Start function execution only after previous one has executed in Google Cloud Functions

Question

I am running a node app on Google Cloud functions. This gets triggered by a webhook on Github.

Once the webhook gets triggered, my Google Cloud Function starts its function:

Function execution started

Normally if nothing happens, the function will complete to execution: Function execution took 13 ms, finished with status code: 200.

But if the webhook gets triggered again, then my Google Cloud function will abandon the function that was running and say Function execution started.

Is there a way for me to queue my functions. Have a function finish to execution and then start the next?

Answer 1

You would need a "queue" or broker mechanism in your flow. In GCP, this can be achieved by using 2 functions and a pubsub topic (and subscription)

Function 1 (GitHub webhook listener):

This function will listen for the GitHub webhook calls and publishes a pub/sub message to a topic.

Function 2 (Event handler): This function will listen for the pub/sub subscription of that topic in "push" configuration. It is vital that in the settings of this function, the max instance parameter is set to one. This will ensure that only one instance of your function is active at once, so your events get processed one after the other, waiting for one message to complete processing before moving on to the other. Also important in this function, is to carefully consider when to acknowledge the pub/sub message to allow the broker to send the next massage.