Fix GCP Pub/Sub Dead Letter Errors

When working with GCP Pub/Sub, you may encounter a configuration error that prevents your data pipeline or messaging system from working. This guide explains the most common mistake with dead letter and shows the exact fix.

A Common Mistake

Not configuring a dead letter topic for a subscription, causing messages that repeatedly fail to be retried indefinitely with no escalation path.

The incorrect command:

gcloud pubsub subscriptions create my-sub --topic=my-topic

Error output:

Created subscription without dead letter topic.
A message with malformed content is published:
Subscriber tries to process: fails.
Retries: 100+ times over 12 days.
Each retry consumes resources. The failing message blocks the subscription queue. No alert is triggered. Eventually the message expires from retention.

The Correct Approach

The right way to configure dead letter in GCP Pub/Sub:

gcloud pubsub subscriptions create my-sub --topic=my-topic --dead-letter-topic=my-dead-letter-topic --max-delivery-attempts=5

Successful result:

Created subscription with dead letter topic.
After 5 delivery attempts fail, the message is moved to the dead letter topic. A Cloud Function monitors the DLQ and alerts the team. A human reviews and fixes the message format, then seeks the message back to the subscription.

How to Prevent This

Always configure a dead letter topic for production subscriptions. Set max delivery attempts (5-10 recommended). Monitor the dead letter topic backlog. Set up alerts for messages in DLQ. DLQ messages expire based on the topic retention (default 7 days). Use Cloud Functions or a script to process DLQ messages.

FAQ

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