Google Cloud · Professional
Google Cloud Certified - Professional Data Engineer
The forwarder to the dead-letter topic is service-<number>@gcp-sa-pubsub.iam.gserviceaccount.com, and it needs publisher on the dead-letter topic and subscriber on the source subscription. Without those roles the policy is configured but messages never move. The module grants both.
In Pub/Sub a topic doesn't store messages by itself: they're retained per subscription. If the dead-letter topic has no subscription created before messages arrive, they're lost. The minimum delivery attempts before forwarding is 5 (maximum 100).
Pub/Sub considers the message processed when the endpoint responds with 102, 200, 201, 202 or 204; any other code is a nack and Pub/Sub resends the message. The same happens if the worker takes longer than the ack deadline: Pub/Sub redelivers it while it's still running.
Pub/Sub supports exactly-once delivery only with pull subscriptions: push (what triggers Cloud Run) doesn't support it, because the client doesn't know whether Pub/Sub received the response and processed it.
Letra Chica