This sample was created during Greg Young's Advanced CQRS & DDD Workshop in London Nov 7-10 of 2017.
The course started out given a really simple scenario. We're basically running a restaurant. So we have 4 basic actors in our system. The Waiter which takes orders from customers, the Cook which takes an order and prepares the food. Then an Assistant Manager which determines the price for individual line items and finally a Cashier which will handle actual payment for an order.
Given these four basic actors, we started implementing with composition of these actors as a pipeline through IHandleOrder interface which exposes one Handle(Order) method. This way we can send messages through a pipeline from the Waiter, to the Cook, to the Assistant Manager and finally to the Cashier. Later in the workshop we've re-implemented some of this logic in the form of a topic based Pub/Sub bus.
Conceptually you can think of each of these 4 actors as being implemented as a micro service, where messages passed between them are sent via an actual broker.
- Composition of logic
- Process Manager(s)
- Chaos (Seemingly random dropping messages vs. delivering messages twice)
- Idempotent message handling
- Sending messages to future self
- Weak schema between services (don't lose message elements when serializing/deserializing)
- Using CorrelationId and CausationId on messages