Is it possible for a single message to be given to multiply instance of the same subscription in gcloud PubSub

Question

I have a publisher that publishes messages to a particular topic (myTopic), then on my PubSub I create a subscription name: myTopicSub to this topic (myTopic), then I have a VM that runs a service that listeners on my subscription myTopicSub

THIS WORKS

MY PROBLEM IS: if there be a need to scale, and I add 5 more VM to handle more messages from my subscription... is it possible for PubSub to send the same message to more than one VM...

Because I only need one VM to process the message once. Please I need help

Answer 1

Cloud Pub/Sub offers at-least-once delivery. That means that a message can be delivered multiple times and in some cases, can be delivered to two different subscribers for the same subscription within a short period of time. That particular type of duplicate delivery is rare, but not impossible.

Subscribers have to be able to handle the delivery of duplicates and depending on their nature may handle it in different ways. For some, all actions are idempotent, so re-processing the same message has no ill effects. In other cases, the subscribers need to track which messages they have received and processed and if a message is a duplicate, just immediately ack the message instead of process it.