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68db1fd780
Today the docs for remote cluster connections use `ping_schedule` fairly liberally, and don't mention that you should prefer TCP keepalives wherever possible. This commit reduces the use of this setting in the examples and adjusts the description of the setting to include a note about TCP keepalives instead.
338 lines
12 KiB
Text
338 lines
12 KiB
Text
[[modules-remote-clusters]]
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== Remote clusters
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You can connect a local cluster to other {es} clusters, known as _remote
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clusters_. Once connected, you can search remote clusters using
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<<modules-cross-cluster-search,{ccs}>>. You can also sync data between clusters
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using <<xpack-ccr,{ccr}>>.
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To register a remote cluster, connect the local cluster to nodes in the
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remote cluster using one of two connection modes:
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* <<sniff-mode,Sniff mode>>
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* <<proxy-mode,Proxy mode>>
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Your local cluster uses the <<modules-network,transport layer>> to establish
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communication with remote clusters. The coordinating nodes in the local cluster
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establish <<long-lived-connections,long-lived>> TCP connections with specific
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nodes in the remote cluster. {es} requires these connections to remain open,
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even if the connections are idle for an extended period.
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You can use the <<cluster-remote-info, remote cluster info API>> to get
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information about registered remote clusters.
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[[sniff-mode]]
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[discrete]
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==== Sniff mode
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In sniff mode, a cluster is created using a name and a list of seed nodes. When
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a remote cluster is registered, its cluster state is retrieved from one of the
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seed nodes and up to three _gateway nodes_ are selected as part of remote
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cluster requests. This mode requires that the gateway node's publish addresses
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are accessible by the local cluster.
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Sniff mode is the default connection mode.
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[[gateway-nodes-selection]]
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The _gateway nodes_ selection depends on the following criteria:
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* *version*: Remote nodes must be compatible with the cluster they are
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registered to, similar to the rules for
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<<rolling-upgrades>>:
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** Any node can communicate with another node on the same
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major version. For example, 7.0 can talk to any 7.x node.
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** Only nodes on the last minor version of a certain major version can
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communicate with nodes on the following major version. In the 6.x series, 6.8
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can communicate with any 7.x node, while 6.7 can only communicate with 7.0.
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** Version compatibility is
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symmetric, meaning that if 6.7 can communicate with 7.0, 7.0 can also
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communicate with 6.7. The following table depicts version compatibility between
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local and remote nodes.
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+
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[%collapsible]
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.Version compatibility table
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====
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// tag::remote-cluster-compatibility-matrix[]
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[cols="^,^,^,^,^,^,^,^"]
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|====
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| 7+^h| Local cluster
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h| Remote cluster | 5.0->5.5 | 5.6 | 6.0->6.6 | 6.7 | 6.8 | 7.0 | 7.1->7.x
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| 5.0->5.5 | {yes-icon} | {yes-icon} | {no-icon} | {no-icon} | {no-icon} | {no-icon} | {no-icon}
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| 5.6 | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {no-icon} | {no-icon}
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| 6.0->6.6 | {no-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {no-icon} | {no-icon}
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| 6.7 | {no-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {no-icon}
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| 6.8 | {no-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon}
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| 7.0 | {no-icon} | {no-icon} | {no-icon} | {yes-icon} | {yes-icon} | {yes-icon} | {yes-icon}
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| 7.1->7.x | {no-icon} | {no-icon} | {no-icon} | {no-icon} | {yes-icon} | {yes-icon} | {yes-icon}
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|====
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// end::remote-cluster-compatibility-matrix[]
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====
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* *role*: Dedicated master nodes are never selected as gateway nodes.
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* *attributes*: You can tag which nodes should be selected
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(see <<remote-cluster-settings>>), though such tagged nodes still have
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to satisfy the two above requirements.
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[[proxy-mode]]
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[discrete]
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==== Proxy mode
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In proxy mode, a cluster is created using a name and a single proxy address.
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When you register a remote cluster, a configurable number of socket connections
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are opened to the proxy address. The proxy is required to route those
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connections to the remote cluster. Proxy mode does not require remote cluster
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nodes to have accessible publish addresses.
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The proxy mode is not the default connection mode and must be configured. Similar
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to the sniff <<gateway-nodes-selection,gateway nodes>>, the remote
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connections are subject to the same version compatibility rules as
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<<rolling-upgrades>>.
