Remote clusters

The remote clusters module enables you to establish uni-directional connections to a remote cluster. This functionality is used in cross-cluster replication and cross-cluster search.

Remote cluster connections work by configuring a remote cluster and connecting only to a limited number of nodes in the remote cluster. Each remote cluster is referenced by a name and a list of seed nodes. When a remote cluster is registered, its cluster state is retrieved from one of the seed nodes so that by default up to three gateway nodes are selected to be connected to as part of remote cluster requests. Remote cluster connections consist of uni-directional connections from the coordinating node to the previously selected remote nodes only. It is possible to tag which nodes should be selected through node attributes (see Remote cluster settings).

Each node in a cluster that has remote clusters configured connects to one or more gateway nodes and uses them to federate requests to the remote cluster.

Remote clusters can be specified globally using cluster settings (which can be updated dynamically), or local to individual nodes using the elasticsearch.yml file.

If a remote cluster is configured via elasticsearch.yml only the nodes with that configuration will be able to connect to the remote cluster. In other words, functionality that relies on remote cluster requests will have to be driven specifically from those nodes. Remote clusters set via the cluster settings API will be available on every node in the cluster.

The elasticsearch.yml config file for a node that connects to remote clusters needs to list the remote clusters that should be connected to. The format for each seeds entry is remote_host:transport.tcp.port, for instance:

cluster:
    remote:
        cluster_one: 
            seeds: 127.0.0.1:9301
        cluster_two: 
            seeds: 127.0.0.1:9302

The equivalent example using the cluster settings API to add remote clusters to all nodes in the cluster would look like the following:

PUT _cluster/settings
{
  "persistent": {
    "cluster": {
      "remote": {
        "cluster_one": {
          "seeds": [
            "127.0.0.1:9300"
          ]
        },
        "cluster_two": {
          "seeds": [
            "127.0.0.1:9301"
          ]
        },
        "cluster_three": {
          "seeds": [
            "127.0.0.1:9302"
          ]
        }
      }
    }
  }
}

A remote cluster can be deleted from the cluster settings by setting its seeds to null:

PUT _cluster/settings
{
  "persistent": {
    "cluster": {
      "remote": {
        "cluster_three": {
          "seeds": null 
        }
      }
    }
  }
}

The Remote Cluster Info API allows to retrieve information about the configured remote clusters, as well as the remote nodes that the node is connected to.