[[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. 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
  <<transport-settings-compress,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
  <<transport-settings-compression-scheme,documentation for the
  `transport.compression_scheme` setting>> for further information.

[[remote-cluster-credentials-setting]]
`cluster.remote.<cluster_alias>.credentials`::

  (<<secure-settings,Secure>>, <<reloadable-secure-settings,Reloadable>>)
  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.
