Elasticsearch Changes Feed Plugin

A plugin for elasticsearch which allows a client to create a websocket connection to an elasticsearch node and receive a feed of changes from the database.

Loosely based on https://github.com/derryx/elasticsearch-changes-plugin

Requirements

• Elasticsearch 1.x, 2.x, 5.x, 6.x
• Java 8+

Prebuilt Binary Installation

To install run the following command, replacing {version} with the version you want to install, e.g. v2.2.0. Note that the plugin requires additional permissions which will automatically be granted using the below command (remove -b option if you want to manually approve these permissions)

bin/elasticsearch-plugin install -b https://github.com/ForgeRock/es-change-feed-plugin/releases/download/{version}/es-changes-feed-plugin.zip

Restart elasticsearch.

Note that Elasticsearch plugins have to be built for the exact version of Elasticsearch which they are to be installed in. If a prebuilt binary isn't available for your version of Elasticsearch, then you'll need to build from source.

Build From Source

git clone https://github.com/ForgeRock/es-change-feed-plugin.git
cd es-change-feed-plugin

Update the version and elasticsearch.version property in the pom.xml. Then to build:

mvn clean install

Troubleshooting

When changing the version you may run into problems when the Elasticsearch API changes. Try taking the nearest branch to the version you're trying to build for.

Limitations

There is a good explanation here of some of the difficulties inherent in a changes feed from elasticsearch: https://groups.google.com/d/msg/elasticsearch/S3fSfr4Cz3g/fyse5X4ofuYJ

This plugin has the following limitations:

• Only sends live changes - if the client isn't connected at the time the plugin gets the change, it won't be sent
• Doesn't send the initial state of any documents. You need to use one of the existing APIs for this
• No handling of misbehaving endpoints beyond what the underlying websocket implementation does see Project Tyrus
• Client needs to handle failing nodes

Configuration

changes.port

Port the websocket will use. Default is 9400

changes.listenSource

Which indices, types and documents the plugin will listen to in the format <index_pattern>[/<type_pattern>[/<document_pattern>]].

Each of the above patterns is can be either:

• * All indices, types or documents
• id[,id]* List of specific indices, types or documents

So for example:

* will match everything. This is the default value

*/tweet/* will match all tweets in any index

gb,us/user,tweet/* will match all documents of type user or tweet in the gb or us indices

changes.disable

Disable the plugin through config. Setting this to true will stop the websocket server from starting up and will not intercept and change requests.

Messages

The websocket will be on the path /ws/_changes. When you connect, you should start receiving messages which look something like this:

{
    "_id": "testdoc",
    "_index": "testidx",
    "_operation": "INDEX",
    "_source": {
        "hello": "world"
    },
    "_timestamp": "2015-10-23T14:22:44.738Z",
    "_type": "testtyp",
    "_version": 1
}