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Add documentation for remote cluster proxy mode
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This is related to elastic#49067.
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@Tim-Brooks
Tim-Brooks committed Feb 25, 2020
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36 changes: 27 additions & 9 deletions docs/reference/cluster/remote-info.asciidoc
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Original file line number Diff line number Diff line change
Expand Up @@ -17,29 +17,47 @@ Returns configured remote cluster information.
==== {api-description-title}

The cluster remote info API allows you to retrieve all of the configured
remote cluster information. It returns connection and endpoint information keyed
remote cluster information. It returns connection and endpoint information keyed
by the configured remote cluster alias.


[[cluster-remote-info-api-response-body]]
==== {api-response-body-title}

`seeds`::
The configured initial seed transport addresses of the remote cluster.
`mode`::
The configured connection mode for the remote cluster. Will be `sniff` or
`proxy`.

`connected`::
True if there is at least one connection to the remote cluster.

`num_nodes_connected`::
The number of connected nodes in the remote cluster.

`max_connections_per_cluster`::
The maximum number of connections maintained for the remote cluster.

`initial_connect_timeout`::
The initial connect timeout for remote cluster connections.

[[skip-unavailable]]
`skip_unavailable`::
Whether the remote cluster is skipped in case it is searched through
a {ccs} request but none of its nodes are available.

`seeds`::
The configured initial seed transport addresses of the remote cluster when
sniff mode is configured.

`num_nodes_connected`::
The number of connected nodes in the remote cluster when sniff mode is
configured.

`max_connections_per_cluster`::
The maximum number of connections maintained for the remote cluster when
sniff mode is configured.

`address`::
The configured address for remote connections when proxy mode is configured.

`num_sockets_connected`::
The number of open socket connections to the remote cluster when proxy mode
is configured.

`max_socket_connections`::
The maximum number of socket connections to the remote cluster when proxy
mode is configured.
150 changes: 115 additions & 35 deletions docs/reference/modules/remote-clusters.asciidoc
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Expand Up @@ -15,21 +15,32 @@ endif::[]

// tag::how-remote-clusters-work[]
Remote cluster connections work by configuring a remote cluster and connecting
only to a limited number of nodes in that remote cluster. Each remote cluster
is referenced by a name and a list of seed nodes. When a remote cluster is
registered, its cluster state is retrieved from one of the seed nodes and up
to three _gateway nodes_ are selected to be connected to as part of remote
cluster requests.
// end::how-remote-clusters-work[]
only to a limited number of nodes in that remote cluster. There are two
potential modes for remote cluster connections: sniff mode and proxy mode.

All the communication required between different clusters
goes through the <<modules-transport,transport layer>>. Remote cluster
connections consist of uni-directional connections from the coordinating
node to the selected remote _gateway nodes_ only.
node to the remote remote connections.
// end::how-remote-clusters-work[]

[float]
[[sniff-mode]]
=== Sniff mode

// tag::how-sniff-mode-works[]
A cluster in sniff mode is created by a name and a list of seed nodes. When a
remote cluster is registered, its cluster state is retrieved from one of the
seed nodes and up to three _gateway nodes_ are selected to be connected to as
part of remote cluster requests. This mode requires that the _gateway node_
publish addresses are exposed to the local cluster.

The sniff mode is the default connection mode.
// end::how-remote-clusters-work[]

[float]
[[gateway-nodes-selection]]
=== Gateway nodes selection
==== Gateway nodes selection

The _gateway nodes_ selection depends on the following criteria:

Expand Down Expand Up @@ -62,9 +73,26 @@ communicate with 6.7. The matrix below summarizes compatibility as described abo
(see <<remote-cluster-settings>>), though such tagged nodes still have
to satisfy the two above requirements.

[float]
[[proxy-mode]]
=== Proxy mode

// tag::how-proxy-mode-works[]
A cluster in proxy mode is created by a name and a single proxy address. When
a remote cluster is registered, a configurable number of socket connections are
opened to the proxy address. The proxy is required to route those connections to
the remote cluster. Proxy mode does not require that the remote cluster nodes
publish addresses are accessible.

