I have configured a lambda function as EventBridge rule target and I have configured a Dead Letter Queue on the EventBridge rule to capture exceptions. Now, if the lambda function fails, Event Bridge does not recognize that failure as an error. Since the EventBridge invocation to the Lambda is asynchronous, for EventBridge it is enough to reach the lambda to consider the event as successfull,but in this way I am not able to track and retry events once lambda fails. Anyone know a way to make the EventBridge to the Lamdba request synchronous or another way to be able to Retry the events if the Lambda code fails after the invocation?
3 Answers
one option is to make the SQS to be rule target and use SQS event to trigger the lambda. when failure occurs, the lambda won't flag the event done so as to keep the event in the SQS. retry will auto happen after a configured period (SQS configuration). also you can configure dead letter queue after the retention time expires
AWS has a dedicated documentation page for this, which states the following for asynchronous invocation:
Lambda retries function errors twice. If the function doesn't have enough capacity to handle all incoming requests, events might wait in the queue for hours or days to be sent to the function. You can configure a dead-letter queue on the function to capture events that weren't successfully processed. For more information, see Asynchronous invocation.
So that means that as long as your Lambda functions handler function does return an error, the AWS Lambda service should retry to run your Lambda again.
Therefore, you might not need EventBridge to retry your event.
EventBridge guarantees the delivery of the event to the lambda function but is not aware of what happens post that. It's lambda invocation vs lambda execution. Eventbridge successfully delivered the message to the lambda service, so it's a successful invocation.
For Lambda, EventBridge calls invokeAsync API. So, if this API sends a success response, EventBridge will assume the delivery was successful. Any failures within Lambda from async to sync is not visible to EventBridge. We should configure retries and create DLQs in our Lambda functions to make sure the events are not lost in case the Lambda function fails to execute. We could in fact configure the same DLQ used by the EventBridge to be used by the Lambda as well so that all eventual failures land in a single place.
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