114 lines
4.2 KiB
Plaintext
114 lines
4.2 KiB
Plaintext
[[modules-cross-cluster-search]]
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== Cross cluster search
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The _cross cluster search_ feature allows any node to act as a federated client across
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multiple clusters. In contrast to the _tribe_ feature, a _cross cluster search_ node won't
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join the remote cluster, instead it connects to a remote cluster in a light fashion in order to execute
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federated search requests.
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The _cross cluster search_ feature works by configuring a remote cluster in the cluster state and connects only to a
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limited number of nodes in the remote cluster. Each remote cluster is referenced by a name and a list of seed nodes.
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Those seed nodes are used to discover other nodes eligible as so-called _gateway nodes_. Each node in a cluster that
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has remote clusters configured connects to one or more _gateway nodes_ and uses them to federate search requests to
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the remote cluster.
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Remote clusters can either be configured as part of the `elasticsearch.yml` file or be dynamically updated via
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the <<cluster settings API, cluster-update-settings>>. If a remote cluster is configured via `elasticsearch.yml` only
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the nodes with the configuration set will be connecting to the remote cluster. Remote clusters set via the
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<<cluster settings API, cluster-update-settings>> will be available on every node in the cluster.
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The `elasticsearch.yml` config file for a _cross cluster search_ node just needs to list the
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remote clusters that should be connected to, for instance:
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[source,yaml]
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--------------------------------
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search:
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remote:
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cluster_one: <1>
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seeds: 127.0.0.1:9300
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cluster_two: <1>
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seeds: 127.0.0.1:9301
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--------------------------------
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<1> `cluster_one` and `cluster_two` are arbitrary names representing the connection to each cluster. These names are subsequently used to distinguish between local and remote indices.
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[float]
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=== Using cross cluster search
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To search the `twitter` index on remote cluster `cluster_1` the index name must be prefixed with the cluster name
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separated by a `:` character:
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[source,js]
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--------------------------------------------------
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POST /cluster_one:twitter/tweet/_search
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{
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"match_all": {}
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}
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--------------------------------------------------
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In contrast to the `tribe` feature cross cluster search can also search indices with the same name on different clusters:
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[source,js]
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--------------------------------------------------
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POST /cluster_one:twitter,twitter/tweet/_search
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{
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"match_all": {}
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}
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--------------------------------------------------
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Search results are disambiguated the same way as the indices are disambiguated in the request. Even if index names are
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identical these indices will be treated as different indices when results are merged. All results retrieved from a remote index
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will be prefixed with their remote cluster name:
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[source,js]
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--------------------------------------------------
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{
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"took" : 89,
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"timed_out" : false,
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"_shards" : {
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"total" : 10,
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"successful" : 10,
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"failed" : 0
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},
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"hits" : {
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"total" : 2,
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"max_score" : 1.0,
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"hits" : [
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{
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"_index" : "cluster_one:twitter",
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"_type" : "tweet",
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"_id" : "1",
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"_score" : 1.0,
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"_source" : {
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"user" : "kimchy",
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"postDate" : "2009-11-15T14:12:12",
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"message" : "trying out Elasticsearch"
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}
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},
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{
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"_index" : "twitter",
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"_type" : "tweet",
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"_id" : "1",
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"_score" : 1.0,
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"_source" : {
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"user" : "kimchy",
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"postDate" : "2009-11-15T14:12:12",
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"message" : "trying out Elasticsearch"
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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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[float]
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=== Cross cluster search settings
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* `search.remote.connections_per_cluster` - the number of nodes to connect to per remote cluster. The default is `3`
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* `search.remote.initial_connect_timeout` - the time to wait for remote connections to be established when the node starts. The default is `30s`.
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* `search.remote.node_attribute` - a node attribute to filter out nodes that are eligible as a gateway node in the remote cluster.
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For instance a node can have a node attribute `node.attr.gateway: true` such that only nodes with this attribute
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will be connected to if `search.remote.node_attribute` is set to `gateway`
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