Requeue received SQS message through lambda

Question

What works: Using the AWS-SQS SDK for .Net, I'm able to receive a message batch and delete individual messages within the message visibility timer window. I can also not do anything and effectively requeue the message which then gets dead lettered if it's requeued a configured number of times.

What doesn't work: I'm trying to do the same thing using a Lambda. I've created a trigger which works meaning SQS triggers the lambda sending it a batch of messages. These messages seem to get deleted from the queue automatically when this happens. I've no control over deleting an individual message or requeuing it.

Throwing an exception in the lambda seems to get all the messages in the batch to remain in the queue. Is there a more elegant way to do this and also is there a way to do it for individual messages instead of the entire batch?

Answer 1

When you use the SQS Lambda Trigger your messages will be automatically deleted from the Queue in case of successful processing.

If you want to, you can poll messages from SQS instead of having the messages trigger your Lambda. In order to do it, just don't configure a trigger for your Lambda function and have it execute every X amount of time via a Cloud Watch Event. Upon every execution, you then poll your SQS queue for new messages. I really don't see why you'd do it though, since having the trigger and auto deletion of messages is very handy. If you want to send failed messages to a DLQ, simply set the DLQ on your source SQS queue itself. You can then customise maxReceiveCount and, once this threshold is reached, messages will then go to the configured DLQ.

From the docs:

If a message fails processing multiple times, Amazon SQS can send it to a dead letter queue. Configure a dead letter queue on your source queue to retain messages that failed processing for troubleshooting. Set the maxReceiveCount on the queue's redrive policy to at least 5 to avoid sending messages to the dead letter queue due to throttling.