
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`name`::
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(required) unique plugin name. Some plugin types require using one of the
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pre-defined names to properly function. By convention such predefined names use
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a leading-dot prefix (e.g. `.placement-plugin`)
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a leading-dot prefix (e.g., `.placement-plugin`)
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`class`::
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(required) implementation class. This can be specified as a fully-qualified
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@ -60,7 +74,7 @@ curl -X POST -H 'Content-type: application/json' -d '{
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http://localhost:8983/api/cluster/plugin
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----
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=== Types of cluster plugins
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=== Types of Cluster Plugins
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Classes loaded from plugins in general support two types of functionality (not mutually exclusive):
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* request handler plugins that expose REST API endpoints (the implementing class is annotated with
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@ -72,22 +86,22 @@ automatically discovered and registered with sub-systems that use this type of p
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include the `ClusterSingleton`, ClusterEventProducer`, `ClusterEventListener`
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and `PlacementPluginFactory`.
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=== Plugin life-cycle
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=== Plugin Lifecycle
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Plugin instances are loaded and initialized when Solr's `CoreContainer` is first created during
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Solr node start-up.
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Then on each update of the configurations each node is notified about the change,
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and then the existing plugins are compared with the new configs, and plugin instances
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present on the node are respectively created, removed, or
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replaced (i.e. removed and added using the new configuration).
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replaced (i.e., removed and added using the new configuration).
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In practice this means that cluster-level plugins managed by this API can be
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dynamically changed and reconfigured without restarting the Solr nodes, and the changes
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apply to all nodes nearly simultaneously.
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== Plugin types
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== Plugin Types
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=== Predefined plugin names
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=== Predefined Plugin Names
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Plugins with these names are used in specific parts of Solr. Their names are reserved
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and cannot be used for other plugin types:
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@ -100,11 +114,11 @@ determines the replica placement strategy in the cluster.
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plugin that implements `ClusterEventProducer` interface. This type of plugin
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is used for generating cluster-level events.
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=== PlacementPluginFactory plugins
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=== PlacementPluginFactory Plugins
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This type of plugin supports configurable placement strategies for collection
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replicas.
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=== ClusterSingleton plugins
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=== ClusterSingleton Plugins
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Plugins that implement `ClusterSingleton` interface are instantiated on each
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Solr node. However, their start/stop life-cycle, as defined in the interface,
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is controlled in such a way that only a single running instance of the plugin
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@ -116,7 +130,7 @@ is present in the cluster at any time.
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Any plugin can implement this interface to indicate to Solr that
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it requires this cluster singleton behavior.
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=== ClusterEventProducer plugin
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=== ClusterEventProducer Plugins
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In order to support the generation of cluster-level events an implementation of
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`ClusterEventProducer` is created on each Solr node. This component is also a
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`ClusterSingleton`, which means that only one active instance is present in the
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@ -152,7 +166,7 @@ curl -X POST -H 'Content-type: application/json' -d '{
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----
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=== ClusterEventListener plugins
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=== ClusterEventListener Plugins
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Plugins that implement the `ClusterEventListener` interface will be automatically
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registered with the instance of `ClusterEventProducer`.
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@ -181,9 +195,9 @@ curl -X POST -H 'Content-type: application/json' -d '{
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http://localhost:8983/api/cluster/plugin
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----
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== Plugin management API
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== Plugin Management API
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=== List plugins
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=== List Plugins
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This command uses HTTP GET and returns a list of loaded plugins and their configurations:
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[source,bash]
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@ -191,7 +205,7 @@ This command uses HTTP GET and returns a list of loaded plugins and their config
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curl http://localhost:8983/api/cluster/plugin
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----
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=== Add plugin
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=== Add Plugin
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This command uses HTTP POST to add a new plugin configuration. If a plugin with the
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same name already exists this results in an error.
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@ -207,7 +221,7 @@ curl -X POST -H 'Content-type: application/json' -d '{
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http://localhost:8983/api/cluster/plugin
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----
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=== Update plugin
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=== Update Plugin
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This command uses HTTP POST to update an existing plugin configuration. If a plugin
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with this name doesn't exist this results in an error.
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@ -226,7 +240,7 @@ curl -X POST -H 'Content-type: application/json' -d '{
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http://localhost:8983/api/cluster/plugin
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----
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=== Remove plugin
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=== Remove Plugin
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This command uses HTTP POST to delete an existing plugin configuration. If a plugin
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with this name doesn't exist this results in an error.
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