When building systems using the request/response pattern the
Reply method, exposed by the
IBus interface, is used to reply to the sender of the incoming message.
Reply method can be used inside a
Saga and it is important to understand that it can have a different semantic, otherwise it can lead to some unexpected behaviors.
Replymethod always delivers the message to the sender address of the incoming message.
The following diagram details a scenario where two sagas and an integration endpoint utilize the request/response pattern to communicate. In red are highlighted the replies.
The reason why a call to
Reply<ShipOrder>() sends a message to the
Shipment Gateway is that it is invoked in the context of handling the
ShipmentReserved message, and the return address of
In the context of a
Saga it is not always clear, at a first look, who is the sender of a message. In the above sample when handling the expired
ShipmentReservation timeout the sender of the message is the
Delivery Manager endpoint, so in this case a
Reply would be delivered to the
Delivery Manager, that is not necessarily desired.
ReplyToOriginator makes it clear to NServiceBus that the message to be delivered to the endpoint that was the originator of the saga.