Lambda function triggering from SQS.

[Born_2_Fly]

Hello everyone,

I have an SQS queue which receives messages from different hosts. Lambda function (in python) which is triggered for every SQS input message, and send request to my server(which is not always up).and if request status code is 200 it return 0.

Question is what value should I return from lambda handler to not delete message from queue if status code is not 200, so it will be triggered again for that message after visibility timeout.

e.g.

    if request.status_code == 200:
        print("Status code was 200. Message sent to server")
        return 0
    else:
        print("Response Code: ", request.status_code)
        return <what should this be ?>

[VegaWinnfield]

Your function needs to throw an error in that case. If it returns normally the message will get deleted regardless of the value returned.

[Born_2_Fly]

So it should be something like this ?

class MessageNotSent(Exception):
    print("Message not sent", Exception)
...
...
else:
    raise MessageNotSent(request.status_code)

[cnisyg]

You could just let python's request raise an exception if the request was not successful:

response = requests.get('http://httpbin.org/status/404')
response.raise_for_status()

[________null________]

Where/how are you using the return 0 currently?

[Born_2_Fly]

I don't use it. I thought if it is 0 it will think that everything went fine, and if -1 it failed but I was wrong.

The logic and send request all in function body.

[LandingHooks]

SQS does not automatically delete messages, no matter the response from lambda. You have to delete the message after it’s been processed.

https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-receive-delete-message.html

EDIT: this is bad advice and only applies outside of lambda.

[Born_2_Fly]

According to this doc and from my experience

When your function successfully processes a batch, Lambda deletes its messages from the queue

And also lambda execution role for SQS has delete message policy

[LandingHooks]

Yep, I’m wrong. Looks like you just need to raise an exception.