This project aims to explain how RabbitMQ works internally. The goal is to make it easier to contribute for newcomers to the project, and at the same time have a common repository of knowledge to be shared across the project contributors.

Most interesting modules in RabbitMQ projects have documentation essays, sometimes quite extensive, at the top. The aim here is not to duplicate what's there, but to provide the highest-level overview as to the overall architecture.

In order to understand how RabbitMQ's internals work, it's better to try to follow the logic of how a message progresses through RabbitMQ as it is handled by the broker, otherwise, you would end up navigating through many guides without a clear context of what's going on, or without knowing what to read next. Therefore we have prepared the following guides to help you understand how RabbitMQ works:

Here we follow the life of a message since it's received from the network until it has been routed by the exchanges. We take a look at the various processing steps that happen to a message right until it is delivered to one or perhaps many queues.

Basic Publish

After the message has been routed, the broker needs to deliver that message to the respective queues. Here not only the message has to be sent to queues, but also mandatory messages and publisher confirms need to be taken into account. Also, the queue needs to try to deliver the message to prospective consumer, otherwise the message ends up queued.

Deliver To Queues

Provides an overview of the Erlang processes that back queues and how they interact with the message store, message index and so on.

Queues and Message Store

Ultimately, messages end up queued at the backing queue. From here they can be retrieved, acked, purged, and so on. The most common implementation of the backing queue behaviour is the rabbit_variable_queue module, explained in the following guide:

Variable Queue

As explained on the Deliver To Queues guide, a channel has to handle messages published as mandatory and also take care of publisher confirms. These processes are explained in the following guides:

• Mandatory Message Handling
• Publisher Confirms

As explained in the Basic Publish, there are some rules to see if a message can be accepted by the broker from a certain publisher. This is explained in the following guide:

Authorization and Authentication Backends

In some cases components in a running node communicate via events. Some events are consumed by other nodes.

Internal Events

An architectural overview of the v3.6.7+ version of the management plugin.

Metrics and Management Plugin

These guides are not complete, haven't been edited, and are work in progress in general.

So if you find yourself wanting more detail, check the code first!

(c) Pivotal Software Inc, 2015-2016

Released under the Creative Commons Attribution-ShareAlike 3.0 Unported license.