[[remote-clusters-settings]]
=== Remote cluster settings
The following settings apply to both <<sniff-mode,sniff mode>> and
<<proxy-mode,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`.

`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` <<node-roles,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,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 {ml} <<general-ml-settings,data
  feeds>>, <<general-transform-settings,transforms>>, and
  <<ccr-getting-started-tutorial,{ccr}>> 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.

IMPORTANT: 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 {ccs}, 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 {ccs}. 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 {es}. By default {es} enables TCP keep-alives on
  remote cluster connections. Remote cluster connections are transport
  connections so the `transport.tcp.*` <<transport-settings,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. This setting impacts only requests
  sent to the remote cluster. If the inbound request is compressed,
  Elasticsearch compresses the response. The setting options are `true`,
  `indexing_data`, and `false`. If unset, the global `transport.compress` is
  used as the fallback setting.

`cluster.remote.<cluster_alias>.transport.compression_scheme`::

  Per cluster setting that enables you to configure compression scheme for
  requests to a specific remote cluster. This setting impacts only requests
  sent to the remote cluster. If an inbound request is compressed, {es}
  compresses the response using the same compression scheme. The setting options
  are `deflate` and `lz4`. If unset, the global `transport.compression_scheme`
  is used as the fallback setting.


`cluster.remote.<cluster_alias>.credentials` (<<secure-settings,Secure>>, <<reloadable-secure-settings,Reloadable>>)::
[[remote-cluster-credentials-setting]]

  Per cluster setting for configuring <<remote-clusters-api-key,remote clusters with the API Key based model>>.
  This setting takes the encoded value of a
  <<security-api-create-cross-cluster-api-key,cross-cluster API key>> and must be set
  in the <<secure-settings,{es} 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 <<secure-settings,{es} keystore>> and reloaded via the
  <<cluster-nodes-reload-secure-settings>> API, the cluster will automatically rebuild its connection to the remote.

[[remote-cluster-sniff-settings]]
==== Sniff mode remote cluster settings

`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]]
`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`.

[[remote-cluster-proxy-settings]]
==== Proxy mode remote cluster 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`.

[role="xpack"]
`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
  <<encrypt-internode-communication,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.
