Message Priority

Priority for specific messages

To be able to leverage the Priority Queue feature in RabbitMq, you first have to indicate that the queue to which you are subscribing to has the x-max-priority argument. This can be done by using the optional configuration argument on the SubscribeAsync method

subscriber.SubscribeAsync<BasicMessage>(async (message, context) =>
    // do stuff
}, cfg => cfg
    .WithQueue(q => q.WithArgument(QueueArgument.MaxPriority, 3))

In this example, the prefetch count is sets to one, since the already prefetched messages would be processed before a not prefetched message with higher priority.

Now that you have a queue that honours the priority property, you can send messages to it with priority set. This is also done with the fluent configuration builder. In fact, with the builder you get access to all BasicProperties for a message.

publisher.PublishAsync(new BasicMessage
    Prop = "I am important"
}, configuration: cfg =>
    cfg.WithProperties(p => p.Priority = 9)

Setting priority based on message type

Sometime you want more of a policy like approach, like “All messages of type X is important”. This can be achieved by implementing a custom IBasicPropertiesProvider. In the method GetProperties<TMessage>(Action<IBasicProperties> custom ) you have access to the message type and it returns the properties that will be set in all outgoing messages.