Remote cluster settings

The following settings apply to both sniff mode and proxy mode. Settings that are specific to sniff mode and proxy mode are described separately.

cluster.remote.<cluster_alias>.mode: The mode used for a remote cluster connection. The only supported modes are sniff and proxy. The default is sniff. See Connection modes for further information about these modes, and Sniff mode remote cluster settings and Proxy mode remote cluster settings for further information about their settings.
cluster.remote.initial_connect_timeout: The time to wait for remote connections to be established when the node starts. The default is 30s.
remote_cluster_client role: By default, any node in the cluster can act as a cross-cluster client and connect to remote clusters. To prevent a node from connecting to remote clusters, specify the node.roles setting in elasticsearch.yml and exclude remote_cluster_client from the listed roles. Search requests targeting remote clusters must be sent to a node that is allowed to act as a cross-cluster client. Other features such as machine learning data feeds, transforms, and cross-cluster replication require the remote_cluster_client role.
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 target of a remote cluster request.

In Elasticsearch 8.15, the default value for skip_unavailable was changed from false to true. Before Elasticsearch 8.15, if you want a cluster to be treated as optional for a cross-cluster search, then you need to set that configuration. From Elasticsearch 8.15 forward, you need to set the configuration in order to make a cluster required for the cross-cluster search. Once you upgrade the local ("querying") cluster search coordinator node (the node you send CCS requests to) to 8.15 or later, any remote clusters that do not have an explicit setting for skip_unavailable will immediately change over to using the new default of true. This is true regardless of whether you have upgraded the remote clusters to 8.15, as the skip_unavailable search behavior is entirely determined by the setting on the local cluster where you configure the remotes.

cluster.remote.<cluster_alias>.transport.ping_schedule: Sets the time interval between regular application-level ping messages that are sent to try and keep remote cluster connections 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. It is preferable to correctly configure TCP keep-alives instead of configuring a ping_schedule, because TCP keep-alives are handled by the operating system and not by Elasticsearch. By default Elasticsearch enables TCP keep-alives on remote cluster connections. Remote cluster connections are transport connections so the transport.tcp.* advanced settings regarding TCP keep-alives apply to them.
cluster.remote.<cluster_alias>.transport.compress: Per-cluster setting that enables you to configure compression for requests to a specific remote cluster. The handling cluster will automatically compress responses to compressed requests. The setting options are true, indexing_data, and false. If unset, defaults to the behaviour specified by the node-wide transport.compress setting. See the documentation for the transport.compress setting for further information.
cluster.remote.<cluster_alias>.transport.compression_scheme: Per-cluster setting that enables you to configure the compression scheme for requests to a specific cluster if those requests are selected to be compressed by to the cluster.remote.<cluster_alias>.transport.compress setting. The handling cluster will automatically use the same compression scheme for responses as for the corresponding requests. The setting options are deflate and lz4. If unset, defaults to the behaviour specified by the node-wide transport.compression_scheme setting. See the documentation for the transport.compression_scheme setting for further information.

cluster.remote.<cluster_alias>.credentials: (Secure, Reloadable) Per-cluster setting for configuring remote clusters with the API Key based model. This setting takes the encoded value of a cross-cluster API key and must be set in the Elasticsearch keystore on each node in the cluster. The presence (or not) of this setting determines which model a remote cluster uses. If present, the remote cluster uses the API key based model. Otherwise, it uses the certificate based model. If the setting is added, removed, or updated in the Elasticsearch keystore and reloaded via the Nodes reload secure settings API, the cluster will automatically rebuild its connection to the remote.

Sniff mode remote cluster settings

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To use sniff mode to connect to a remote cluster, set cluster.remote.<cluster_alias>.mode: sniff and then configure the following settings. You may also leave cluster.remote.<cluster_alias>.mode unset since sniff is the default mode.

cluster.remote.<cluster_alias>.seeds: The list of seed nodes used to sniff the remote cluster state.
cluster.remote.<cluster_alias>.node_connections: The number of gateway nodes to connect to for this remote cluster. The default is 3.

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.

Proxy mode remote cluster settings

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To use proxy mode to connect to a remote cluster, set cluster.remote.<cluster_alias>.mode: proxy and then configure the following settings.

cluster.remote.<cluster_alias>.proxy_address: The address used for all remote connections.
cluster.remote.<cluster_alias>.proxy_socket_connections: The number of socket connections to open per remote cluster. The default is 18.

cluster.remote.<cluster_alias>.server_name: An optional hostname string which is sent in the server_name field of the TLS Server Name Indication extension if TLS is enabled. The TLS transport will fail to open remote connections if this field is not a valid hostname as defined by the TLS SNI specification.

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