Pub/Sub Architecture: Push vs Pull Messaging

Pub/Sub decouples producers from consumers, but the delivery mechanism matters enormously. Push-based systems (RabbitMQ, WebSockets) deliver messages immediately to subscribers — offering low latency but risking overwhelming slow consumers. If a subscriber can't keep up, messages back up or get dropped.

Pull-based systems (SQS, Kafka) let subscribers fetch messages at their own pace — providing natural backpressure handling and letting consumers scale independently. The trade-off is slightly higher latency since consumers poll on intervals. Hybrid approaches exist — Kafka supports both consumer group pulling and connector pushing.

Real-world example: an e-commerce order system uses push for real-time inventory alerts (speed matters) but pull for email notifications (can handle delay). Choose push when latency is critical and consumers are reliable; choose pull when throughput varies and reliability trumps speed.