433 lines
12 KiB
Plaintext
433 lines
12 KiB
Plaintext
[[modules-cross-cluster-search]]
|
|
== Cross Cluster Search
|
|
|
|
The _cross cluster search_ feature allows any node to act as a federated client across
|
|
multiple clusters. In contrast to the <<modules-tribe,tribe node>> feature, a cross cluster search node won't
|
|
join the remote cluster, instead it connects to a remote cluster in a light fashion in order to execute
|
|
federated search requests.
|
|
|
|
Cross cluster search works by configuring a remote cluster in the cluster state and connecting only to a
|
|
limited number of nodes in the 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 so that up to 3
|
|
_gateway nodes_ are selected to be connected to as part of upcoming cross cluster search requests.
|
|
Cross cluster search requests consist of uni-directional connections from the coordinating node to the previously
|
|
selected remote nodes only. It is possible to tag which nodes should be selected through
|
|
node attributes (see <<cross-cluster-search-settings>>).
|
|
|
|
Each node in a cluster that has remote clusters configured connects to one or more _gateway nodes_ and uses
|
|
them to federate search requests to the remote cluster.
|
|
|
|
[float]
|
|
=== Configuring Cross Cluster Search
|
|
|
|
Remote clusters can be specified globally using <<cluster-update-settings,cluster settings>>
|
|
(which can be updated dynamically), or local to individual nodes using the
|
|
`elasticsearch.yml` file.
|
|
|
|
If a remote cluster is configured via `elasticsearch.yml` only the nodes with
|
|
that configuration will be able to connect to the remote cluster. In other
|
|
words, federated search requests will have to be sent specifically to those
|
|
nodes. Remote clusters set via the <<cluster-update-settings,cluster settings API>>
|
|
will be available on every node in the cluster.
|
|
|
|
[WARNING]
|
|
This feature was added as Beta in Elasticsearch `v5.3` with further improvements made in 5.4 and 5.5. It requires gateway eligible nodes to be on `v5.5` onwards.
|
|
|
|
The `elasticsearch.yml` config file for a _cross cluster search_ node just needs to list the
|
|
remote clusters that should be connected to, for instance:
|
|
|
|
[source,yaml]
|
|
--------------------------------
|
|
search:
|
|
remote:
|
|
cluster_one: <1>
|
|
seeds: 127.0.0.1:9300
|
|
cluster_two: <1>
|
|
seeds: 127.0.0.1:9301
|
|
|
|
--------------------------------
|
|
<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.
|
|
|
|
The equivalent example using the <<cluster-update-settings,cluster settings API>>
|
|
to add remote clusters to all nodes in the cluster would look like the
|
|
following:
|
|
|
|
[source,js]
|
|
--------------------------------
|
|
PUT _cluster/settings
|
|
{
|
|
"persistent": {
|
|
"search": {
|
|
"remote": {
|
|
"cluster_one": {
|
|
"seeds": [
|
|
"127.0.0.1:9300"
|
|
]
|
|
},
|
|
"cluster_two": {
|
|
"seeds": [
|
|
"127.0.0.1:9301"
|
|
]
|
|
},
|
|
"cluster_three": {
|
|
"seeds": [
|
|
"127.0.0.1:9302"
|
|
]
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
--------------------------------
|
|
// CONSOLE
|
|
// TEST[setup:host]
|
|
// TEST[s/127.0.0.1:9300/\${transport_host}/]
|
|
|
|
//////////////////////////
|
|
|
|
We want to be sure that settings have been updated,
|
|
because we'll use them later.
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"acknowledged" : true,
|
|
"persistent": {
|
|
"search": {
|
|
"remote": {
|
|
"cluster_one": {
|
|
"seeds": [
|
|
"127.0.0.1:9300"
|
|
]
|
|
},
|
|
"cluster_two": {
|
|
"seeds": [
|
|
"127.0.0.1:9301"
|
|
]
|
|
},
|
|
"cluster_three": {
|
|
"seeds": [
|
|
"127.0.0.1:9302"
|
|
]
|
|
}
|
|
}
|
|
}
|
|
},
|
|
"transient" : {}
|
|
}
|
|
--------------------------------------------------
|
|
// TESTRESPONSE[s/127.0.0.1:9300/\${transport_host}/]
|
|
|
|
//////////////////////////
|
|
|
|
|
|
A remote cluster can be deleted from the cluster settings by setting its seeds to `null`:
|
|
|
|
[source,js]
|
|
--------------------------------
|
|
PUT _cluster/settings
|
|
{
|
|
"persistent": {
|
|
"search": {
|
|
"remote": {
|
|
"cluster_three": {
|
|
"seeds": null <1>
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
--------------------------------
|
|
// CONSOLE
|
|
// TEST[continued]
|
|
<1> `cluster_three` would be removed from the cluster settings, leaving `cluster_one` and `cluster_two` intact.
|
|
|
|
//////////////////////////
|
|
|
|
We want to be sure that settings have been updated,
|
|
because we'll use them later.
