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Auto-follow for cross-cluster replication

Auto-follow lets you automatically replicate indexes created on the leader cluster based on matching patterns. When you create an index on the leader cluster with a name that matches a specified pattern (for example, index-01*), a corresponding follower index is automatically created on the follower cluster.

You can configure multiple replication rules for a single cluster. The patterns currently only support wildcard matching.

Prerequisites

You need to set up a cross-cluster connection between two clusters before you can enable auto-follow.

Permissions

If the Security plugin is enabled, make sure that non-admin users are mapped to the appropriate permissions so they can perform replication actions. For index and cluster-level permissions requirements, see Cross-cluster replication permissions.

Get started with auto-follow

Replication rules are a collection of patterns that you create against a single follower cluster. When you create a replication rule, it starts by automatically replicating any existing indexes that match the pattern. It will then continue to replicate any new indexes that you create that match the pattern.

Create a replication rule on the follower cluster:

curl -XPOST -k -H 'Content-Type: application/json' -u 'admin:admin' 'https://localhost:9200/_plugins/_replication/_autofollow?pretty' -d '
{
   "leader_alias" : "my-connection-alias",
   "name": "my-replication-rule",
   "pattern": "movies*",
   "use_roles":{
      "leader_cluster_role": "all_access",
      "follower_cluster_role": "all_access"
   }
}'

If the Security plugin is disabled, you can leave out the use_roles parameter. If it’s enabled, however, you need to specify the leader and follower cluster roles that OpenSearch uses to authenticate requests. This example uses all_access for simplicity, but we recommend creating a replication user on each cluster and mapping it accordingly.

To test the rule, create a matching index on the leader cluster:

curl -XPUT -k -H 'Content-Type: application/json' -u 'admin:admin' 'https://localhost:9201/movies-0001?pretty'

And confirm its replica shows up on the follower cluster:

curl -XGET -u 'admin:admin' -k 'https://localhost:9200/_cat/indices?v'

It might take several seconds for the index to appear.

health status index        uuid                     pri rep docs.count docs.deleted store.size pri.store.size
yellow open   movies-0001  kHOxYYHxRMeszLjTD9rvSQ     1   1          0            0       208b           208b

Retrieve replication rules

To retrieve a list of existing replication rules that are configured on a cluster, send the following request:

curl -XGET -u 'admin:admin' -k 'https://localhost:9200/_plugins/_replication/autofollow_stats'

{
   "num_success_start_replication": 1,
   "num_failed_start_replication": 0,
   "num_failed_leader_calls": 0,
   "failed_indices":[
      
   ],
   "autofollow_stats":[
      {
         "name":"my-replication-rule",
         "pattern":"movies*",
         "num_success_start_replication": 1,
         "num_failed_start_replication": 0,
         "num_failed_leader_calls": 0,
         "failed_indices":[
            
         ]
      }
   ]
}

Delete a replication rule

To delete a replication rule, send the following request to the follower cluster:

curl -XDELETE -k -H 'Content-Type: application/json' -u 'admin:admin' 'https://localhost:9200/_plugins/_replication/_autofollow?pretty' -d '
{
   "leader_alias" : "my-conection-alias",
   "name": "my-replication-rule"
}'

When you delete a replication rule, OpenSearch stops replicating new indexes that match the pattern, but existing indexes that the rule previously created remain read-only and continue to replicate. If you need to stop existing replication activity and open the indexes up for writes, use the stop replication API operation.

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