The remote clusters module allows establishing uni-directional connections to a remote cluster. This functionality is used in 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, for instance:
cluster:
remote:
cluster_one: (1)
seeds: 127.0.0.1:9300
cluster_two: (1)
seeds: 127.0.0.1:9301
-
cluster_one
andcluster_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 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 (1)
}
}
}
}
}
-
cluster_three
would be removed from the cluster settings, leavingcluster_one
andcluster_two
intact.
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.ping_schedule
-
Schedule a regular application-level ping message to ensure that transport connections to nodes belonging to remote clusters are kept alive. Defaults to
5s
, it can be set to-1
to disable pings. 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 ifcluster.remote.node.attr
is set togateway
. 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 tofalse
(defaults totrue
) 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 totrue
.
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.