Fix OpenSearch Serverless Collection Tagging Without Replacement

[wadabee]

Problem

When adding cost management tags to OpenSearch Serverless Collection, CloudFormation fails with the error:

CloudFormation cannot update a stack when a custom-named resource requires replacing. Rename 3hf17j1yj99d59m78e0k and update the stack again.

This occurs because CloudFormation attempts to replace the existing resource when adding tags directly to the CfnCollection construct.

Solution

This PR implements a solution that adds tags to OpenSearch Serverless Collection using a separate Custom Resource instead of directly adding tags to the collection definition. This approach avoids the CloudFormation replacement error by:

1. Creating the collection without tags in the CloudFormation template
2. Using a dedicated Custom Resource to apply tags via AWS SDK after the collection is created
3. Ensuring proper dependency chain so tags are applied after collection creation

Implementation Details

• Added a new apply-tags.js custom resource handler that uses the AWS SDK to apply tags
• Modified the RagKnowledgeBaseStack to create collections without tags and use the custom resource for tagging
• Added appropriate IAM permissions for the tag application Lambda function

Benefits

• Allows adding cost management tags without replacing existing collections
• Preserves all existing OpenSearch indexes and data
• No service disruption during tag updates

Impact on Existing Data

• This implementation has no impact on existing OpenSearch indexes or documents
• Tagging happens at the collection metadata level only
• No index recreation or data modification occurs

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Open in Web UI: https://d2l9xhci5nmbbp.cloudfront.net/sessions/1751969257116919