Direct exchange in RabbitMQ - Commands & Configuration

Introduction

A direct exchange in RabbitMQ routes messages to queues based on an exact matching routing key. It helps deliver messages precisely to the intended queue without confusion.

When you want to send a message to a specific queue identified by a unique key.

When you have multiple queues and want to control exactly which queue receives which message.

When you need simple routing without complex pattern matching.

When building a task queue where each task type has its own queue.

When you want to ensure messages do not get broadcasted to unintended queues.

Config File - direct_exchange_setup.sh

direct_exchange_setup.sh

#!/bin/bash

# Declare a direct exchange named 'my_direct_exchange'
curl -i -u guest:guest -H "content-type:application/json" \
  -XPUT \
  -d '{"type":"direct"}' \
  http://localhost:15672/api/exchanges/%2f/my_direct_exchange

# Declare a queue named 'task_queue'
curl -i -u guest:guest -H "content-type:application/json" \
  -XPUT \
  -d '{}' \
  http://localhost:15672/api/queues/%2f/task_queue

# Bind the queue to the exchange with routing key 'task_key'
curl -i -u guest:guest -H "content-type:application/json" \
  -XPOST \
  -d '{"routing_key":"task_key"}' \
  http://localhost:15672/api/bindings/%2f/e/my_direct_exchange/q/task_queue

This script creates a direct exchange called my_direct_exchange. It then creates a queue named task_queue. Finally, it binds the queue to the exchange using the routing key task_key. Messages sent to the exchange with this key will go to task_queue.

Commands

This command creates a direct exchange named 'my_direct_exchange' where messages will be routed based on exact routing keys.

Terminal

rabbitmqadmin declare exchange name=my_direct_exchange type=direct

Expected Output

Successfully declared exchange 'my_direct_exchange'

→

name - Specifies the name of the exchange to create

→

type - Sets the exchange type to direct for exact routing

This command creates a durable queue named 'task_queue' that will receive messages routed by the exchange.

Terminal

rabbitmqadmin declare queue name=task_queue durable=true

Expected Output

Successfully declared queue 'task_queue'

→

name - Specifies the queue name

→

durable - Makes the queue survive server restarts

This command binds the 'task_queue' to the 'my_direct_exchange' exchange with the routing key 'task_key'. Messages with this key go to this queue.

Terminal

rabbitmqadmin declare binding source=my_direct_exchange destination=task_queue destination_type=queue routing_key=task_key

Expected Output

Successfully declared binding from 'my_direct_exchange' to 'task_queue' with routing key 'task_key'

→

source - The exchange name

→

destination - The queue name

→

destination_type - Specifies that the destination is a queue

→

routing_key - The exact key used for routing messages

This command sends a message with the routing key 'task_key' to the direct exchange. It will be delivered to 'task_queue'.

Terminal

rabbitmqadmin publish exchange=my_direct_exchange routing_key=task_key payload='Hello Direct Exchange!'

Expected Output

Message published

→

exchange - Specifies which exchange to send the message to

→

routing_key - The routing key to match the queue binding

→

payload - The message content

This command retrieves the message from 'task_queue' to verify it was routed correctly.

Terminal

rabbitmqadmin get queue=task_queue requeue=false

Expected Output

Message count: 0

Payload: Hello Direct Exchange!

→

queue - Specifies the queue to get messages from

→

requeue - Whether to put the message back after getting it; false means remove it

Key Concept

If you remember nothing else from this pattern, remember: a direct exchange routes messages only to queues whose binding key exactly matches the message's routing key.

Common Mistakes

Using a routing key in the message that does not exactly match any queue binding key.

The message will not be delivered to any queue and will be lost or dropped.

Always ensure the routing key in the message matches exactly one of the queue binding keys.

Binding a queue to the exchange without specifying a routing key.

The binding will not work as expected because direct exchanges require routing keys for matching.

Always specify a routing key when binding a queue to a direct exchange.

Publishing messages to the wrong exchange type or name.

Messages will not be routed correctly and may be lost.

Double-check the exchange name and type before publishing messages.

Summary

Create a direct exchange to route messages by exact routing keys.

Declare queues and bind them to the exchange with specific routing keys.

Publish messages with routing keys to deliver them to the correct queue.

Retrieve messages from the queue to verify correct routing.