[[modules-remote-clusters]] == Remote clusters ifndef::include-xpack[] The _remote clusters_ module allows establishing uni-directional connections to a remote cluster. This functionality is used in <>. endif::[] ifdef::include-xpack[] The _remote clusters_ module allows establishing uni-directional connections to a remote cluster. This functionality is used in cross-cluster replication, and <>. endif::[] 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 <>). 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. [float] [[configuring-remote-clusters]] === Configuring Remote Clusters Remote clusters can be specified globally using <> (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 <> 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, for instance: [source,yaml] -------------------------------- cluster: remote: cluster_one: <1> seeds: 127.0.0.1:9300 cluster_two: <1> seeds: 127.0.0.1:9301 -------------------------------- <1> `cluster_one` and `cluster_two` are arbitrary _cluster aliases_ representing the connection to each cluster. These names are subsequently used to distinguish between local and remote indices. The equivalent example using the <> to add remote clusters to all nodes in the cluster would look like the following: [source,js] -------------------------------- 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" ] } } } } } -------------------------------- // CONSOLE // TEST[setup:host] // TEST[s/127.0.0.1:9300/\${transport_host}/] A remote cluster can be deleted from the cluster settings by setting its seeds to `null`: [source,js] -------------------------------- PUT _cluster/settings { "persistent": { "cluster": { "remote": { "cluster_three": { "seeds": null <1> } } } } } -------------------------------- // CONSOLE // TEST[continued] <1> `cluster_three` would be removed from the cluster settings, leaving `cluster_one` and `cluster_two` intact. [float] [[remote-cluster-settings]] === Remote cluster settings `cluster.remote.connections_per_cluster`:: The number of gateway nodes to connect to per remote cluster. The default is `3`. `cluster.remote.initial_connect_timeout`:: The time to wait for remote connections to be established when the node starts. The default is `30s`. `cluster.remote.node.attr`:: A node attribute to filter out nodes that are eligible as a gateway node in the remote cluster. For instance a node can have a node attribute `node.attr.gateway: true` such that only nodes with this attribute will be connected to if `cluster.remote.node.attr` is set to `gateway`. `cluster.remote.connect`:: By default, any node in the cluster can act as a cross-cluster client and connect to remote clusters. The `cluster.remote.connect` setting can be set to `false` (defaults to `true`) to prevent certain nodes from connecting to remote clusters. Remote cluster requests must be sent to a node that is allowed to act as a cross-cluster client. `cluster.remote.${cluster_alias}.skip_unavailable`:: Per cluster boolean setting that allows to skip specific clusters when no nodes belonging to them are available and they are the targetof a remote cluster request. Default is `false`, meaning that all clusters are mandatory by default, but they can selectively be made optional by setting this setting to `true`. `cluster.remote.${cluster_alias}.transport.ping_schedule`:: Sets the time interval between regular application-level ping messages that are sent to ensure that transport connections to nodes belonging to remote clusters are kept alive. If set to `-1`, application-level ping messages to this remote cluster are not sent. If unset, application-level ping messages are sent according to the global `transport.ping_schedule` setting, which defaults to ``-1` meaning that pings are not sent. `cluster.remote.${cluster_alias}.transport.compress`:: Per cluster boolean setting that enables you to configure compression for requests to a specific remote cluster. This setting impacts only requests sent to the remote cluster. If the inbound request is compressed, Elasticsearch compresses the response. If unset, the global `transport.compress` is used as the fallback setting. [float] [[retrieve-remote-clusters-info]] === Retrieving remote clusters info The <> allows to retrieve information about the configured remote clusters, as well as the remote nodes that the node is connected to.