Dead Letter Queues (DLQ) for Failures

When building serverless applications, especially with asynchronous Lambda functions, what happens if an invocation fails repeatedly?

Without a proper mechanism, these failed events might simply be discarded, leading to data loss or unaddressed issues. This is where Dead Letter Queues (DLQs) come in.

First, let's quickly recap how asynchronous Lambda invocations work. When you invoke a Lambda function asynchronously (e.g., via S3, SNS, or direct API call with InvocationType: Event):

• Lambda places the event in an internal queue.
• It then attempts to invoke your function.
• If the function fails, Lambda automatically retries the invocation up to two times.