Add ccr follow info api

docs/reference/ccr/apis/ccr-apis.asciidoc

@@ -22,6 +22,7 @@ You can use the following APIs to perform {ccr} operations.
 * <<ccr-post-resume-follow,Resume follower>>
 * <<ccr-post-unfollow,Convert follower index to a regular index>>
 * <<ccr-get-follow-stats,Get stats about follower indices>>
+* <<ccr-get-follow-info,Get info about follower indices>>
 
 [float]
 [[ccr-api-auto-follow]]
@@ -40,6 +41,7 @@ include::follow/post-pause-follow.asciidoc[]
 include::follow/post-resume-follow.asciidoc[]
 include::follow/post-unfollow.asciidoc[]
 include::follow/get-follow-stats.asciidoc[]
+include::follow/get-follow-info.asciidoc[]
 
 // auto-follow
 include::auto-follow/put-auto-follow-pattern.asciidoc[]

docs/reference/ccr/apis/follow/get-follow-info.asciidoc

@@ -0,0 +1,169 @@
+[role="xpack"]
+[testenv="platinum"]
+[[ccr-get-follow-info]]
+=== Get follower info API
+++++
+<titleabbrev>Get follower info</titleabbrev>
+++++
+
+beta[]
+
+Retrieves information about all follower indices.
+
+==== Description
+
+This API lists the parameters and the status for each follower index.
+For example, the results include follower index names, leader index names,
+replication options and whether the follower indices are active or paused.
+
+==== Request
+
+//////////////////////////
+
+[source,js]
+--------------------------------------------------
+PUT /follower_index/_ccr/follow
+{
+  "remote_cluster" : "remote_cluster",
+  "leader_index" : "leader_index"
+}
+--------------------------------------------------
+// CONSOLE
+// TESTSETUP
+// TEST[setup:remote_cluster_and_leader_index]
+
+[source,js]
+--------------------------------------------------
+POST /follower_index/_ccr/pause_follow
+--------------------------------------------------
+// CONSOLE
+// TEARDOWN
+
+//////////////////////////
+
+[source,js]
+--------------------------------------------------
+GET /<index>/_ccr/info
+--------------------------------------------------
+// CONSOLE
+// TEST[s/<index>/follower_index/]
+
+==== Path Parameters
+`index` ::
+  (string) A comma-delimited list of follower index patterns
+
+==== Results
+
+This API returns the following information:
+
+`follower_indices`::
+  (array) An array of follower index statistics
+
+The `indices` array consists of objects containing several fields:
+
+`indices[].follower_index`::
+  (string) The name of the follower index
+
+`indices[].remote_cluster`::
+  (string) The <<modules-remote-clusters,remote cluster>> that contains the
+  leader index
+
+`indices[].leader_index`::
+  (string) The name of the index in the leader cluster that is followed
+
+`indices[].status`::
+  (string) Whether index following is `active` or `paused`
+
+`indices[].parameters`::
+  (object) An object that encapsulates {ccr} parameters
+
+The `parameters` contains the following fields:
+
+`indices[].parameters.max_read_request_operation_count`::
+  (integer) The maximum number of operations to pull per read from the remote
+  cluster
+
+`indices[].parameters.max_outstanding_read_requests`::
+  (long) The maximum number of outstanding read requests from the remote cluster
+
+`indices[].parameters.max_read_request_size`::
+  (<<byte-units,byte value>>) The maximum size in bytes of per read of a batch
+  of operations pulled from the remote cluster
+
+`indices[].parameters.max_write_request_operation_count`::
+  (integer) The maximum number of operations per bulk write request executed on
+  the follower
+
+`indices[].parameters.max_write_request_size`::
+  (<<byte-units,byte value>>) The maximum total bytes of operations per bulk
+  write request executed on the follower
+
+`indices[].parameters.max_outstanding_write_requests`::
+  (integer) The maximum number of outstanding write requests on the follower
+
+`indices[].parameters.max_write_buffer_count`::
+  (integer) The maximum number of operations that can be queued for writing.
+  When this limit is reached, reads from the remote cluster are deferred until
+  the number of queued operations goes below the limit
+
+`indices[].parameters.max_write_buffer_size`::
+  (<<byte-units,byte value>>) The maximum total bytes of operations that can be
+  queued for writing. When this limit is reached, reads from the remote cluster
+  are deferred until the total bytes of queued operations goes below the limit
+
+`indices[].parameters.max_retry_delay`::
+  (<<time-units,time value>>) The maximum time to wait before retrying an
+  operation that failed exceptionally. An exponential backoff strategy is
+  employed when retrying
+
+`indices[].parameters.read_poll_timeout`::
+  (<<time-units,time value>>) The maximum time to wait for new operations on the
+  remote cluster when the follower index is synchronized with the leader index.
+  When the timeout has elapsed, the poll for operations returns to the follower
+  so that it can update some statistics, then the follower immediately attempts
+  to read from the leader again
+
+==== Authorization
+
+If the {es} {security-features} are enabled, you must have `monitor` cluster
+privileges. For more information, see
+{stack-ov}/security-privileges.html[Security privileges].
+
+==== Example
+
+This example retrieves follower info:
+
+[source,js]
+--------------------------------------------------
+GET /follower_index/_ccr/info
+--------------------------------------------------
+// CONSOLE
+
+The API returns the following results:
+
+[source,js]
+--------------------------------------------------
+{
+    "follower_indices" : [
+        {
+            "follower_index" : "follower_index",
+            "remote_cluster" : "remote_cluster",
+            "leader_index" : "leader_index",
+            "status" : "active",
+            "parameters" : {
+                "max_read_request_operation_count" : 5120,
+                "max_read_request_size" : "32mb",
+                "max_outstanding_read_requests" : 12,
+                "max_write_request_operation_count" : 5120,
+                "max_write_request_size" : "9223372036854775807b",
+                "max_outstanding_write_requests" : 9,
+                "max_write_buffer_count" : 2147483647,
+                "max_write_buffer_size" : "512mb",
+                "max_retry_delay" : "500ms",
+                "read_poll_timeout" : "1m"
+            }
+        }
+    ]
+}
+--------------------------------------------------
+// TESTRESPONSE

