Get status of asynchronous (InvocationType=Event) AWS lambda execution

Question

I am creating an AWS step function where one of the step, let's call it step X, starts a variable number of lambdas. Since these lambda functions are long (they take between 1 and 10 minutes each to complete), I don't want to wait for them in step X. I would be spending money just for waiting. I therefore start them with InvocationType=Event so that they all run asynchronously and in parallel.

Once step X is done starting all these lambdas, I want my step function to wait for all these asynchronous functions to complete. So, a little like described here, I would create some kind of while loop in my step function. This loop would wait until all my asynchronous invocations have completed.

So the problem is: is it possible to query for the status of an AWS lambda that was started with InvocationType=Event?

If it is not possible, I would need my lambdas to persist their status somewhere so that I can poll this status. I would like to avoid this strategy since it does not cover problems that occur outside of my lambda (ex: out of memory, throttling exceptions, etc.)

Answer 1

Since the question was initially posted, AWS added the support for dynamic parallelism in workflows. The need to manually start lambda functions and poll for their completion from within a step function is therefore now an anti-pattern.

Answer 2

instead of polling,(which again is expensive), you can provide a callback, for the lambda to post back asynchronously. once you get all positives for all lambdas, then continue the process.

Answer 3

An asynchronously invoked Lambda is a "fire and forget" use case. There's no straightforward way to get its result. I'm afraid you'll have to write your own job synchronization logic.