I have an AWS Lambda application built upon an external library that contains an EventEmitter. On a certain event, I need to make a HTTP request. So I was using this code (simplified):
myEmitter.on("myEvent", async() => {
setup();
await doRequest();
finishingWork();
});
What I understand that happens is this:
My handler is called, but as soon as the doRequest function is called, a Promise is returned and the EventEmitter continues with the next handlers. When all that is done, the work of the handler can continue (finishingWork).
This works locally, because my NodeJS process keeps running and any remaining events on the eventloop are handled. The strange thing is that this doesn't seem to work on AWS Lambda. Even if context.callbackWaitsForEmptyEventLoop is set to true.
In my logging I can see my handler enters the doRequest function, but nothing after I call the library to make the HTTP call (request-promise which uses request). And the code doesn't continue when I make another request (which I would expect if callbackWaitsForEmptyEventLoop is set to false, which it isn't).
Has anyone experienced something similar and know how to perform an ansynchronous HTTP request in the handler of a NodeJS event emitter, on AWS Lambda?
If you know how to solve this, feel free to add another answer. But for now, the "solution" for us was to put the eventhandler code elsewhere in our codebase. This way, it is executed asynchronously.
We were able to do that because there is only one place where the event is emitted, but the eventhandler way would have been a cleaner solution. Unfortunately, it doesn't seem like it's possible.