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"acknowledged" : true,
|
|
"persistent" : {},
|
|
"transient" : {}
|
|
}
|
|
--------------------------------------------------
|
|
// TESTRESPONSE
|
|
|
|
//////////////////////////
|
|
|
|
[float]
|
|
=== Using cross cluster search
|
|
|
|
To search the `twitter` index on remote cluster `cluster_one` the index name
|
|
must be prefixed with the cluster alias separated by a `:` character:
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
GET /cluster_one:twitter/_search
|
|
{
|
|
"query": {
|
|
"match": {
|
|
"user": "kimchy"
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
// CONSOLE
|
|
// TEST[continued]
|
|
// TEST[setup:twitter]
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"took": 150,
|
|
"timed_out": false,
|
|
"_shards": {
|
|
"total": 1,
|
|
"successful": 1,
|
|
"failed": 0,
|
|
"skipped": 0
|
|
},
|
|
"_clusters": {
|
|
"total": 1,
|
|
"successful": 1,
|
|
"skipped": 0
|
|
},
|
|
"hits": {
|
|
"total": 1,
|
|
"max_score": 1,
|
|
"hits": [
|
|
{
|
|
"_index": "cluster_one:twitter",
|
|
"_type": "_doc",
|
|
"_id": "0",
|
|
"_score": 1,
|
|
"_source": {
|
|
"user": "kimchy",
|
|
"date": "2009-11-15T14:12:12",
|
|
"message": "trying out Elasticsearch",
|
|
"likes": 0
|
|
}
|
|
}
|
|
]
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
// TESTRESPONSE[s/"took": 150/"took": "$body.took"/]
|
|
// TESTRESPONSE[s/"max_score": 1/"max_score": "$body.hits.max_score"/]
|
|
// TESTRESPONSE[s/"_score": 1/"_score": "$body.hits.hits.0._score"/]
|
|
|
|
|
|
In contrast to the `tribe` feature cross cluster search can also search indices with the same name on different
|
|
clusters:
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
GET /cluster_one:twitter,twitter/_search
|
|
{
|
|
"query": {
|
|
"match": {
|
|
"user": "kimchy"
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
// CONSOLE
|
|
// TEST[continued]
|
|
|
|
Search results are disambiguated the same way as the indices are disambiguated in the request. Even if index names are
|
|
identical these indices will be treated as different indices when results are merged. All results retrieved from a
|
|
remote index
|
|
will be prefixed with their remote cluster name:
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"took": 150,
|
|
"timed_out": false,
|
|
"_shards": {
|
|
"total": 2,
|
|
"successful": 2,
|
|
"failed": 0,
|
|
"skipped": 0
|
|
},
|
|
"_clusters": {
|
|
"total": 2,
|
|
"successful": 2,
|
|
"skipped": 0
|
|
},
|
|
"hits": {
|
|
"total": 2,
|
|
"max_score": 1,
|
|
"hits": [
|
|
{
|
|
"_index": "cluster_one:twitter",
|
|
"_type": "_doc",
|
|
"_id": "0",
|
|
"_score": 1,
|
|
"_source": {
|
|
"user": "kimchy",
|
|
"date": "2009-11-15T14:12:12",
|
|
"message": "trying out Elasticsearch",
|
|
"likes": 0
|
|
}
|
|
},
|
|
{
|
|
"_index": "twitter",
|
|
"_type": "_doc",
|
|
"_id": "0",
|
|
"_score": 2,
|
|
"_source": {
|
|
"user": "kimchy",
|
|
"date": "2009-11-15T14:12:12",
|
|
"message": "trying out Elasticsearch",
|
|
"likes": 0
|
|
}
|
|
}
|
|
]
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
// TESTRESPONSE[s/"took": 150/"took": "$body.took"/]
|
|
// TESTRESPONSE[s/"max_score": 1/"max_score": "$body.hits.max_score"/]
|
|
// TESTRESPONSE[s/"_score": 1/"_score": "$body.hits.hits.0._score"/]
|
|
// TESTRESPONSE[s/"_score": 2/"_score": "$body.hits.hits.1._score"/]
|
|
|
|
[float]
|
|
=== Skipping disconnected clusters
|
|
|
|
By default all remote clusters that are searched via Cross Cluster Search need to be available when
|
|
the search request is executed, otherwise the whole request fails and no search results are returned
|
|
despite some of the clusters are available. Remote clusters can be made optional through the
|
|
boolean `skip_unavailable` setting, set to `false` by default.
