Protocol Extensions

Overview

The RabbitMQ implements a number of extensions of the AMQP 0-9-1 specification, which we document here.

Some extensions introduce new protocol methods (operations); others rely on existing extension points such as optional queue arguments.

Publishing

• Publisher Confirms (aka Publisher Acknowledgements) are a lightweight way to know when RabbitMQ has taken responsibility for messages.
• Blocked Connection Notifications allows clients to be notified when a connection is blocked and unblocked.

Consuming

• Consumer Cancellation Notifications let a consumer know if it has been cancelled by the server.
• basic.nack extends basic.reject to support rejecting multiple messages at once.
• Consumer Priorities allow you to send messages to higher priority consumers first.
• Direct reply-to allows RPC clients to receive replies to their queries without needing to declare a temporary queue.

Message Routing

• Exchange to Exchange Bindings allow messages to pass through multiple exchanges for more flexible routing.
• Alternate Exchanges route messages that were otherwise unroutable.
• Sender-selected Distribution allows a publisher to decide where messages are routed directly.

Message Lifecycle

• Per-Queue Message TTL determines how long an unconsumed message can live in a queue before it is automatically deleted.
• Per-Message TTL determines the TTL on a per-message basis.
• Queue TTL determines how long an unused queue can live before it is automatically deleted.
• Dead Letter Exchanges ensure messages get re-routed when they are rejected or expire.
• Queue Length Limit allows the maximum length of a queue to be set.
• Priority Queues support the message priority field (in a slightly different way).

Authentication and Identity

• The User-ID message property is validated by the server.
• Clients that advertise the appropriate capability may receive explicit authentication failure notifications from the broker.
• update-secret to be able to renew credentials for an active connection, when those credentials can expire.

AMQP 0-9-1 Spec Differences

Some features that were in AMQP 0-8 were deprecated in AMQP 0-9-1. We have undeprecated some of them and introduced a couple of tiny behaviour changes that improve usability of the product. Please refer to the spec differences page.

There's also an AMQP 0-9-1 Errata page which explains how various