Elasticsearch discovery is the process by which Elasticsearch nodes discover and communicate with each other in a cluster. Elasticsearch uses a dynamic discovery mechanism that allows nodes to discover each other automatically, without the need for manual configuration.
When a node starts up, it joins the cluster by contacting one or more existing nodes and asking for information about the cluster. The existing nodes respond with information about the other nodes in the cluster, including their IP addresses, network settings, and other configuration details.
The discovery process is based on a discovery plugin, which is a module that implements the discovery protocol and provides node discovery and communication services. Elasticsearch includes several built-in discovery plugins, including the Zen Discovery plugin, the AWS Discovery plugin, and the GCE Discovery plugin.
The Zen Discovery plugin is the default discovery plugin used by Elasticsearch. It uses a multicast protocol to discover other nodes on the network, and it can also use unicast to discover nodes that are not reachable through multicast. The AWS Discovery plugin and GCE Discovery plugin are designed for use on cloud-based infrastructure, and they use cloud-specific APIs to discover and communicate with other nodes.
In addition to the built-in discovery plugins, Elasticsearch also supports custom discovery plugins that can be developed and deployed to meet specific requirements. Custom discovery plugins can be used to integrate with custom network topologies or to provide additional features like security or fault tolerance.
Overall, Elasticsearch discovery is a key component of the Elasticsearch cluster architecture, providing automatic node discovery and communication services that make it easy to scale and manage Elasticsearch clusters. By using the dynamic discovery mechanism and built-in or custom discovery plugins, you can easily set up and manage Elasticsearch clusters in a wide range of environments.