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[DOCS] Add 'Selecting gateway and seed nodes' section to CCS docs #48297

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Oct 21, 2019
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[DOCS] Add 'Selecting gateway and seed nodes' section to CCS docs #48297

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30 changes: 25 additions & 5 deletions docs/reference/modules/cross-cluster-search.asciidoc
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Expand Up @@ -242,9 +242,31 @@ PUT _cluster/settings
If `cluster_two` is disconnected or unavailable during a {ccs}, {es} won't
include matching documents from that cluster in the final results.

[float]
[discrete]
[[ccs-works]]
== How {ccs} works

include::./remote-clusters.asciidoc[tag=how-remote-clusters-work]

[discrete]
[[ccs-gateway-seed-nodes]]
=== Selecting gateway and seed nodes

Gateway and seed nodes need to be accessible from the local cluster via your
network.

By default, any master-ineligible node can act as a gateway node. If wanted,
you can define the gateway nodes for a cluster by setting
`cluster.remote.node.attr.gateway` to `true`.

For {ccs}, we recommend you use gateway nodes that are capable of serving as
<<coordinating-node,coordinating nodes>> for search requests. If
wanted, the seed nodes for a cluster can be a subset of these gateway nodes.

[discrete]
[[ccs-network-delays]]
=== How {ccs} handles network delays

Because {ccs} involves sending requests to remote clusters, any network delays
can impact search speed. To avoid slow searches, {ccs} offers two options for
handling network delays:
Expand All @@ -268,11 +290,9 @@ latency.
+
See <<ccs-unmin-roundtrips>> to learn how this option works.



[float]
[[ccs-min-roundtrips]]
=== Minimize network roundtrips
==== Minimize network roundtrips

Here's how {ccs} works when you minimize network roundtrips.

Expand All @@ -297,7 +317,7 @@ image:images/ccs/ccs-min-roundtrip-client-response.png[]

[float]
[[ccs-unmin-roundtrips]]
=== Don't minimize network roundtrips
==== Don't minimize network roundtrips

Here's how {ccs} works when you don't minimize network roundtrips.

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6 changes: 5 additions & 1 deletion docs/reference/modules/remote-clusters.asciidoc
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Expand Up @@ -13,12 +13,16 @@ connections to a remote cluster. This functionality is used in
<<modules-cross-cluster-search,{ccs}>>.
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. All the communication required between different clusters
cluster requests.
// end::how-remote-clusters-work[]

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.
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