Kephas.Messaging.Distributed 11.1.0-dev.3

Distributed messaging

The [[message processing|Architecture-of-messaging]] is an in-process feature, which is not per se bad, but in distributed scenarios it is limiting. The distributed messaging fills the gap by providing infrastructure components that can communicate in a such an environment.

Using the messaging infrastructure is a little more elaborate:

    // ensure the message has been sent
    await messageBroker.DispatchAsync(new RefreshCacheEvent { Key = "Users" }, ctx => ctx.OneWay()).PreserveThreadContext();   

This can be achieved in a simpler way, using the provided extension methods:

    // ensure the message has been sent
    await messageBroker.PublishAsync(new RefreshCacheEvent { Key = "Users" }).PreserveThreadContext();   

The distributed messaging flow

The participants in the distributed message flow are:

• The brokered message: This is the message being sent through the underlying infrastructure to the processors.
• The message broker: This is the in-process component dispatching the messages by the means of the underlying infrastructure.
• The brokered message handler: This is the [[message handler|Architecture-of-messaging#message-handlers]] on the other end, receiving the brokered message and ensuring that it is processed and, if requested, a proper response is sent back.
• Infrastructure dependent components which:
  • send/queue messages.
  • read the messages and forward them to the in-process [[message processor|Architecture-of-messaging#the-message-processor]] .

Brokered message

A brokered message (IBrokeredMessage) is a specialization of a [[message|Architecture-of-messaging#messages]] carrying with it the original message to be processed and some distributed environment information. It can be regarded as an "envelope" transporting the actual message.

• Content: the message to be actually processed.
• Sender: contains information about the message sender. For some broadcasts, it can be used to not forward the message to the original sender.
• Channel: contains the channel to use. If not provided, the default channel will be used.
• IsOneWay: indicates whether the sender awaits an answer to the message, or is just a fire and forget scenario.
• Timeout: the timeout for requests awaiting for a response.

The message broker

This is a [[singleton application service|Application-Services#shared-scope-shared-or-instance-based-services]] dispatching messages through a channel to registered processors.

The IMessageBroker service contract has the following methods:

• DispatchAsync(object message, [optionsConfig: Action<IDispatchingContext>], [cancellationToken: CancellationToken]): Task<IMessage>: Dispatches the brokered message asynchronously.
  • Depending on the IsOneWay setting in the brokered message, it waits for a response or not.

InProcessMessageBroker

The in-process message broker is the Kephas implementation for a message broker dispatching the message to the in-process [[message processor|Architecture-of-messaging#the-message-processor]]. It has the [[lowest override priority|Application-Services#override-priority]].

This is the default message broker used when no custom one has been defined. It is recommended to use real-world implementations, using established message queuing infrastructure.

The brokered message handler

Brokered messages are nothing more than [[message|Architecture-of-messaging#messages]] requiring proper handling. The brokered message handler is the default implementation forwarding the contained message to the in-process [[message processor|Architecture-of-messaging#the-message-processor]].