|
|
|
|
[source,js]
|
|
--------------------------------
|
|
PUT _cluster/settings
|
|
{
|
|
"persistent": {
|
|
"search.remote.cluster_two.skip_unavailable": true <1>
|
|
}
|
|
}
|
|
--------------------------------
|
|
// CONSOLE
|
|
// TEST[continued]
|
|
<1> `cluster_two` is made optional
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
GET /cluster_one:twitter,cluster_two:twitter,twitter/_search <1>
|
|
{
|
|
"query": {
|
|
"match": {
|
|
"user": "kimchy"
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
// CONSOLE
|
|
// TEST[continued]
|
|
<1> Search against the `twitter` index in `cluster_one`, `cluster_two` and also locally
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"took": 150,
|
|
"timed_out": false,
|
|
"_shards": {
|
|
"total": 2,
|
|
"successful": 2,
|
|
"failed": 0,
|
|
"skipped": 0
|
|
},
|
|
"_clusters": { <1>
|
|
"total": 3,
|
|
"successful": 2,
|
|
"skipped": 1
|
|
},
|
|
"hits": {
|
|
"total": 2,
|
|
"max_score": 1,
|
|
"hits": [
|
|
{
|
|
"_index": "cluster_one:twitter",
|
|
"_type": "_doc",
|
|
"_id": "0",
|
|
"_score": 1,
|
|
"_source": {
|
|
"user": "kimchy",
|
|
"date": "2009-11-15T14:12:12",
|
|
"message": "trying out Elasticsearch",
|
|
"likes": 0
|
|
}
|
|
},
|
|
{
|
|
"_index": "twitter",
|
|
"_type": "_doc",
|
|
"_id": "0",
|
|
"_score": 2,
|
|
"_source": {
|
|
"user": "kimchy",
|
|
"date": "2009-11-15T14:12:12",
|
|
"message": "trying out Elasticsearch",
|
|
"likes": 0
|
|
}
|
|
}
|
|
]
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
// TESTRESPONSE[s/"took": 150/"took": "$body.took"/]
|
|
// TESTRESPONSE[s/"max_score": 1/"max_score": "$body.hits.max_score"/]
|
|
// TESTRESPONSE[s/"_score": 1/"_score": "$body.hits.hits.0._score"/]
|
|
// TESTRESPONSE[s/"_score": 2/"_score": "$body.hits.hits.1._score"/]
|
|
<1> The `clusters` section indicates that one cluster was unavailable and got skipped
|
|
|
|
|
|
[float]
|
|
[[cross-cluster-search-settings]]
|
|
=== Cross cluster search settings
|
|
|
|
`search.remote.connections_per_cluster`::
|
|
|
|
The number of nodes to connect to per remote cluster. The default is `3`.
|
|
|
|
`search.remote.initial_connect_timeout`::
|
|
|
|
The time to wait for remote connections to be established when the node starts. The default is `30s`.
|
|
|
|
`search.remote.node.attr`::
|
|
|
|
A node attribute to filter out nodes that are eligible as a gateway node in
|
|
the remote cluster. For instance a node can have a node attribute
|
|
`node.attr.gateway: true` such that only nodes with this attribute will be
|
|
connected to if `search.remote.node.attr` is set to `gateway`.
|
|
|
|
`search.remote.connect`::
|
|
|
|
By default, any node in the cluster can act as a cross-cluster client and
|
|
connect to remote clusters. The `search.remote.connect` setting can be set
|
|
to `false` (defaults to `true`) to prevent certain nodes from connecting to
|
|
remote clusters. Cross-cluster search requests must be sent to a node that
|
|
is allowed to act as a cross-cluster client.
|
|
|
|
`search.remote.${cluster_alias}.skip_unavailable`::
|
|
|
|
Per cluster boolean setting that allows to skip specific clusters when no
|
|
nodes belonging to them are available and they are searched as part of a
|
|
cross cluster search request. Default is `false`, meaning that all clusters
|
|
are mandatory by default, but they can selectively be made optional by
|
|
setting this setting to `true`.
|
|
|
|
[float]
|
|
[[retrieve-remote-clusters-info]]
|
|
=== Retrieving remote clusters info
|
|
|
|
The <<cluster-remote-info, Remote Cluster Info API>> allows to retrieve
|
|
information about the configured remote clusters, as well as the remote
|
|
nodes that the Cross Cluster Search node is connected to.
|