Request-response message exchange coordinates distributed components through a request, receiver-side processing, and a response. Processing may cause a side effect before the response returns. section 4.1
A useful mental model separates the dialogue into five steps: the sender submits a request, the network delivers it, the receiver processes it, the receiver submits a response, and the network delivers that response. section 4.1
Reason about two distinct reliability dimensions:
- The network may reorder, drop, or duplicate messages; components may crash, recover, and forget volatile state while retaining durable state. section 4.1
Checkout as a multi-step exchange
An e-commerce checkout can involve charging a card, shipping goods, and issuing tickets. A failure must not leave an incorrect partial application: successful checkout should charge exactly once, while failed checkout should not charge at all. section 3.3.1
Figure 4.2 Step-by-step progression of the request-response dialogue
Trace the request-response dialogue as a concrete sequence of network and component events. section 4.1
