This Docker image provides an easily configurable Elasticsearch node. Via
port mappings, it is easy to create an arbitrarily sized cluster of
nodes. As long as the versions match, you can mix-and-match "real"
Elasticsearch nodes with container-ized ones.

# Basic Usage

To start an Elasticsearch data node that listens on the standard ports on
your host's network interface:

    docker run -d -p 9200:9200 -p 9300:9300 itzg/elasticsearch

You'll then be able to connect to the Elasticsearch HTTP interface to confirm
it's alive:

http://DOCKERHOST:9200/

    {
      "status" : 200,
      "name" : "Charon",
      "version" : {
        "number" : "1.3.5",
        "build_hash" : "4a50e7df768fddd572f48830ae9c35e4ded86ac1",
        "build_timestamp" : "2014-11-05T15:21:28Z",
        "build_snapshot" : false,
        "lucene_version" : "4.9"
      },
      "tagline" : "You Know, for Search"
    }

Where `DOCKERHOST` would be the actual hostname of your host running
Docker.

# Basic multi-node cluster

Running a multi-node cluster (3-node in this example) is almost as easy:

    docker run -d -p 9200:9200 -p 9300:9300 itzg/elasticsearch
    docker run -d -p 9201:9200 -p 9301:9300 itzg/elasticsearch
    docker run -d -p 9202:9200 -p 9302:9300 itzg/elasticsearch

where the only difference was the host port binding of `9200:`/`9300:`,
`9201:`/`9301:`, and `9202:`/`9302:`. By default, Elasticsearch uses
[Zen Discovery](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-discovery-zen.html), so the three nodes find each other and form a cluster. You
can confirm that by checking the cluster health for the presence of
three nodes (`number_of_nodes`):

http://DOCKERHOST:9200/_cluster/health?pretty

    {
      "cluster_name" : "elasticsearch",
      "status" : "green",
      "timed_out" : false,
      "number_of_nodes" : 3,
      "number_of_data_nodes" : 3,
      "active_primary_shards" : 0,
      "active_shards" : 0,
      "relocating_shards" : 0,
      "initializing_shards" : 0,
      "unassigned_shards" : 0
    }

# Configuration

The following configuration options are specified using `docker run`
environment variables (`-e`) like

    docker run ... -e NAME=VALUE ... itzg/elasticsearch

## Cluster Name

If joining a pre-existing cluster, then you may need to specify a cluster name
different than the default "elasticsearch":

    -e CLUSTER=dockers

## Zen Unicast Hosts

When joining a multi-physical-host cluster, multicast may not be supported
on the physical network. In that case, your node can reference specific one or more hosts in
the cluster via the
[Zen Unicast Hosts](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-discovery-zen.html#unicast) capability as a comma-separated list of `HOST:PORT` pairs:

    -e UNICAST_HOSTS=HOST:PORT[,HOST:PORT]

such as

    -e UNICAST_HOSTS=192.168.0.100:9300

## Plugins

You can install one or more plugins before startup by passing a comma-separated
list of plugins.

    -e PLUGINS=ID[,ID]

In this example, it will install the Marvel plugin

    -e PLUGINS=elasticsearch/marvel/latest

Many more plugins [are available here](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-plugins.html#known-plugins).

## Publish As

Since the container gives the Elasticsearch software an isolated perspective
of its networking, it will most likely advertise its published address with
a container-internal IP address. This can be overridden with a physical networking
name and port using:

    -e PUBLISH_AS=DOCKERHOST:9301

_Author Note: I have yet to hit a case where this was actually necessary. Other
than the cosmetic weirdness in the logs, Elasticsearch seems to be quite tolerant._

## Node Name

Rather than use the randomly assigned node name, you can indicate a specific
one using:

    -e NODE_NAME=Docker