Lambda Timing out after calling callback

Question

I'm using two lambda functions with Javascript's 4.3 runtime. I run the first and it calls the second synchronously (sync is the intent). Problem is the second one times out (at 60sec) but it actually reaches a successful finish after only 22 seconds.

Here's the flow between the two Lambda functions:

Lamda function A I am no longer getting CloudWatch logs for but the real problem (I think) is function B which times out for no reason.

Here's some CloudWatch logs to illustrate this:

The code in Function B at the end -- which includes the "Success" log statement see in picture above -- is included below:

Originally I only had the callback(null, 'successful ...') line and not the nodejs 0.10.x way where you called succeed() off of context. In desperation I added both but the result is the same.

Anyone have an idea what's going on? Any way in which I can debug this?

In case the invocation logic between A and B makes a difference in the state that B starts in, here's the invocation:

I'm still getting the hang of Lambda + Node 4.3, myself, but setting context.callbackWaitsForEmptyEventLoop = false; may be a workaround for what you are seeing, if it's similar to what I ran into -- I had a mysql connection I wasn't disconnecting, which in turn kept the event loop non-empty. Setting the value as shown proved the problem (by "fixing" the run-until-timeout); given that evidence, I was able to solve it correctly by closing that connection, at which point I no longer needed the workaround. — Michael - sqlbot
Ok, I think that's a thread I can follow; had forgotten the functional variation of what the 4.3 callback is doing. Thanks! Note: I dropped this question to AWS and they came to say a lot people are having this issue and that for many reverting to 0.10 solves the problem. That worked for me but obviously this isn't a great solution as it means there are open connections that I'd rather be closing in a graceful/controlled manner. — ken

Unknown Unknown · Accepted Answer · 2017-01-25T21:56:42

As Michael - sqlbot said; the issue seems to be that as long as there is an open connection, because of the non empty event loop, calling the callback doesn't terminate the function. Had the same problem with a open Redis connection; solution as stated is context.callbackWaitsForEmptyEventLoop = false;

Lambda Timing out after calling callback

2 Answers