331 lines
12 KiB
Plaintext
331 lines
12 KiB
Plaintext
[[modules-remote-clusters]]
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== Remote clusters
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The _remote clusters_ functionality enables you to establish unidirectional
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connections to a remote cluster. Remote clusters are required for
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<<xpack-ccr,{ccr}>> and <<modules-cross-cluster-search,{ccs}>>.
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Remote cluster connections work by configuring a remote cluster and connecting
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to a limited number of nodes in that remote cluster. There are two modes for
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remote cluster connections: <<sniff-mode,sniff mode>> and
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<<proxy-mode,proxy mode>>.
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All the communication required between different clusters
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goes through the <<modules-transport,transport layer>>. Remote cluster
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connections consist of uni-directional connections from the coordinating
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node to the remote remote connections.
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[discrete]
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[[sniff-mode]]
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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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[discrete]
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[[gateway-nodes-selection]]
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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. This is subject to rules that are similar to those for
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<<rolling-upgrades>>. Any node can communicate with any other node on the same
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major version (e.g. 7.0 can talk to any 7.x node). Only nodes on the last minor
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version of a certain major version can communicate with nodes on the following
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major version. Note that in the 6.x series, 6.8 can communicate with any 7.x
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node, while 6.7 can only communicate with 7.0. 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 matrix below summarizes compatibility as described above.
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// tag::remote-cluster-compatibility-matrix[]
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[cols="^,^,^,^,^,^,^,^"]
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|====
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| Compatibility | 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 | Yes | No | No | No | No | No
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| 5.6 | Yes | Yes | Yes | Yes | Yes | No | No
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| 6.0->6.6 | No | Yes | Yes | Yes | Yes | No | No
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| 6.7 | No | Yes | Yes | Yes | Yes | Yes | No
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| 6.8 | No | Yes | Yes | Yes | Yes | Yes | Yes
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| 7.0 | No | No | No | Yes | Yes | Yes | Yes
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| 7.1->7.x | No | No | No | No | Yes | Yes | Yes
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|====
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// end::remote-cluster-compatibility-matrix[]
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- *role*: Dedicated master nodes never get selected.
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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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[discrete]
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[[proxy-mode]]
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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. When
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a remote cluster is registered, a configurable number of socket connections are
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opened to the proxy address. The proxy is required to route those connections to
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the remote cluster. Proxy mode does not require remote cluster nodes to have
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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 globally by using
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<<cluster-update-settings,cluster settings>>, which you can update dynamically.
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Alternatively, you can configure them locally on individual nodes by using the
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`elasticsearch.yml` file.
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If you specify the settings in `elasticsearch.yml` files, only the nodes with
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those settings can connect to the remote cluster. In other words, functionality
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that relies on remote cluster requests must be driven specifically from those
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nodes. 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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transport.ping_schedule: 30s <3>
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cluster_two: <1>
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mode: sniff <4>
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seeds: 127.0.0.1:9301 <2>
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transport.compress: true <5>
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skip_unavailable: true <6>
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cluster_three: <1>
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mode: proxy <4>
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proxy_address: 127.0.0.1:9302 <7>
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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 <<modules-transport,transport>> port (default: 9300) of a
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seed node in the remote cluster.
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<3> A keep-alive ping is configured for `cluster_one`.
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<4> 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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<5> Compression is explicitly enabled for requests to `cluster_two`.
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<6> Disconnected remote clusters are optional for `cluster_two`.
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<7> The address for the proxy endpoint used to connect to `cluster_three`.
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For more information about the optional transport settings, see
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<<modules-transport>>.
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If you use <<cluster-update-settings,cluster settings>>, the remote clusters
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are available 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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"transport.ping_schedule": "30s"
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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 re-include 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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"transport.ping_schedule": "60s"
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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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}
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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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A remote cluster can be deleted from the cluster settings by setting its settings to `null` :
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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": {
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"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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--------------------------------
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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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[[remote-cluster-settings]]
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=== Remote cluster settings for all modes
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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 below.
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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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`node.remote_cluster_client`::
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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. The `node.remote_cluster_client` setting can be
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set to `false` (defaults to `true`) to prevent certain nodes from connecting
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to remote clusters. Remote cluster requests must be sent to a node that is
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allowed to act as a cross-cluster client.
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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 ensure that transport connections to nodes belonging to remote
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clusters are kept alive. If set to `-1`, application-level ping messages to
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this remote cluster are not sent. If unset, application-level ping messages
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are sent according to the global `transport.ping_schedule` setting, which
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defaults to `-1` meaning that pings are not sent.
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`cluster.remote.<cluster_alias>.transport.compress`::
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Per cluster boolean setting that enables you to configure compression for
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requests 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. If unset, the global
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`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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=== Remote cluster settings for sniff mode
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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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=== Remote cluster settings for proxy mode
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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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<<configuring-tls,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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[discrete]
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[[retrieve-remote-clusters-info]]
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=== Retrieving remote clusters info
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You can use the <<cluster-remote-info, remote cluster info API>> to retrieve
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information about the configured remote clusters, as well as the remote nodes
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that the node is connected to.
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