Description

This PR implements support for exclusion patterns in ISM template index patterns using the - prefix, similar to OpenSearch's native index pattern matching. This allows users to define broad inclusion patterns while excluding specific indices from automatic ISM policy management.

Key Changes:

• Pattern Matching Logic: Added matchesIndexPatterns() function in ManagedIndexCoordinator that separates inclusion and exclusion patterns, ensuring indices are only managed if they match an inclusion pattern and don't match any exclusion pattern
• Validation: Updated validateFormat() in ISMTemplateService to accept and validate exclusion patterns (patterns prefixed with -)
• Pattern Processing: Modified findMatchingPolicy() to use the new exclusion-aware matching logic

Example Usage:

{
  "ism_template": {
    "index_patterns": ["logs-*", "-logs-test-*", "-logs-*-debug"],
    "priority": 100
  }
}

This configuration will:

• ✅ Manage: logs-production-001, logs-staging-001
• ❌ Exclude: logs-test-001, logs-production-debug

Benefits:

• Simplifies index management by allowing users to exclude specific patterns without complex naming schemes
• Maintains backward compatibility - existing templates without exclusion patterns continue to work unchanged
• Follows OpenSearch's existing pattern matching conventions (e.g., GET /logs-*,-logs-test-*/_search)

Testing Demonstration

Step 1: Create Policy with Exclusion Patterns

Created an ISM policy with mixed inclusion and exclusion patterns:

{
  "policy": {
    "description": "testing exclude change",
    "default_state": "noop",
    "states": [
      {
        "name": "noop",
        "actions": [],
        "transitions": []
      }
    ],
    "ism_template": {
      "index_patterns": ["test-1*", "-test-12*", "test-3*", "-test-34*"], 
      "priority": 100
    }
  }
}

Step 2: Create Test Indices

Created four test indices to verify the exclusion behavior:

• test-10 - Should be managed (matches test-1*, not excluded)
• test-12 - Should NOT be managed (matches exclusion -test-12*)
• test-30 - Should be managed (matches test-3*, not excluded)
• test-34 - Should NOT be managed (matches exclusion -test-34*)

Step 3: Verify with ISM Explain API

After coordinator processing, the ISM Explain API confirms the expected behavior:

Related Issues

Resolves #375

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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