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.)
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.