RabbitMQ

Also Known As

TL;DR

Explanation

RabbitMQ's model: Producer → Exchange → Queue → Consumer. Exchanges route messages: direct (exact routing key), fanout (all bound queues), topic (wildcard routing keys), headers. Message durability: declare the queue as durable and messages as persistent to survive broker restarts. Acknowledgements: the consumer calls basic_ack after processing; unacked messages redeliver on consumer disconnect. Prefetch count controls how many unacked messages a consumer holds — prevents slow consumers from starving others.

Diagram

flowchart LR
    PUB[Publisher] --> EX{Exchange}
    subgraph Routing Types
        EX -->|direct: routing key match| Q1[Queue: orders]
        EX -->|fanout: all queues| Q2[Queue: logs]
        EX -->|fanout: all queues| Q3[Queue: analytics]
        EX -->|topic: pattern match| Q4[Queue: payments.uk.*]
    end
    Q1 --> C1[Consumer 1]
    Q2 --> C2[Consumer 2]
    Q3 --> C3[Consumer 3]
    Q4 --> C4[Consumer 4]
style EX fill:#6e40c9,color:#fff
style Q1 fill:#238636,color:#fff
style Q2 fill:#1f6feb,color:#fff
style Q3 fill:#1f6feb,color:#fff
style Q4 fill:#d29922,color:#fff

Common Misconception

Why It Matters

Common Mistakes

• Not setting prefetch_count — one slow consumer takes all messages from the queue, starving other consumers.
• Declaring queue as durable but not marking messages as persistent — messages lost on broker restart.
• Not handling connection failures — AMQP connections drop; implement reconnection logic.
• No dead letter exchange — failed messages disappear silently without a DLX configured.

Code Examples

// Messages lost on restart — durable queue, non-persistent messages:
$channel->queue_declare('orders', false, true, false, false); // durable=true
$channel->basic_publish(
    new AMQPMessage('order data'), // No delivery_mode=2 — not persistent!
    '', 'orders'
);
// Broker restart: queue survives, messages gone

// Fully durable setup:
$channel->queue_declare('orders', false, true, false, false); // durable
$channel->basic_publish(
    new AMQPMessage('order data', [
        'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT, // Persistent
    ]),
    '', 'orders'
);
$channel->basic_qos(null, 1, null); // Prefetch: 1 unacked message per consumer
$channel->basic_consume('orders', '', false, false, false, false, $callback);
// Worker acks after successful processing: $msg->ack()

References

• ↗ https://www.rabbitmq.com/docs/tutorials/tutorial-two-php

Tags

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