Query on Cross cluster Replication metadata store

Plugins Cross-Cluster Replication
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Versions (relevant - OpenSearch/Dashboard/Server OS/Browser):
I am using 2.7.0 Opensearch, opensearch dashboards in k8s environment.

Describe the issue:
From the follower cluster’s cluster-manager logs I saw below info

{"log":{"message":"PluginService:onIndexModule index:[.replication-metadata-store/rkQsv9ZbTyqatnuGQM9WrA]"}}
{"log":{"message":"[.replication-metadata-store] creating index, cause [api], templates [], shards [1]/[1]"}}
{"log":{"message":"updating number_of_replicas to [0] for indices [.replication-metadata-store]"}}
{"log":{"message":"Cluster health status changed from [YELLOW] to [GREEN] (reason: [shards started [[.replication-metadata-store][0]]])."}}

But I can’t see .replication-metadata-store index in /_cat/indices output. But inside data pod’s indices folder I see that “rkQsv9ZbTyqatnuGQM9WrA” folder getting created for this index(attached in screenshot)

So below are my queries:

  1. What is the use of .replication-metadata-store index?
  2. On what basis .replication-metadata-store index gets created?
  3. Since the folder is present in indices folder of data pod, if we run snapshot API, will it take snapshot of this index as-well? or snapshot API uses /_cat/indices output and hence it excludes this index?
  4. Does this folder (indices/rkQsv9ZbTyqatnuGQM9WrA) gets updated on every replication rule being created/deleted/updated?
    I couldn’t find any relevant document for .replication-metadata-store index.

Relevant Logs or Screenshots:

image
image946×513 22.7 KB

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  1. What is the use of .replication-metadata-store index?

This is mainly to persist the replication related indices and autofollow rules under the cluster.

  1. On what basis .replication-metadata-store index gets created?

We create the index whenever we need to store the above information, usually, it gets created during the first replication api trigger.

  1. Since the folder is present in indices folder of data pod, if we run snapshot API, will it take snapshot of this index as-well? or snapshot API uses /_cat/indices output and hence it excludes this index?

This index will also be part of snapshot and this is marked as hidden index.

  1. Does this folder (indices/rkQsv9ZbTyqatnuGQM9WrA) gets updated on every replication rule being created/deleted/updated?

Yes, If there are any updates/ addition of replication jobs or rules, this index will see the updates and eventually corresponding data folder will reflect that.

As this is an internal detail, it is not captured as part of the API related docs, Please feel free open an issue under Issues · opensearch-project/cross-cluster-replication · GitHub, we can udpdate the documentation based on further discussion.

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