How to Use basic_nack in RabbitMQ for Message Rejection

In RabbitMQ, use basic_nack to reject one or more messages from a consumer. It lets you specify if the rejected messages should be requeued or discarded, helping manage message processing failures.

Syntax

The basic_nack method has three main parameters:

• delivery_tag: The unique ID of the message to reject.
• multiple: If true, reject all messages up to the delivery tag.
• requeue: If true, the message is put back on the queue; if false, it is discarded or dead-lettered.

python

channel.basic_nack(delivery_tag=123, multiple=False, requeue=True)

Example

This example shows a Python consumer using basic_nack to reject a message and requeue it for later processing.

python

import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.queue_declare(queue='task_queue', durable=True)

def callback(ch, method, properties, body):
    print(f"Received {body.decode()}")
    try:
        # Simulate processing failure
        raise Exception("Processing error")
    except Exception as e:
        print(f"Error: {e}, rejecting message")
        ch.basic_nack(delivery_tag=method.delivery_tag, multiple=False, requeue=True)

channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=False)

print('Waiting for messages. To exit press CTRL+C')
channel.start_consuming()

Output

Waiting for messages. To exit press CTRL+C
Received Hello
Error: Processing error, rejecting message

Common Pitfalls

• Forgetting to set auto_ack=False disables manual message rejection.
• Setting requeue=True without fixing the cause can cause infinite message redelivery.
• Using multiple=True rejects multiple messages, which may cause unexpected message loss if misused.

python

## Wrong: auto_ack=True disables nack
channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=True)

## Right: auto_ack=False enables nack
channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=False)

Quick Reference

Parameter	Description	Typical Values
delivery_tag	Unique message ID to reject	Integer from message method
multiple	Reject multiple messages up to delivery_tag	True or False
requeue	Put message back on queue if True	True or False

Key Takeaways

Use basic_nack to reject messages and control if they return to the queue.

Always set auto_ack to false to enable manual message rejection.

Be careful with requeue to avoid infinite redelivery loops.

multiple=True rejects all messages up to the given delivery tag.

basic_nack helps handle message processing failures gracefully.