Multicast discovery is a mechanism that allows Elasticsearch nodes to discover and communicate with each other using multicast communication. Multicast discovery is the default discovery mechanism used by Elasticsearch, and it is used when networking infrastructure supports multicast.
In multicast discovery, each node in the cluster sends a multicast request to a specific multicast address and port. The request includes information about the node, such as its IP address, hostname, and other configuration details.
When other nodes receive the multicast request, they respond with information about themselves, and they also include information about other nodes that they know about. This allows nodes to build a complete view of the cluster topology and to communicate with other nodes in the cluster.
Multicast discovery is often used in network environments where nodes are located on the same subnet and multicast communication is allowed and practical. It is a simple and efficient mechanism for discovering and communicating with other nodes in the cluster.
To configure multicast discovery in Elasticsearch, you can specify the multicast address and port in the `discovery.zen.ping.multicast.address` and `discovery.zen.ping.multicast.port` settings in the Elasticsearch configuration file. For example, to use the multicast address `239.193.0.1` and port `9300`, you can add the following lines to the configuration file:
discovery.zen.ping.multicast.enabled: true discovery.zen.ping.multicast.address: 239.193.0.1 discovery.zen.ping.multicast.port: 9300
Overall, multicast discovery is a key mechanism for discovering and communicating with nodes in an Elasticsearch cluster, and it is used in a wide range of environments where multicast communication is available and practical.