The proxy mode is not the default connection mode and must be configured. Similar
to the sniff <<remote-cluster-compatibility-matrix,gateway nodes>>, the remote
connections are subject to the same version compatibility rules as
<<rolling-upgrades>>.
// end::how-remote-clusters-work[]

[float]
[[configuring-remote-clusters]]
=== Configuring remote clusters
==== Configuring remote clusters

You can configure remote clusters globally by using
<<cluster-update-settings,cluster settings>>, which you can update dynamically.
Expand All @@ -83,23 +111,32 @@ cluster:
cluster_one: <1>
seeds: 127.0.0.1:9300 <2>
transport.ping_schedule: 30s <3>
cluster_two:
seeds: 127.0.0.1:9301
transport.compress: true <4>
skip_unavailable: true <5>
cluster_two: <1>
mode: sniff <4>
seeds: 127.0.0.1:9301 <2>
transport.compress: true <5>
skip_unavailable: true <6>
cluster_three: <1>
mode: proxy <4>
proxy_address: 127.0.0.1:9302 <7>
--------------------------------
<1> `cluster_one` and `cluster_two` are arbitrary _cluster aliases_ representing
the connection to each cluster. These names are subsequently used to distinguish
between local and remote indices.
<1> `cluster_one`, `cluster_two`, and `cluster_three` are arbitrary _cluster aliases_
representing the connection to each cluster. These names are subsequently used to
distinguish between local and remote indices.
<2> The hostname and <<modules-transport,transport>> port (default: 9300) of a
seed node in the remote cluster.
<3> A keep-alive ping is configured for `cluster_one`.
<4> Compression is explicitly enabled for requests to `cluster_two`.
<5> Disconnected remote clusters are optional for `cluster_two`.
<4> The configured connection mode. By default it is `sniff`, so the mode is implicit
for `cluster_one`. However, it can be explicitly configured as demonstrated by
`cluster_two` and must be explicitly configured for `proxy` mode as demonstrated by
`cluster_three`.
<5> Compression is explicitly enabled for requests to `cluster_two`.
<6> Disconnected remote clusters are optional for `cluster_two`.
<7> The address for the proxy endpoint used to connect to `cluster_three`.

For more information about the optional transport settings, see
<<modules-transport>>.
<<modules-transport>>.


If you use <<cluster-update-settings,cluster settings>>, the remote clusters
Expand All @@ -119,16 +156,16 @@ PUT _cluster/settings
"transport.ping_schedule": "30s"
},
"cluster_two": {
"mode": "sniff",
"seeds": [
"127.0.0.1:9301"
],
"transport.compress": true,
"skip_unavailable": true
},
"cluster_three": {
"seeds": [
"127.0.0.1:9302"
]
"mode": "proxy",
"proxy_address": "127.0.0.1:9302"
}
}
}
Expand All @@ -139,7 +176,8 @@ PUT _cluster/settings
// TEST[s/127.0.0.1:9300/\${transport_host}/]

You can dynamically update the compression and ping schedule settings. However,
you must re-include seeds in the settings update request. For example:
you must re-include seeds or proxy_address in the settings update request.
For example:

[source,console]
--------------------------------
Expand All @@ -155,10 +193,16 @@ PUT _cluster/settings
"transport.ping_schedule": "60s"
},
"cluster_two": {
"mode": "sniff",
"seeds": [
"127.0.0.1:9301"
],
"transport.compress": false
},
"cluster_three": {
"mode": "proxy",
"proxy_address": "127.0.0.1:9302",
"transport.compress": true
}
}
}
Expand All @@ -171,7 +215,7 @@ NOTE: When the compression or ping schedule settings change, all the existing
node connections must close and re-open, which can cause in-flight requests to
fail.

A remote cluster can be deleted from the cluster settings by setting its seeds and optional settings to `null` :
A remote cluster can be deleted from the cluster settings by setting its settings to `null` :

[source,console]
--------------------------------
Expand All @@ -181,6 +225,7 @@ PUT _cluster/settings
"cluster": {
"remote": {
"cluster_two": { <1>
"mode": null,
"seeds": null,
"skip_unavailable": null,
"transport": {
Expand All @@ -201,23 +246,15 @@ PUT _cluster/settings
[[remote-cluster-settings]]
=== Remote cluster settings

`cluster.remote.connections_per_cluster`::

The number of gateway nodes to connect to per remote cluster. The default is
`3`.
`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`.

`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`.

`cluster.remote.connect`::

By default, any node in the cluster can act as a cross-cluster client and
Expand Down Expand Up @@ -251,6 +288,49 @@ PUT _cluster/settings
Elasticsearch compresses the response. If unset, the global
`transport.compress` is used as the fallback setting.

[float]
[[remote-cluster-sniff-settings]]
=== Remote cluster sniff mode 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`::

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`.

[float]
[[remote-cluster-proxy-settings]]
=== Remote cluster proxy mode 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`.
ifndef::include-xpack[]

`cluster.remote.${cluster_alias}.server_name`::

An optional hostname string which will be sent in the server_name field of
the TLS Server Name Indication extension if
<<configuring-tls,{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.
endif::[]

[float]
[[retrieve-remote-clusters-info]]
=== Retrieving remote clusters info
Expand Down

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