[Summary] – Fundamentals of Software Architecture An Engineering Approach – Part 9: Architecturally Significant

This is my learning note from the book Fundamentals of Software Architecture: An Engineering Approach written by Mark Richards and Neal Ford. All the contents are mostly distilled and copied from the book. I recommend you to buy this book to support the authors.

Many architects believe that if the architecture decision involves any specific technology, then it’s not an architecture decision, but rather a technical decision. This is not always true. If an architect makes a decision to use a particular technology because it directly supports a particular architecture characteristic (such as performance or scalability), then it’s an architecture decision.

According to Michael, architecturally significant decisions are those decisions that affect the structure, nonfunctional characteristics, dependencies, interfaces, or construction techniques.

Structure

The structure refers to decisions that impact the patterns or styles of architecture being used. An example of this is the decision to share data between a set of microservices. This decision impacts the bounded context of the microservice, and as such affects the structure of the application.

Nonfunctional characteristics

The nonfunctional characteristics are the architecture characteristics (“-ilities”) that are important for the application or system being developed or maintained. If a choice of technology impacts performance, and performance is an important aspect of the application, then it becomes an architecture decision.

Dependencies

Dependencies refer to coupling points between components and/or services within the system, which in turn impact overall scalability, modularity, agility, testability, reliability, and so on.

Interfaces

Interfaces refer to how services and components are accessed and orchestrated, usually through a gateway, integration hub, service bus, or API proxy. Interfaces usually involve defining contracts, including the versioning and deprecation strategy of those contracts. Interfaces impact others using the system and hence are architecturally significant.

Construction techniques

Finally, construction techniques refer to decisions about platforms, frameworks, tools, and even processes that, although technical in nature, might impact some aspect of the architecture.