Thread by @astuyve

Which would you expect would be faster, SNS directly invoking a Lambda function? Or SNS to SQS to a Lambda function?

Here's a fun thread documenting what I've learned!
🧵👇
#Serverless

In a totally unscientific test (N=3), I’ve observed SNS messages delivered directly to Lambda functions are slower than an SNS message sent to SQS, then delivered to Lambda.

Check out the following trace:

Here, the SNS message is published from the initial lambda function (purple spans). You then see the fan-out, with the yellow span indicating the time for SNS to invoke my function, and the two blue spans representing the time for SNS to SQS and then invoking my function.

The consuming functions are identical clones, and the init duration was within ~10ms for both functions, but the start times of both functions are separated by 75ms (average over 3 tests).
In this case, it’s about a 40ms difference.

@dougmoscrop helpfully pointed out that this could be explained by the fact that SNS triggers Lambda functions using an (asynchronous) Event invocation method, whereas SQS utilizes the Request/Response (synchronous) method.

This seems plausible!

Either way, it was a fun tidbit to learn, and it didn't quite fit the format of a blog post - so I hope you enjoyed this instead!