ISM policy intermittently not attaching to newly created indices in OpenSearch

Versions (relevant - OpenSearch/Dashboard/Server OS/Browser):

OpenSearch version: 2.19.0

OpenSearch Dashboard version: 2.17.0

Describe the issue:

We have defined an ISM policy and configured it through index templates.

We observed that for a few indices, the ISM policy is not getting attached, even though:

  • The ISM policy existed before index creation

  • The index template correctly references the policy

  • Most indices get the policy attached successfully

However, a small number of indices are created without any ISM policy attached.

This behavior appears to be random and inconsistent. Same ISM policy, same index pattern, same source of index creation but no identifiable pattern based on time or index name. These indices remain unmanaged unless the policy is manually attached later.

We suspect this could be related to a race condition or a bug in ISM’s background policy attachment mechanism.

Questions:

  • Is this a known issue in OpenSearch ISM?

  • Are there known race conditions or scheduler limitations that could cause this?

  • Are there recommended safeguards or workarounds?

Configuration:

One of the use cases is here:

opensearch-configs:
  ismPolicies:
    - name: proxy-sftp-access-ism-policy
      description: sftp proxy access index management policy
      defaultState: init
      ismTemplate:
        indexPatterns:
          - proxy-sftp_access*
        priority: 100
      states:
        - name: init
          actions: []
          transitions:
            - stateName: delete
              conditions:
                minIndexAge: 120d
        - name: delete
          actions:
            - delete: {}

Relevant Logs or Screenshots: