[[indices-resolve-cluster-api]]
=== Resolve cluster API
++++
<titleabbrev>Resolve cluster</titleabbrev>
++++

Resolves the specified index expressions to return information about
each cluster, including the local cluster, if included.

This endpoint is useful before doing a <<modules-cross-cluster-search,{ccs}>> in
order to determine which remote clusters should be included in a search.

You use the same index expression with this endpoint as you would for cross-cluster
search. Index and <<exclude-problematic-clusters,cluster exclusions>> are also supported
with this endpoint.

For each cluster in the index expression, information is returned about:

1. whether the querying ("local") cluster is currently connected to each remote cluster
   in the index expression scope
2. whether each remote cluster is configured with `skip_unavailable` as `true` or `false`
3. whether there are any indices, aliases or data streams on that cluster that match
   the index expression
4. whether the search is likely to have errors returned when you do the {ccs} (including any
   authorization errors if your user does not have permission to query the index)
5. cluster version information, including the Elasticsearch server version

////
[source,console]
--------------------------------
PUT _cluster/settings
{
  "persistent": {
    "cluster": {
      "remote": {
        "cluster_one": {
          "seeds": [
            "35.238.149.1:9300"
          ],
          "skip_unavailable": true
        },
        "cluster_two": {
          "seeds": [
            "35.238.149.2:9300"
          ],
          "skip_unavailable": false
        }
      }
    }
  }
}
--------------------------------
// TEST[setup:host]
// TEST[s/35.238.149.\d+:930\d+/\${transport_host}/]
////

[source,console]
----
GET /_resolve/cluster/my-index-*,cluster*:my-index-*
----
// TEST[continued]

This will return information about the local cluster and all remotely configured
clusters that start with the alias `cluster*`. Each cluster will return information
about whether it has any indices, aliases or data streams that match `my-index-*`.

[[resolve-cluster-api-request]]
==== {api-request-title}

`GET /_resolve/cluster/<index_expression>`

[[resolve-cluster-api-prereqs]]
==== {api-prereq-title}

* If the {es} {security-features} are enabled, you must have the
`view_index_metadata`, `read`, or `manage` <<privileges-list-indices,index
privilege>> for the target data stream, index, or alias.

[[resolve-cluster-api-path-params]]
==== {api-path-parms-title}

`<index_expression>`::
+
--
(Required, string) Comma-separated name(s) or index pattern(s) of the
indices, aliases, and data streams to resolve, using <<api-multi-index>>.
Resources on <<remote-clusters,remote clusters>> can be specified using the
`<cluster>:<name>` syntax.
--

[[resolve-cluster-api-query-params]]
==== {api-query-parms-title}

include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=expand-wildcards]
+
Defaults to `open`.

include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=index-ignore-unavailable]
+
Defaults to `false`.

include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=allow-no-indices]
+
Defaults to `true`.

`ignore_throttled`::
(Optional, Boolean) If `true`, concrete, expanded or aliased indices are
ignored when frozen. Defaults to `false`.
+
deprecated:[7.16.0]


[discrete]
[[usecases-for-resolve-cluster]]
=== Advantages of using this endpoint before a {ccs}

You may want to exclude a cluster or index from a search when:

1. A remote cluster is not currently connected and is configured with `skip_unavailable`=`false`.
Executing a {ccs} under those conditions will cause
<<cross-cluster-search-failures,the entire search to fail>>.

2. A cluster has no matching indices, aliases or data streams for the index expression
(or your user does not have permissions to search them). For example, suppose your
index expression is `logs*,remote1:logs*` and the `remote1` cluster has no indices, aliases or data
streams that match `logs*`. In that case, that cluster will return no results from that cluster if
you include it in a {ccs}.

3. The index expression (combined with any query parameters you specify) will likely cause an exception
to be thrown when you do the search. In these cases, the "error" field in the `_resolve/cluster` response
will be present. (This is also where security/permission errors will be shown.)

