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  "description": "Pub/Sub (Publish-Subscribe) is a messaging pattern in which producers publish messages to a named channel (topic) without knowing who consumes them, and consumers subscribe to topics they care about without knowing who produced the messages. The pattern decouples producers from consumers, enabling fan-out, replay, and asynchronous processing.\n\n\nHow it differs from queues\n\n * Queue (point-to-point). Each message is consumed by one of N workers. Used for work distribution.\n * Pub/Sub (fan-out). Ea",
  "path": "/engineering-glossary/pub-sub-messaging-pattern/",
  "publishedAt": "2026-05-12T18:40:46.000Z",
  "site": "https://sahilkapoor.com",
  "tags": [
    "Event-Driven Architecture",
    "Redis",
    "Microservices",
    "Webhook",
    "Idempotency"
  ],
  "textContent": "**Pub/Sub (Publish-Subscribe)** is a messaging pattern in which producers publish messages to a named channel (topic) without knowing who consumes them, and consumers subscribe to topics they care about without knowing who produced the messages. The pattern decouples producers from consumers, enabling fan-out, replay, and asynchronous processing.\n\n## How it differs from queues\n\n  * **Queue (point-to-point).** Each message is consumed by one of N workers. Used for work distribution.\n  * **Pub/Sub (fan-out).** Each message is delivered to every interested subscriber. Used for event broadcast and integration.\n\n\n\nMany modern brokers support both patterns through different channel types or consumer-group semantics.\n\n## Common implementations\n\n  * **Streaming brokers:** Apache Kafka, Redpanda, AWS Kinesis, Azure Event Hubs, NATS JetStream, Pulsar. Messages are durable, replayable, ordered within partitions.\n  * **Cloud-managed:** Google Pub/Sub, AWS SNS (with SQS), Azure Service Bus topics, Cloudflare Queues.\n  * **In-process / low-latency:** Redis Pub/Sub, NATS Core, ZeroMQ. Fast, often fire-and-forget.\n  * **Traditional message brokers:** RabbitMQ, ActiveMQ, IBM MQ. AMQP, STOMP, MQTT protocols.\n\n\n\n## Delivery semantics\n\n  * **At-most-once.** Messages may be lost but never duplicated.\n  * **At-least-once.** Messages are never lost but may be redelivered; consumers must be idempotent.\n  * **Exactly-once.** Each message processed once; expensive and often achieved through idempotency plus transactional offsets.\n\n\n\n🔗\n\n**Related Terms**\nEvent-Driven Architecture, Redis, Microservices, Webhook, Idempotency.",
  "title": "Pub/Sub",
  "updatedAt": "2026-05-13T19:14:40.749Z"
}