Creating a cluster action

In the previous recipe, we saw how to create a REST entry point, but to execute the action at the 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.

Getting ready

You need an up and running Elasticsearch installation, as we described in the Downloading and installing Elasticsearch recipe in Chapter 1, Getting Started.

Gradle or an integrated development environment (IDE) that supports Java programming with Gradle (version 7.3.x used in the examples), such as Eclipse, Visual Studio Code, or IntelliJ IDEA, is required. Java JDK 17 or above needs to be installed.

The code for this recipe is available in the ch16/rest_plugin directory...