RabbitMQ Delayed Message Plugin

This plugin adds delayed-messaging (or scheduled-messaging) to RabbitMQ.

A user can declare an exchange with the type x-delayed-message and then publish messages with the custom header x-delay expressing in milliseconds a delay time for the message. The message will be delivered to the respective queues after x-delay milliseconds.

Installing

TODO (I assume the plugin will be offered from community-plugins).

Usage

To use the delayed-messaging feature, declare an exchange with the type x-delayed-message:

... elided code ...

Declare = #'exchange.declare' {
              exchange    = <<"my-exchange">>",
              type        = <<"x-delayed-message">>,
              durable     = true,
              auto_delete = false,
              arguments   = [{<<"x-delayed-type">>,
                              longstr, <<"direct">>}]
      },
amqp_channel:call(Chan, Declare),

... more code ...

Note that we pass an extra header called x-delayed-type, more on it under the Routing section.

Once we have the exchange declared we can publish messages providing a header telling the plugin for how long to delay our messages:

... elided code ...
amqp_channel:call(Chan,
                  #'basic.publish'{exchange = Ex},
                  #amqp_msg{props   = #'P_basic'{headers = [{<<"x-delay">>, signedint, 5000}]},
                            payload = <<"delayed payload">>}),

amqp_channel:call(Chan,
                  #'basic.publish'{exchange = Ex},
                  #amqp_msg{props   = #'P_basic'{headers = [{<<"x-delay">>, signedint, 1000}]},
                            payload = <<"more delayed payload">>}),

... more code ...

In the above example we publish two messages, specifying the delay time with the x-delay header. For this example, the plugin will deliver to our queues first the message with the body <<"more delayed payload">> and then the one with the body <<delayed payload">>.

If the x-delay header is not present, then the plugin will proceed to route the message without delay.

Routing

This plugin allows for flexible routing via the x-delayed-type arguments that can be passed during exchange.declare. In the example above we used <<"direct">> as exchange type. That means the plugin will have the same routing behavior shown by the direct exchange.

If you want a different routing behavior, then you could provide a different exchange type, like <<"topic">> for example. You can also specify exchange types provided by plugins. Note that this argument is required and must refer to an existing exchange type.

Disabling the Plugin

You can disable this plugin by calling rabbitmq-plugins disable rabbitmq_delayed_messaging but note that ALL DELAYED MESSAGES THAT HAVEN'T BEEN DELIVERED WILL BE LOST.

Plugin Status

At the moment the plugin is experimental in order to receive feedback from the community.

LICENSE

See the LICENSE file.