Is there a response code to mark a Google Cloud Task as permanently failed so it won't retry?

Question

I have a Firebase HTTPS function that sends timed messages and is triggered by Google Cloud Tasks.

According to the Cloud Tasks documentation, any response code outside the 200 range is seen as a failure and will trigger a retry.

This function needs to scale to millions of daily messages, so we need to avoid retrying messages that have a permanent failure (the person opted out, etc).

Note: This is especially important in this example because each task needs to look up the latest information before processing, adding 2-10 Firestore reads to each attempt. We can't send this info in the payload because it might change between the time the message was queued and it is processed.

Its easy to delete the task using the cloud task API, but I was wondering if there is any HTTP response code (or header) that can mark these tasks as permanently failed (400 bad request for example) and not to retry them.

Answer 1

Only the HTTP code 2XX (from 200 to 299) are considered as a task completion and stops the retries.

All other return code are considered as a failure and imply a retry.

Note: 429 (and 503 for App Engine task queue) throttle the retries on the queue (to prevent service congestion).

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If you want to stop the retry mechanism by Cloud Task, return a 2XX code. That's the only way.

You can imagine to return 299 and to plug Error Reporting alert on this specific code to track them and be alerted on these cases