AWS Lambda Publishing to SNS

Question

I'm experiencing a strange issue with Amazon SNS. When I publish a message using the AWS UI (publish to topic button), messages are delivered immediately.

But when I publish a message to the same topic from inside a lambda function, messages will either not be delivered, or will be delivered after some more messages are published by future invocations of the lambda.

What could be different?

Update

I tried publishing with the AWS CLI cool, and that works fine also.

I'm using the Java SNS library for my lambda. I'm using the default credentials of the lambda. I construct the PublishRequest with just the topic ARN, message, and subject. The publish call returns successfully, and I see it my logs in the cloudwatch logs.

What would cause an SNS message to delay in being delivered until more SNS messages are sent? I'm testing out with both Email and SQS subscriptions - both behave the same.

Might not be the case, but check that your SNS call is completing before the Lambda function exits. The asynchronous stuff could cause the function to complete before all calls have finished. — John Rotenstein
Yea, I definitely wait on all my async stuff before returning. What is weird to me is that the messages will show up later only after I send more. Almost like they are buffered somewhere. This would be horrible if its true. But again, this only happens when I send in the lambda. — ademartini

ademartini ademartini · Accepted Answer · 2015-08-23T11:07:53

I figured out the problem. Although I thought I was waiting for the SNS publish request to send, I actually wasn't. So bottom line, make sure your async stuff finishes in these lambdas or you could see strange behavior. Thanks to John Rotenstein above for pointing me in the right direction.

AWS Lambda Publishing to SNS

1 Answers