x-pack/plugin/ccr/qa/rest/src/test/resources/rest-api-spec/test/ccr/follow_info.yml

@@ -0,0 +1,75 @@
+---
+"Test info":
+  - do:
+      cluster.state: {}
+
+  - set: {master_node: master}
+
+  - do:
+      nodes.info: {}
+
+  - set: {nodes.$master.transport_address: local_ip}
+
+  - do:
+      cluster.put_settings:
+        body:
+          transient:
+            cluster.remote.local.seeds: $local_ip
+        flat_settings: true
+
+  - match: {transient: {cluster.remote.local.seeds: $local_ip}}
+
+  - do:
+      indices.create:
+        index: foo
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+              number_of_replicas: 0
+              soft_deletes:
+                enabled: true
+
+  - do:
+      ccr.follow:
+        index: bar
+        body:
+          remote_cluster: local
+          leader_index: foo
+  - is_true: follow_index_created
+  - is_true: follow_index_shards_acked
+  - is_true: index_following_started
+
+  - do:
+      ccr.follow_info:
+        index: bar
+  - length: {follower_indices: 1}
+  - match: {follower_indices.0.follower_index: "bar"}
+  - match: {follower_indices.0.remote_cluster: "local"}
+  - match: {follower_indices.0.leader_index: "foo"}
+  - match: {follower_indices.0.status: "active"}
+  - match: {follower_indices.0.parameters.max_read_request_operation_count: 5120}
+  - match: {follower_indices.0.parameters.max_read_request_size: "32mb"}
+  - match: {follower_indices.0.parameters.max_outstanding_read_requests: 12}
+  - match: {follower_indices.0.parameters.max_write_request_operation_count: 5120}
+  - match: {follower_indices.0.parameters.max_write_request_size: "9223372036854775807b"}
+  - match: {follower_indices.0.parameters.max_outstanding_write_requests: 9}
+  - match: {follower_indices.0.parameters.max_write_buffer_count: 2147483647,}
+  - match: {follower_indices.0.parameters.max_write_buffer_size: "512mb"}
+  - match: {follower_indices.0.parameters.max_retry_delay: "500ms"}
+  - match: {follower_indices.0.parameters.read_poll_timeout: "1m"}
+
+  - do:
+      ccr.pause_follow:
+        index: bar
+  - is_true: acknowledged
+
+  - do:
+      ccr.follow_info:
+        index: bar
+  - length: {follower_indices: 1}
+  - match: {follower_indices.0.follower_index: "bar"}
+  - match: {follower_indices.0.remote_cluster: "local"}
+  - match: {follower_indices.0.leader_index: "foo"}
+  - match: {follower_indices.0.status: "paused"}
+  - is_false: follower_indices.0.parameters

