When should I use pub/sub vs point-to-point queues?

Pub/sub: multiple services need the same event, broadcast notifications, event streaming. Point-to-point: task distribution, work queues, exactly-once processing by one consumer.

How do I handle message ordering in pub/sub?

Many pub/sub systems don't guarantee ordering. If order matters: use ordering keys, process in batches with sort, design consumers to handle out-of-order, or choose systems with ordering (Kafka).

What is "at least once" vs "exactly once" delivery?

At least once: message delivered one or more times (must handle duplicates). Exactly once: message delivered precisely once (harder, often more expensive). Most systems are at-least-once.

How do I handle failed message processing?

Acknowledge only after successful processing. Use dead-letter topics for persistent failures. Implement retry with backoff. Monitor failure rates. Build idempotent consumers where possible.

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Pub/Sub (Publish-Subscribe)

A messaging pattern where senders (publishers) send messages to topics without knowledge of receivers (subscribers), who receive messages by subscribing to topics.

In-Depth Explanation

Publish-subscribe (pub/sub) is a messaging pattern that decouples message senders from receivers. Publishers send messages to topics, and subscribers receive messages from topics they've subscribed to.

Pub/sub concepts:

Publisher: Sends messages to a topic
Subscriber: Receives messages from topics
Topic: Named channel for messages
Message: Data payload published to a topic
Subscription: Subscriber's connection to a topic

Key characteristics:

One-to-many messaging
Publishers don't know about subscribers
Subscribers don't know about publishers
Messages typically broadcast to all subscribers

Use cases:

Event notifications
Real-time updates
Logging and monitoring
Cache invalidation
Microservice events

Popular implementations:

Google Cloud Pub/Sub
Amazon SNS
Azure Event Grid
Apache Kafka
Redis Pub/Sub

Business Context

Pub/sub enables event-driven architectures where services react to events without tight coupling, improving scalability and maintainability.

How Clever Ops Uses This

We implement pub/sub patterns for Australian businesses to enable event-driven AI systems, real-time notifications, and loosely coupled architectures.

Example Use Case

"AI model publishes "document processed" events to a topic; multiple services subscribe: notification service alerts user, analytics service logs metrics, storage service archives results."

Frequently Asked Questions

Related Terms

Message Queue Streaming

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