Some s3 Event notifications are missing - how to doublecheck?

I think you can consider adding AWS Event Bridge or SQS between S3 Event Notification and Lambda function as well to monitor events.

To troubleshoot missing S3 event notifications for your Lambda function, you can follow these steps:

1. Check your S3 bucket configuration:

   • Open the Amazon S3 console and navigate to your bucket.
   • Go to the "Properties" tab and review the "Event notifications" section.
   • Select your event notification and choose "Edit".
   • Verify that the "Prefix" and "Suffix" settings are correct, especially for the specific folder you're having issues with.
   • Ensure that the object key in your bucket matches the object key naming guidelines and that any special characters are URL-encoded.

2. Confirm the Lambda function configuration:

   • In the S3 console, under "Destination" for your event notification, verify that the Lambda function's ARN is correct.
   • Open the Lambda console and select your function.
   • Go to the "Configuration" tab and then "Permissions".
   • Check the resource-based policy to ensure it allows Amazon S3 to invoke the Lambda function.

3. Review the Lambda function's resource-based policy:

   • The policy should include permissions for S3 to invoke the function.
   • Make sure the policy includes the correct S3 bucket ARN and your AWS account ID.

4. Check for any existing invalid event destinations:

   • Remove any non-existing event notifications from the S3 bucket.
   • Verify that all configured event destinations are valid and currently exist.

5. Consider using the AWS Systems Manager Automation runbook:

   • The "AWSSupport-TroubleshootLambdaS3Event" runbook can help identify why S3 event notifications are failing to trigger your Lambda function.
   • This automated solution can diagnose issues and provide guidance on missing permissions or other configuration problems.

Remember that S3 event notifications are usually delivered within seconds, but can sometimes take up to a minute or longer. If you've checked all these points and are still experiencing issues, you may want to contact AWS Support for further assistance.
Sources
Troubleshoot Amazon S3 event notifications for a Lambda function | AWS re:Post
AWSSupport-TroubleshootLambdaS3Event - AWS Systems Manager Automation runbook reference
Unable to validate the following destination configuration | AWS re:Post