How to write ElasticSearch 2.2 plugin, Getting start Elasticsearch Plugin, Develop ElasticSearch Plugin, How to debug elasticsearch plugin using eclipse, Remote debuging in Elasticsearch plugin, first plugin in Elasticsearch,

How to develop custom plugin for ElasticSearch 2.2

What is Plugin:
Plugins are a way to enhance the basic elasticsearch functionality in a custom manner. They range from adding custom mapping types, custom analyzers, native scripts, custom discovery and more.

There are three types of plugins:
- Java plugins
    These plugins contain only JAR files, and must be installed on every node in the cluster. After installation, each node must be restarted before the plugin becomes visible.
- Site plugins
    These plugins contain static web content like Javascript, HTML, and CSS files, that can be served directly from Elasticsearch.
    http://yournode:9200/_plugin/[plugin name]
- Mixed plugins
  Mixed plugins contain both JAR files and web content.

Here, I am going to develop Java Plugins.
1. Create one simple Maven project from Eclipse.
2. Add below things to your pom.xml
  
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.elasticsearch</groupId>
  <artifactId>es_plugin</artifactId>
  <version>1.1</version>
  <packaging>jar</packaging>

  <name>es_plugin</name>


  <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

  <dependencies>
    <dependency>
             <groupId>org.elasticsearch</groupId>
            <artifactId>elasticsearch</artifactId>
            <version>2.2.1</version>
            <scope>provided</scope>
        </dependency>
     </dependencies>
   
     <build>
    <finalName>${project.artifactId}</finalName>
        <plugins>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.5.5</version>
                <configuration>
                    <appendAssemblyId>false</appendAssemblyId>
                    <outputDirectory>${project.build.directory}/releases/</outputDirectory>
                    <descriptors>
                        <descriptor>${basedir}/src/main/assemblies/plugin.xml</descriptor>
                    </descriptors>
                </configuration>
                </plugin>
</plugins>
    </build>
 
</project>

   

3. In side src folder, you should have these three folders.
  src -> assemblies, java and resources subfolder
4. Inside assemblies folder, plugin.xml
5. Inside resources, plugin-descriptor.properties file should be there.
6. Inside java folder, all java file under package, In my case
   java\org\elasticsearch\es_plugin this folder has three java file.
   - App.java
   - ExampleRestModule.java
   - HelloRestHandler.java
 
** plugin.xml **

  <?xml version="1.0"?>
<assembly
    xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 http://maven.apache.org/xsd/assembly-1.1.2.xsd">
    <id>plugin</id>
    <formats>
        <format>zip</format>
    </formats>
    <includeBaseDirectory>false</includeBaseDirectory>
    <dependencySets>
        <dependencySet>
            <outputDirectory>/</outputDirectory>
            <useProjectArtifact>true</useProjectArtifact>
            <useTransitiveFiltering>true</useTransitiveFiltering>
        </dependencySet>
    </dependencySets>
</assembly>


** plugin-descriptor.properties **

# All plugins, be they site or Java plugins, must contain a file called plugin-descriptor.properties in the root directory.
# Elasticsearch plugin descriptor file
description=Binod Suman ES Demo Plugin
version=1.1
# 'name': the plugin name
name=Binod ES Plugin Demo
jvm=true
# 'classname': the name of the class to load, fully-qualified.
#classname=com.netiq.scm.SCMPlugin
classname=org.elasticsearch.es_plugin.App
java.version=1.8
elasticsearch.version=2.2.1

** App.java **
package org.elasticsearch.es_plugin;

import java.util.Collection;
import java.util.Collections;

import org.elasticsearch.common.inject.Module;
import org.elasticsearch.plugins.Plugin;

@SuppressWarnings("static-method")
public class App extends Plugin {

    @Override
public String name() {
return "Binod Suman ElasticSearch Demo Name";
}

@Override
public String description() {
return "** Purpose for this plugin to how to write first ElasticSearch Demo";
}