4. A remote cluster is an older version that does not support the feature you want to
use in your search.


[[resolve-cluster-api-example]]
==== {api-examples-title}

[source,console]
----
GET /_resolve/cluster/my-index*,clust*:my-index*
----
// TEST[continued]
// TEST[setup:my_index]

The API returns the following response:

[source,console-result]
----
{
  "(local)": {          <1>
    "connected": true,
    "skip_unavailable": false,
    "matching_indices": true,
    "version": {
      "number": "8.13.0",
      "build_flavor": "default",
      "minimum_wire_compatibility_version": "7.17.0",
      "minimum_index_compatibility_version": "7.0.0"
    }
  },
  "cluster_one": {
    "connected": true,         <2>
    "skip_unavailable": true,  <3>
    "matching_indices": true,  <4>
    "version": {
      "number": "8.13.0",      <5>
      "build_flavor": "default",
      "minimum_wire_compatibility_version": "7.17.0",
      "minimum_index_compatibility_version": "7.0.0"
    }
  },
  "cluster_two": {
    "connected": true,
    "skip_unavailable": false,
    "matching_indices": true,
    "version": {
      "number": "8.13.0",
      "build_flavor": "default",
      "minimum_wire_compatibility_version": "7.17.0",
      "minimum_index_compatibility_version": "7.0.0"
    }
  }
}
----
// TESTRESPONSE[s/"number": "8.13.0"/"number": "$body.$_path"/]
// TESTRESPONSE[s/"minimum_wire_compatibility_version": "7.17.0"/"minimum_wire_compatibility_version": "$body.$_path"/]
// TESTRESPONSE[s/"minimum_index_compatibility_version": "7.0.0"/"minimum_index_compatibility_version": "$body.$_path"/]

<1> Each cluster has its own response section. The cluster you sent the request to is labelled as "(local)".
<2> The querying cluster attempts to make a request to each remote cluster. If successful, `connected`=`true`.
<3> The `skip_unavailable` setting for each remote cluster, as configured on the local cluster.
<4> Indicates whether any index, alias or data stream matches the index expression specified for that cluster.
<5> The Elasticsearch server version.


[discrete]
[[resolve-cluster-api-error-example]]
==== Identifying potential problems with your {ccs}

The following request shows several examples of how modifying your query can
prevent search failures.

[source,console]
--------------------------------------------------
GET /_resolve/cluster/not-present,clust*:my-index*,oldcluster:*?ignore_unavailable=false
--------------------------------------------------
// TEST[continued]
// TEST[s/,oldcluster:*//]

[source,console-result]
--------------------------------------------------
{
  "(local)": {
    "connected": true,
    "skip_unavailable": false,
    "error": "no such index [not_present]"  <1>
  },
  "cluster_one": {
    "connected": true,
    "skip_unavailable": true,
    "matching_indices": false,    <2>
    "version": {
      "number": "8.13.0",
      "build_flavor": "default",
      "minimum_wire_compatibility_version": "7.17.0",
      "minimum_index_compatibility_version": "7.0.0"
    }
  },
  "cluster_two": {
    "connected": false,           <3>
    "skip_unavailable": false,
    "matching_indices": true,
    "version": {
      "number": "8.13.0",
      "build_flavor": "default",
      "minimum_wire_compatibility_version": "7.17.0",
      "minimum_index_compatibility_version": "7.0.0"
    }
  },
  "oldcluster": {         <4>
    "connected": true,
    "skip_unavailable": false,
    "matching_indices": true
  }
}
--------------------------------------------------
// TEST[skip: too many illustrative error variations to reproduce]

<1> The local cluster has no index called `not_present`. Searching against it
using the specified `ignore_unavailable=false` param will return a "no such
index" error. Other types of errors can show up here as well, such as security
permission errors when the user does not have authorization to search the
specified index.
<2> The `cluster_one` remote cluster has no indices that match the pattern
`my-index*`. There may be no indices that match the pattern or the index
could be closed. (You can check this by using the
<<indices-resolve-index-api,resolve index>> API.)
<3> The `cluster_two` remote cluster is not connected (the attempt to connect
failed). Since this cluster is marked as `skip_unavailable=false`, you should
probably exclude this cluster from the search by adding `-cluster_two:*` to the
search index expression.
<4> The `oldcluster` remote cluster shows that it has matching indices, but no
version information is included. This indicates that the cluster version predates
the introduction of the `_resolve/cluster` API in 8.13.0., so you may want to
exclude it from your {ccs}. (Note: the endpoint was able to tell there were
matching indices because it fell back to using the <<indices-resolve-index-api,
resolve index>> API.)