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[discrete]
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[[configuring-remote-clusters]]
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=== Configuring remote clusters
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You can configure remote clusters settings <<configure-remote-clusters-dynamic,globally>>, or configure
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settings <<configure-remote-clusters-static,on individual nodes>> in the
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`elasticsearch.yml` file.
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[discrete]
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[[configure-remote-clusters-dynamic]]
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===== Dynamically configure remote clusters
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Use the <<cluster-update-settings,cluster update settings API>> to dynamically
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configure remote settings on every node in the cluster. For example:
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[source,console]
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--------------------------------
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PUT _cluster/settings
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{
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"persistent": {
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"cluster": {
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"remote": {
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"cluster_one": {
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"seeds": [
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"127.0.0.1:9300"
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]
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},
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"cluster_two": {
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"mode": "sniff",
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"seeds": [
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"127.0.0.1:9301"
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],
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"transport.compress": true,
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"skip_unavailable": true
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},
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"cluster_three": {
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"mode": "proxy",
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"proxy_address": "127.0.0.1:9302"
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}
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}
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}
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}
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}
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--------------------------------
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// TEST[setup:host]
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// TEST[s/127.0.0.1:9300/\${transport_host}/]
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You can dynamically update the compression and ping schedule settings. However,
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you must include the `seeds` or `proxy_address` in the settings update request.
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For example:
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[source,console]
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--------------------------------
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PUT _cluster/settings
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{
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"persistent": {
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"cluster": {
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"remote": {
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"cluster_one": {
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"seeds": [
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"127.0.0.1:9300"
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]
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},
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"cluster_two": {
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"mode": "sniff",
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"seeds": [
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"127.0.0.1:9301"
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],
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"transport.compress": false
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},
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"cluster_three": {
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"mode": "proxy",
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"proxy_address": "127.0.0.1:9302",
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"transport.compress": true,
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"transport.ping_schedule": "60s"
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}
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}
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}
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}
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}
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--------------------------------
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// TEST[continued]
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NOTE: When the compression or ping schedule settings change, all the existing
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node connections must close and re-open, which can cause in-flight requests to
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fail.
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You can delete a remote cluster from the cluster settings by passing `null`
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values for each remote cluster setting:
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[source,console]
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--------------------------------
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PUT _cluster/settings
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{
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"persistent": {
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"cluster": {
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"remote": {
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"cluster_two": { <1>
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"mode": null,
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"seeds": null,
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"skip_unavailable": null,
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"transport.compress": null
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}
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}
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}
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}
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}
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--------------------------------
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// TEST[continued]
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<1> `cluster_two` would be removed from the cluster settings, leaving
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`cluster_one` and `cluster_three` intact.
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[discrete]
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[[configure-remote-clusters-static]]
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===== Statically configure remote clusters
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If you specify settings in `elasticsearch.yml` files, only the nodes with
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those settings can connect to the remote cluster and serve remote cluster requests. For example:
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[source,yaml]
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--------------------------------
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cluster:
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remote:
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cluster_one: <1>
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seeds: 127.0.0.1:9300 <2>
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cluster_two: <1>
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mode: sniff <3>
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seeds: 127.0.0.1:9301 <2>
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transport.compress: true <4>
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skip_unavailable: true <5>
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cluster_three: <1>
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mode: proxy <3>
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proxy_address: 127.0.0.1:9302 <6>
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--------------------------------
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<1> `cluster_one`, `cluster_two`, and `cluster_three` are arbitrary _cluster aliases_
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representing the connection to each cluster. These names are subsequently used to
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distinguish between local and remote indices.
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<2> The hostname and <<transport-settings,transport port>> (default: 9300) of a
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seed node in the remote cluster.
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<3> The configured connection mode. By default, this is <<sniff-mode,`sniff`>>, so
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the mode is implicit for `cluster_one`. However, it can be explicitly configured
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as demonstrated by `cluster_two` and must be explicitly configured for
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<<proxy-mode,proxy mode>> as demonstrated by `cluster_three`.
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<4> Compression is explicitly enabled for requests to `cluster_two`.
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<5> Disconnected remote clusters are optional for `cluster_two`.