@Override
    public Collection nodeModules() {
        return Collections.singletonList(new ExampleRestModule());
    }
}


** ExampleRestModule.java **
package org.elasticsearch.es_plugin;

import org.elasticsearch.common.inject.AbstractModule;

public class ExampleRestModule extends AbstractModule {

@Override
protected void configure() {
bind(HelloRestHandler.class).asEagerSingleton();
}

 }

 ** HelloRestHandler.java **
package org.elasticsearch.es_plugin;

import org.elasticsearch.common.component.AbstractComponent;
import org.elasticsearch.common.inject.Inject;
import org.elasticsearch.common.settings.Settings;

public class HelloRestHandler extends AbstractComponent  {

@Inject
public HelloRestHandler(Settings settings) {
super(settings);
System.out.println("**** Hello I am here in HelloResthandler Module of ES 2 **");
}



}

** Now build your code by pom.xml **
mvn clean install
It will create one jar file "es_plugin.jar" inside target folder.

Create one folder in side your ElasticSearch installation Plugin folder. In my case, I created one folder
binod-demo-plugin inside E:\Software\elasticsearch-2.2.1\plugins folder.
Inside E:\Software\elasticsearch-2.2.1\plugins\binod-demo-plugin folder, I kept these two files:
 es_plugin.jar
 plugin-descriptor.properties

Now try to restart ElasticSearch.
E:\Software\elasticsearch-2.2.1\bin>elasticsearch.bat
[2016-03-22 23:03:38,140][INFO ][node                     ] [Bison] version[2.2.1], pid[13000], build[d045fc2/2016-03-09T09:38:54Z]
[2016-03-22 23:03:38,141][INFO ][node                     ] [Bison] initializing ...
[2016-03-22 23:03:38,689][INFO ][plugins                  ] [Bison] modules [lang-expression, lang-groovy], plugins [Binod ES Plugin Demo, scm], sites []
[2016-03-22 23:03:38,712][INFO ][env                      ] [Bison] using [1] data paths, mounts [[New Volume (E:)]], net usable_space [66.1gb], net total_space [157.8gb], spins? [unknown], types [NTFS]
[2016-03-22 23:03:38,712][INFO ][env                      ] [Bison] heap size [910.5mb], compressed ordinary object pointers [true]
[2016-03-22 23:03:38,931][INFO ][http                     ] [Bison] Using [org.elasticsearch.http.netty.NettyHttpServerTransport] as http transport, overridden by [SCM]
**** Hello I am here in HelloResthandler Module of ES 2 **
[2016-03-22 23:03:39,779][INFO ][com.netiq.scm.Util       ] [Bison] java.home = D:\InstalledFolder\Java\jdk1.8.0_45\jre
[2016-03-22 23:03:39,780][ERROR][com.netiq.scm.Util       ] [Bison] E:\Software\elasticsearch-2.2.1\config\db.properties (The system cannot find the file specified)
[2016-03-22 23:03:40,878][ERROR][com.netiq.scm.Util       ] [Bison] Cannot sync configuration from SCM Core. java.net.MalformedURLException: no protocol: nullconfig/[get]
[2016-03-22 23:03:40,997][INFO ][node                     ] [Bison] initialized
[2016-03-22 23:03:40,997][INFO ][node                     ] [Bison] starting ...
-03-22 23:03:47,695][INFO ][node                     ] [Bison] started

Here you can see the output carefully, some message comes from your own plugin.
 
**** How to set Debug breakpoint  *****
1. put break point of HelloRestHandler constructor
2. Add some extra parameter in elasticsearch.bat file.
   For More details: http://binodsuman.blogspot.in/2016/03/how-to-call-elasticsearch-in-debug-mode.html
3. Set one remote debug for this project in Eclipse.
4. Now start ElasticSearch.bat with extra debug parameter and start project in Eclipse.