In the previous recipe, we saw how to create a REST entry-point, but to execute the action at cluster level, we will need to create a cluster action.
An Elasticsearch action is generally executed and distributed in the cluster and in this recipe we will see how to implement this kind of action. The cluster action will be very bare; we send a string with a value to every shard and the shards echo a result string concatenating the string with the shard number.
You need an up-and-running Elasticsearch installation as we described in the Downloading and installing Elasticsearch recipe in Chapter 2, Downloading and Setup.
A Maven tool, or an IDE that support Java programming, such as Eclipse or IntelliJ IDEA. The code for this recipe is available in the chapter17/rest_plugin directory.
