Reliability, Schemas & Operations

Dead-Letter Topics

gcloud pubsub topics create order-events-dlq

gcloud pubsub subscriptions create inventory-sub \
  --topic=order-events \
  --dead-letter-topic=order-events-dlq \
  --max-delivery-attempts=5

# After 5 failed processing attempts, the message moves to the DLQ
# instead of retrying forever or being silently dropped.

Schema Validation

Attaching an Avro or Protocol Buffer schema to a topic validates published messages against an agreed structure BEFORE Pub/Sub accepts them — catching a producer bug at publish time instead of letting malformed data reach every subscriber, each of which would otherwise need its own duplicated validation logic.

Backlog & Scaling

A growing backlog (watch subscription/num_undelivered_messages) means subscribers can't ack messages as fast as they're published — either scale out subscriber capacity (more pull workers, more push instances) or fix the actual bottleneck (a slow downstream call, a rate-limited external API) causing the slow ack rate.

IAM Permissions

gcloud pubsub topics add-iam-policy-binding order-events \
  --member="serviceAccount:order-service@my-project.iam.gserviceaccount.com" \
  --role="roles/pubsub.publisher"

gcloud pubsub subscriptions add-iam-policy-binding inventory-sub \
  --member="serviceAccount:inventory-service@my-project.iam.gserviceaccount.com" \
  --role="roles/pubsub.subscriber"