'What happens if a Cloud Function cannot process inputs from a Pub/Sub topic as fast as they appear?
When I create a Google Cloud Function, I am offered to set a "Trigger":
and the "Maximum number of instances":
What happens if a Pub/Sub triggered Cloud Function faces periods when it receives more messages than it can instantly process?
Concrete example: I am sending 200 strings to the Cloud Function per minute, for 5 minutes. One instance can process 10 strings in a minute, and the "Maximum number of instances" is 10, so in total, 100 strings per minute is processed. What will happen to the other half of the 200 strings, will they "wait" in the Pub/Sub topic until they are processed, or will these inputs get lost?
Solution 1:[1]
What happens if a Pub/Sub triggered Cloud Function faces periods when it receives more messages than it can instantly process?
Initially, this would result to some messages to not process (UNACK will be sent), and will be left behind. However, to be able to work around with this, you just need to enable the retry policy on the function.
Cloud Functions guarantees at-least-once execution of an event-driven function for each event emitted by an event source. However, by default, if a function invocation terminates with an error, the function will not be invoked again, and the event will be dropped. When you enable retries on an event-driven function, Cloud Functions will retry a failed function invocation until it completes successfully, or the retry window (by default, 7 days) expires.
You can enable retries by providing the --retry flag when creating the function via the gcloud command-line tool or checking the "Retry on failure" box when creating via the Cloud Console.
To update the subscription to use a retry policy, find the name of the subscription created by Cloud Functions in the Cloud Console Pub/Sub section or use the gcloud pubsub subscriptions update command with the necessary flags.
Solution 2:[2]
The messages/events just queue up in the subscription until they get processed. No need to specify retry behaviour with --retry.
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
| Solution | Source |
|---|---|
| Solution 1 | Mabel A. |
| Solution 2 |