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/Ccr.java

@@ -50,6 +50,7 @@
 import org.elasticsearch.xpack.ccr.action.ShardFollowTasksExecutor;
 import org.elasticsearch.xpack.ccr.action.TransportCcrStatsAction;
 import org.elasticsearch.xpack.ccr.action.TransportDeleteAutoFollowPatternAction;
+import org.elasticsearch.xpack.ccr.action.TransportFollowInfoAction;
 import org.elasticsearch.xpack.ccr.action.TransportFollowStatsAction;
 import org.elasticsearch.xpack.ccr.action.TransportGetAutoFollowPatternAction;
 import org.elasticsearch.xpack.ccr.action.TransportPauseFollowAction;
@@ -69,6 +70,7 @@
 import org.elasticsearch.xpack.ccr.repository.CcrRestoreSourceService;
 import org.elasticsearch.xpack.ccr.rest.RestCcrStatsAction;
 import org.elasticsearch.xpack.ccr.rest.RestDeleteAutoFollowPatternAction;
+import org.elasticsearch.xpack.ccr.rest.RestFollowInfoAction;
 import org.elasticsearch.xpack.ccr.rest.RestFollowStatsAction;
 import org.elasticsearch.xpack.ccr.rest.RestGetAutoFollowPatternAction;
 import org.elasticsearch.xpack.ccr.rest.RestPauseFollowAction;
@@ -80,6 +82,7 @@
 import org.elasticsearch.xpack.core.ccr.ShardFollowNodeTaskStatus;
 import org.elasticsearch.xpack.core.ccr.action.CcrStatsAction;
 import org.elasticsearch.xpack.core.ccr.action.DeleteAutoFollowPatternAction;
+import org.elasticsearch.xpack.core.ccr.action.FollowInfoAction;
 import org.elasticsearch.xpack.core.ccr.action.FollowStatsAction;
 import org.elasticsearch.xpack.core.ccr.action.GetAutoFollowPatternAction;
 import org.elasticsearch.xpack.core.ccr.action.PauseFollowAction;
@@ -202,6 +205,7 @@ public List<PersistentTasksExecutor<?>> getPersistentTasksExecutor(ClusterServic
                 // stats action
                 new ActionHandler<>(FollowStatsAction.INSTANCE, TransportFollowStatsAction.class),
                 new ActionHandler<>(CcrStatsAction.INSTANCE, TransportCcrStatsAction.class),
+                new ActionHandler<>(FollowInfoAction.INSTANCE, TransportFollowInfoAction.class),
                 // follow actions
                 new ActionHandler<>(PutFollowAction.INSTANCE, TransportPutFollowAction.class),
                 new ActionHandler<>(ResumeFollowAction.INSTANCE, TransportResumeFollowAction.class),
@@ -225,6 +229,7 @@ public List<RestHandler> getRestHandlers(Settings settings, RestController restC
                 // stats API
                 new RestFollowStatsAction(settings, restController),
                 new RestCcrStatsAction(settings, restController),
+                new RestFollowInfoAction(settings, restController),
                 // follow APIs
                 new RestPutFollowAction(settings, restController),
                 new RestResumeFollowAction(settings, restController),