GCP Pub/Sub Cheat Sheet

Topics, subscriptions, gcloud commands, and client library snippets for asynchronous messaging on Google Cloud Pub/Sub.

2 PagesIntermediateFeb 27, 2026

Create Topic & Subscription

Provision a topic and a pull subscription with gcloud.

bash

gcloud pubsub topics create orders-topicgcloud pubsub subscriptions create orders-sub \  --topic=orders-topic \  --ack-deadline=30 \  --message-retention-duration=7d# Push subscription instead of pullgcloud pubsub subscriptions create orders-push-sub \  --topic=orders-topic \  --push-endpoint=https://api.example.com/pubsub/push

Publish a Message (Python)

Publish JSON data with attributes using the google-cloud-pubsub client.

python

from google.cloud import pubsub_v1import jsonpublisher = pubsub_v1.PublisherClient()topic_path = publisher.topic_path("my-project", "orders-topic")data = json.dumps({"orderId": "o-123"}).encode("utf-8")future = publisher.publish(topic_path, data, priority="high")print(future.result())  # message ID

Pull & Ack Messages (Python)

Synchronously pull messages and acknowledge them after processing.

python

from google.cloud import pubsub_v1subscriber = pubsub_v1.SubscriberClient()sub_path = subscriber.subscription_path("my-project", "orders-sub")def callback(message):    print(message.data.decode("utf-8"))    message.ack()future = subscriber.subscribe(sub_path, callback=callback)try:    future.result(timeout=60)except TimeoutError:    future.cancel()

Core Concepts

Key Pub/Sub terms and delivery guarantees.

Topic- named resource publishers send messages to
Subscription- pull or push delivery channel attached to a topic
Ack deadline- window to acknowledge before Pub/Sub redelivers (default 10s)
At-least-once delivery- consumers must be idempotent; duplicates are possible
Dead-letter topic- routes messages after max delivery attempts are exceeded
Ordering keys- guarantee per-key ordering when enabled on the subscription

Pro Tip

Set `message-retention-duration` and enable `--enable-message-ordering` only on subscriptions that need replay or per-key ordering — both features add latency and cost that most fire-and-forget event flows don't need.

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