When an AMQP client establishes a connection to an AMQP server, it specifies a virtual host within which it intends to operate. A first level of access control is enforced at this point, with the server checking whether the user has any permissions to access the virtual hosts, and rejecting the connection attempt otherwise.
Resources, i.e. exchanges and queues, are named entities inside a particular virtual host; the same name denotes a different resource in each virtual host. A second level of access control is enforced when certain operations are performed on resources.
RabbitMQ distinguishes between configure, write and read operations on a resource. The configure operations create or destroy resources, or alter their behaviour. The write operations inject messages into a resource. And the read operations retrieve messages from a resource.
In order to perform an operation on a resource the user must have been granted the appropriate permissions for it. The following table shows what permissions on what type of resource are required for all the AMQP commands which perform permission checks.
|exchange.declare||(with AE)||exchange||exchange (AE)||exchange|
|queue.declare||(with DLX)||queue||exchange (DLX)||queue|
|exchange.bind||exchange (destination)||exchange (source)|
|exchange.unbind||exchange (destination)||exchange (source)|
Permissions are expressed as a triple of regular expressions - one each for configure, write and read - on per-vhost basis. The user is granted the respective permission for operations on all resources with names matching the regular expressions. (Note: For convenience RabbitMQ maps AMQP's default exchange's blank name to 'amq.default' when performing permission checks.)
The regular expression '^$', i.e. matching nothing but the empty string, covers all resources and effectively stops the user from performing any operation. Standard AMQP resource names are prefixed with amq. and server generated names are prefixed with amq.gen. For example, '^(amq\.gen.*|amq\.default)$' gives a user access to server-generated names and the default exchange. The empty string, '' is a synonym for '^$' and restricts permissions in the exact same way.
RabbitMQ may cache the results of access control checks on a per-connection or per-channel basis. Hence changes to user permissions may only take effect when the user reconnects.
When the server first starts running, and detects that its database is uninitialised or has been deleted, it initialises a fresh database with the following resources: