Google Cloud Pub/Sub is a fully managed messaging service that enables asynchronous communication between applications. Processing Pub/Sub events is a fundamental skill for Cloud Engineers implementing event-driven architectures.
Pub/Sub operates on a publisher-subscriber model. Publishers send me…Google Cloud Pub/Sub is a fully managed messaging service that enables asynchronous communication between applications. Processing Pub/Sub events is a fundamental skill for Cloud Engineers implementing event-driven architectures.
Pub/Sub operates on a publisher-subscriber model. Publishers send messages to topics, and subscribers receive messages through subscriptions attached to those topics. This decouples systems, allowing them to scale independently and handle variable workloads efficiently.
To process Pub/Sub events, you first create a topic using the Console, gcloud CLI, or client libraries. For example: gcloud pubsub topics create my-topic. Next, create a subscription: gcloud pubsub subscriptions create my-subscription --topic=my-topic.
There are two subscription types for processing messages. Pull subscriptions allow your application to request messages when ready, providing control over processing rate. Push subscriptions send messages to a specified HTTPS endpoint, ideal for serverless architectures.
Cloud Functions and Cloud Run are popular choices for processing Pub/Sub events. When configuring a Cloud Function with a Pub/Sub trigger, the function automatically executes whenever a message arrives. The message data is base64-encoded and must be decoded before processing.
For reliable message processing, implement proper acknowledgment handling. Messages must be acknowledged after successful processing; otherwise, Pub/Sub redelivers them. Set appropriate acknowledgment deadlines based on your processing time requirements.
Key considerations include setting up dead-letter topics for failed messages, configuring retry policies, and monitoring subscription backlogs using Cloud Monitoring. Message ordering can be guaranteed using ordering keys when sequence matters.
Best practices include keeping message sizes under 10MB, using batching for high-throughput scenarios, and implementing idempotent processing since messages may be delivered more than once. Additionally, consider using filtering to route specific messages to appropriate subscribers, reducing unnecessary processing overhead and optimizing resource utilization in your cloud solution.
Google Cloud Pub/Sub is a foundational messaging service that enables asynchronous communication between applications. Understanding how to process Pub/Sub events is critical for building scalable, decoupled architectures on GCP. This topic appears frequently on the Associate Cloud Engineer exam because it tests your ability to design event-driven systems and integrate various GCP services.
What is Pub/Sub?
Pub/Sub (Publisher/Subscriber) is a fully managed, real-time messaging service that allows you to send and receive messages between independent applications. Key components include:
• Topics - Named resources to which messages are sent by publishers • Subscriptions - Named resources representing the stream of messages from a single topic • Publishers - Applications that create and send messages to topics • Subscribers - Applications that receive messages from subscriptions • Messages - Data combined with attributes that publishers send to topics
How Pub/Sub Event Processing Works
Push vs Pull Subscriptions:
• Pull Subscription - Subscribers explicitly call the Pub/Sub API to retrieve messages. The subscriber controls the rate of message delivery and must acknowledge messages after processing.
• Push Subscription - Pub/Sub initiates requests to your subscriber endpoint (webhook) to deliver messages. Ideal for Cloud Functions, Cloud Run, and App Engine integrations.
Message Flow:
1. Publisher sends a message to a topic 2. Pub/Sub stores the message 3. Message is delivered to all subscriptions attached to that topic 4. Subscribers receive and process the message 5. Subscribers acknowledge the message 6. Pub/Sub removes acknowledged messages from the subscription
Common Integration Patterns
• Cloud Functions with Pub/Sub Triggers - Functions automatically execute when messages arrive on a topic • Dataflow with Pub/Sub - Stream processing pipelines that consume Pub/Sub messages • Cloud Run with Push Subscriptions - Containerized applications receiving HTTP push notifications • GKE Applications with Pull Subscriptions - Kubernetes workloads pulling messages at their own pace
Key Configuration Options
• Acknowledgment Deadline - Time allowed for a subscriber to acknowledge a message (default 10 seconds, max 600 seconds) • Message Retention - Duration messages are retained (default 7 days, max 7 days) • Dead Letter Topics - Topics where undeliverable messages are sent after maximum delivery attempts • Filtering - Subscriptions can filter messages based on attributes • Ordering - Messages can be ordered using ordering keys
Exam Tips: Answering Questions on Processing Pub/Sub Events
Tip 1: Know When to Use Push vs Pull Choose Push when you have serverless backends like Cloud Functions or Cloud Run. Choose Pull when you need more control over message processing rate or when running on GKE/Compute Engine.
Tip 2: Understand At-Least-Once Delivery Pub/Sub guarantees at-least-once delivery, meaning messages may be delivered more than once. Design your processing logic to be idempotent.
Tip 3: Remember Dead Letter Topics When questions mention handling failed message processing, dead letter topics are the solution for capturing messages that cannot be processed after multiple attempts.
Tip 4: IAM Roles Matter Know the key roles: roles/pubsub.publisher for publishing, roles/pubsub.subscriber for consuming, and roles/pubsub.admin for full management.
Tip 5: Cloud Functions Integration When a question involves automatic, event-driven processing of Pub/Sub messages with minimal infrastructure management, Cloud Functions with Pub/Sub triggers is typically the correct answer.
Tip 6: Ordering and Deduplication If questions mention message ordering requirements, remember that ordering keys must be used, and ordering is only guaranteed within messages sharing the same ordering key.
Tip 7: Scaling Considerations Pub/Sub scales automatically. For pull subscriptions, multiple subscribers can process messages in parallel from the same subscription for horizontal scaling.