Satellites

Satellites are lightweight message processors that run in the same process as their owning endpoint. While they are mostly used by NServiceBus to implement infrastructure features like the TimeoutManager and Gateway, they can be used in scenarios where messages from additional queues other than the main input queue need to be processed. This is useful when the robustness of a separate queue is needed without having to create and setup a new endpoint and configure any message mappings.

Satellites are extension points to handle messages that arrive in different queues other than the endpoint's main queue. This extension point is useful when the robustness of a separate queue is needed without having to create and setup a new endpoint and configure any message mappings.

These extensions are available as ISatellite and IAdvancedSatellite interfaces.

ISatellite

To use this extension, declare a class that implements the ISatellite interface. Specify values for the InputAddress and enable it as shown. The InputAddress is the queue that the satellite watches for messages.

public Address InputAddress => Address.Parse("targetqueue");

public bool Disabled => false;

When messages are received in the queue specified as the InputAddress, the satellite's Handle method will be invoked.

public bool Handle(TransportMessage message)
{
    // Implementation of what should occur when the message is received
    return true;
}

IAdvancedSatellite

To use this extension, declare a class that implements the IAdvancedSatellite interface. The IAdvancedSatellite offers additional customization. For example, as part of the receiving strategy, a custom error handling routine can be specified when there is a message processing error.

public Action<TransportReceiver> GetReceiverCustomization()
{
    // Customize the Failure Manager.
    satelliteImportFailuresHandler = new SatelliteImportFailuresHandler();
    return receiver => { receiver.FailureManager = satelliteImportFailuresHandler; };
}

SatelliteImportFailuresHandler satelliteImportFailuresHandler;

In the above example, the SatelliteImportFailuresHandler is a custom error handling routine that implements the IManageMessageFailures extension.