Software Architecture: The Hard Parts

Chapter 13. Contracts

Friday, April 15, 12:01

Addison met with Sydney over lunch in the cafeteria to chat about coordination between the Ticket Orchestrator and the services it integrated with for the ticket management workflow.

“Why not just use gRPC for all the communication? I heard it’s really fast,” said Sydney.

“Well, that’s an implementation, not an architecture,” Addison said. “We need to decide what types of contracts we want before we choose how to implement them. First, we need to decide between tight or loose contracts. Once we decide on the type, I’ll leave it to you to decide how to implement them, as long as they pass our fitness functions.”

“What determines what kind of contract we need?” Sydney said.

In Chapter 2, we began discussing the intersection of three important forces—communication, consistency, and coordination—and how to develop trade-offs for them. We modeled the intersectional space of the three forces in a joined three-dimensional space, shown again in Figure 13-1. In Chapter 12, we revisited these three forces with a discussion of the various communication styles and their trade-offs.

However much an architecture can discern a relationship like this one, some forces cut across the conceptual space and affect all of the other dimensions equally. If pursuing the visual three-dimensional metaphor, these cross-cutting forces act as an additional dimension, much as time is orthogonal to the three physical dimensions.

Figure 13-1. Three-dimensional ...