RabbitMQ

RabbitMQ Architecture

RabbitMQ is a message broker implementing AMQP (Advanced Message Queuing Protocol).

Core Components

RabbitMQ Architecture:

Producer → Exchange → Binding → Queue → Consumer

┌─────────────────────────────────────────────────┐
│                RabbitMQ Broker                   │
│                                                  │
│  Producer → [Exchange] → [Queue 1] → Consumer 1 │
│              ↗     ↘     [Queue 2] → Consumer 2 │
│  Producer →   [Exchange]                    │
│              ↘     ↗     [Queue 3] → Consumer 3 │
│  Producer → [Exchange]                       │
└─────────────────────────────────────────────────┘

Key Concepts

Message Flow

1. Producer publishes message to Exchange
2. Exchange routes message based on:
   - Exchange type
   - Routing key
   - Bindings
3. Message lands in matching queue(s)
4. Consumer pulls/pushes from queue
5. Consumer acknowledges message
6. Message deleted from queue

RabbitMQ Exchange Types

Exchange Types Overview

1. Direct Exchange:
   Routing key exactly matches binding key
   Producer → Exchange (routing key: "order")
           → Queue "order-queue" (binding: "order")

2. Fanout Exchange:
   Broadcasts to ALL bound queues (ignores routing key)
   Producer → Exchange → Queue 1
                      → Queue 2
                      → Queue 3

3. Topic Exchange:
   Pattern matching on routing key
   "order.created" matches "order.*"
   "order.created" matches "*.created"

4. Headers Exchange:
   Matches message headers (not routing key)

Exchange Configuration

import pika

# Connect to RabbitMQ
connection = pika.BlockingConnection(
    pika.ConnectionParameters('localhost')
)
channel = connection.channel()

# 1. Direct Exchange
channel.exchange_declare(exchange='direct_logs', exchange_type='direct')
channel.queue_declare(queue='direct_queue')
channel.queue_bind(
    exchange='direct_logs',
    queue='direct_queue',
    routing_key='error'  # Only messages with this key
)

# 2. Fanout Exchange
channel.exchange_declare(exchange='fanout_logs', exchange_type='fanout')
channel.queue_declare(queue='fanout_queue_1')
channel.queue_declare(queue='fanout_queue_2')
channel.queue_bind(exchange='fanout_logs', queue='fanout_queue_1')
channel.queue_bind(exchange='fanout_logs', queue='fanout_queue_2')

# 3. Topic Exchange
channel.exchange_declare(exchange='topic_logs', exchange_type='topic')
channel.queue_declare(queue='topic_queue')
channel.queue_bind(
    exchange='topic_logs',
    queue='topic_queue',
    routing_key='order.*'  # Matches order.created, order.updated
)

When to Use Each

RabbitMQ Routing Keys

Routing Key Patterns

Direct Exchange:
- Exact match: "error" matches "error"
- No wildcards

Topic Exchange:
- * matches exactly one word: "order.*" matches "order.created"
- # matches zero or more words: "order.#" matches "order.created.v2"

Examples:
"order.created" → matches "order.*", "*.created", "order.created"
"user.email.updated" → matches "user.*.updated", "user.#"

Routing Example

# Topic exchange with routing patterns
channel.exchange_declare(exchange='events', exchange_type='topic')

# Bind queues with patterns
channel.queue_bind(
    exchange='events',
    queue='all-orders',
    routing_key='order.#'  # All order events
)

channel.queue_bind(
    exchange='events',
    queue='all-created',
    routing_key='*.created'  # All create events
)

channel.queue_bind(
    exchange='events',
    queue='order-created',
    routing_key='order.created'  # Exact match
)

# Publish messages
channel.basic_publish(
    exchange='events',
    routing_key='order.created',
    body='{"order_id": 123}'
)
# Matches: all-orders, all-created, order-created

channel.basic_publish(
    exchange='events',
    routing_key='order.cancelled',
    body='{"order_id": 456}'
)
# Matches: all-orders only

Best Practices

1. Use meaningful routing keys: entity.action (e.g., order.created)
2. Keep hierarchy consistent: service.entity.event
3. Use topic exchange for flexibility
4. Document routing patterns for team clarity
5. Monitor queue depths for routing issues