How can I control acknowledgement in Cloud PubSub using Node.js

Question

Basically I have created a cloud function(written a Node.js code) which will trigger on the message of cloud pubsub topic and will load that data to Bigquery table.

A message in a topic gets deleted after reading it by cloud function. I understand that subscriber internally sends acknowledgement and result of that, message gets deleted from topic.

I want to control the acknowledgement sent to publisher. How can it be achieved, didn't find any document on this.

Answer 1

Google Cloud Functions does not allow you to control the acknowledgement of the Cloud Pub/Sub message. Upon completion of the function, the message is acknowledged for the subscription. If you want finer-grained control over acknowledgements, then you will need to use Google Cloud Pub/Sub directly. There is a Node.js client library.

Just some clarifying notes on acknowledgements: Acknowledging a message for a single subscription doesn't mean the message is deleted for the topic, only for the subscription. Other independent subscriptions will still receive the message and have to acknowledge it. This is also independent of the acknowledgement sent to the publisher. When a Google Cloud Pub/Sub message is published, the publish call is acknowledged (i.e., a response is sent to the publisher) once Google Cloud Pub/Sub has saved the message and guarantees it will be delivered to subscriptions. This is one of the main advantages of an asynchronous message delivery system: receiving the message from the publisher (and acknowledging the publish) is independent of delivering the message via a subscription (which is separately acknowledged by the subscriber).