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<6> The address for the proxy endpoint used to connect to `cluster_three`.
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[discrete]
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[[remote-cluster-settings]]
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=== Global remote cluster settings
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These settings apply to both <<sniff-mode,sniff mode>> and
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<<proxy-mode,proxy mode>>. <<remote-cluster-sniff-settings,Sniff mode settings>>
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and <<remote-cluster-proxy-settings,proxy mode settings>> are described
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separately.
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`cluster.remote.<cluster_alias>.mode`::
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The mode used for a remote cluster connection. The only supported modes are
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`sniff` and `proxy`.
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`cluster.remote.initial_connect_timeout`::
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The time to wait for remote connections to be established when the node
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starts. The default is `30s`.
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`remote_cluster_client` <<node-roles,role>>::
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By default, any node in the cluster can act as a cross-cluster client and
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connect to remote clusters. To prevent a node from connecting to remote
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clusters, specify the <<node-roles,node.roles>> setting in `elasticsearch.yml`
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and exclude `remote_cluster_client` from the listed roles. Search requests
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targeting remote clusters must be sent to a node that is allowed to act as a
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cross-cluster client. Other features such as {ml} <<general-ml-settings,data
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feeds>>, <<general-transform-settings,transforms>>, and
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<<ccr-getting-started,{ccr}>> require the `remote_cluster_client` role.
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`cluster.remote.<cluster_alias>.skip_unavailable`::
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Per cluster boolean setting that allows to skip specific clusters when no
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nodes belonging to them are available and they are the target of a remote
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cluster request. Default is `false`, meaning that all clusters are mandatory
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by default, but they can selectively be made optional by setting this setting
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to `true`.
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`cluster.remote.<cluster_alias>.transport.ping_schedule`::
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Sets the time interval between regular application-level ping messages that
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are sent to try and keep remote cluster connections alive. If set to `-1`,
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application-level ping messages to this remote cluster are not sent. If
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unset, application-level ping messages are sent according to the global
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`transport.ping_schedule` setting, which defaults to `-1` meaning that pings
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are not sent. It is preferable to correctly configure TCP keep-alives instead
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of configuring a `ping_schedule`, because TCP keep-alives are handled by the
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operating system and not by {es}. By default {es} enables TCP keep-alives on
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remote cluster connections. Remote cluster connections are transport
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connections so the `transport.tcp.*` <<transport-settings,advanced settings>>
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regarding TCP keep-alives apply to them.
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`cluster.remote.<cluster_alias>.transport.compress`::
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Per cluster setting that enables you to configure compression for requests
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to a specific remote cluster. This setting impacts only requests
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sent to the remote cluster. If the inbound request is compressed,
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Elasticsearch compresses the response. The setting options are `true`,
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`indexing_data`, and `false`. The option `indexing_data` is experimental.
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If unset, the global `transport.compress` is used as the fallback setting.
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[discrete]
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[[remote-cluster-sniff-settings]]
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=== Sniff mode remote cluster settings
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`cluster.remote.<cluster_alias>.seeds`::
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The list of seed nodes used to sniff the remote cluster state.
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`cluster.remote.<cluster_alias>.node_connections`::
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The number of gateway nodes to connect to for this remote cluster. The default
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is `3`.
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`cluster.remote.node.attr`::
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A node attribute to filter out nodes that are eligible as a gateway node in
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the remote cluster. For instance a node can have a node attribute
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`node.attr.gateway: true` such that only nodes with this attribute will be
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connected to if `cluster.remote.node.attr` is set to `gateway`.
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[discrete]
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[[remote-cluster-proxy-settings]]
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=== Proxy mode remote cluster settings
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`cluster.remote.<cluster_alias>.proxy_address`::
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The address used for all remote connections.
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`cluster.remote.<cluster_alias>.proxy_socket_connections`::
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The number of socket connections to open per remote cluster. The default is
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`18`.
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[role="xpack"]
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`cluster.remote.<cluster_alias>.server_name`::
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An optional hostname string which is sent in the `server_name` field of
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the TLS Server Name Indication extension if
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<<encrypt-internode-communication,TLS is enabled>>. The TLS transport will fail to open
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remote connections if this field is not a valid hostname as defined by the
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TLS SNI specification.
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