RabbitMQ Knowledge Base

Source: Adapted from mindrally/skills (rabbitmq-development) and RabbitMQ official documentation.

Exchange Types

Type	Routing	Use for
Direct	Exact routing key match	Point-to-point, RPC
Topic	Wildcard pattern (*.info, #)	Flexible pub/sub
Fanout	Ignore routing key, broadcast to all bound queues	Broadcast notifications
Headers	Match on message headers (not routing key)	Complex routing rules

• Default exchange (empty name): direct routing by queue name. Convenient but not recommended for production.
• Always declare exchanges explicitly; don't rely on auto-created exchanges.

Queue & Routing

• Declare queues with durable=true for persistence across broker restarts.
• Bind queues to exchanges with routing keys.
• Use x-message-ttl for message expiration.
• Use x-max-length to cap queue size (drop or dead-letter oldest).
• Prefetch count (basic_qos): limit unacknowledged messages per consumer.

Durability & Reliability

• durable=true on queue + persistent delivery mode on message = survive broker restart.
• Publisher confirms: confirm_select() → broker acknowledges message receipt.
• Consumer acknowledgments: basic_ack (success) / basic_nack (failure, requeue or dead-letter).
• Never use auto_ack=true in production (message loss on consumer crash).

Dead Letter Exchange (DLX)

• Messages are dead-lettered when: rejected (basic_nack with requeue=false), TTL expired, or queue length exceeded.
• Configure with x-dead-letter-exchange and x-dead-letter-routing-key on the source queue.
• Use DLX for retry queues, error handling, and audit trails.
• Pattern: main queue → DLX → retry queue (with TTL) → main queue.

Connection & Channel

• One connection per application; multiple channels per connection.
• Channels are lightweight; connections are expensive (TCP + AMQP handshake).
• Use connection pooling for multi-threaded applications.
• Set heartbeat interval (default 60s) to detect dead connections.

Common Patterns

• Work queue: multiple consumers, round-robin dispatch, prefetch=1 for fair dispatch.
• Pub/Sub: fanout exchange, each subscriber has own queue.
• RPC: direct exchange, correlation_id + reply_to for request/response.
• Delay/Retry: DLX + TTL queue for delayed message processing.

Guardrails

• Always use publisher confirms and consumer acknowledgments.
• Never use auto_ack=true in production.
• Always declare queues and exchanges explicitly.
• Set prefetch count to prevent consumer overload.
• Monitor queue depth and consumer lag.