I picked up this book after hearing Neal Ford discussing software architecture on Software Engineering Radio. He spoke eloquently and engagingly on architecture “(capab)-ilities” and evolving systems. He elucidated many of my thoughts on the topic and mentioned the book. A year later I made the time to read the book and delve back into software architecture. This review covers background information on the book, my thoughts, and a recommendation. You should skip to the end if you’re purely interested in the recommendation.
We explore the ideas behind continual architecture: building architectures that have no end state and are designed to evolve with the ever-changing software development ecosystem, and including built-in protections around important architectural characteristics.
Building Evolutionary Architectures’ goal is to demonstrate the value in building, and how to implement, evolvable systems that fit today’s dynamic software landscape.
The process starts with identifying “-ilities” (their word for characteristics such as “affordability” or “flexibility”), then balancing the “-ilities” across dimensions such as technical implementations or data storage, and verifying the “-ilities” in the relevant dimensions with fitness functions. Think of fitness functions as architecture tests. Now bundle the whole thing up as part of the deployment pipeline and you’ve got “continuous architecture” that evolves with guidance from the fitness functions.
The author’s make their case with examples and hypothetical case studies. The author use a theoretical company called Penultimate Widgets to demonstrate problems and throughout the text. Readers will likely relate to hypothetical problems since they mirror frustration in any software team.
Many of the book’s ideas were not new to me. It seems natural to me that software architecture is the discipline of managing technical trade-offs, business outcomes, team structure, and hedging against unknown unknowns.
I balanced this equation at Saltside best I could. I lead the team in restructuring our quasi monolithic ball of mud into something more service oriented / micro service architecture. We did this because meaningful product development was too time consuming. This is a case and point example of what happens when a team fails to evolve with time. Interestingly enough, the restructuring steps we took are mentioned in the migration case studies in later chapters so I guess we did something right.
I did not make all the right decisions in that project. A few years of long tail experience revealed new dimensions and brittle integration points. Building Evolutionary Architectures may have helped cull those effects, but that project completed years before the book was published.
Personally, I did not get much out of the ideas discussed in the book and few technical examples were not substantive enough for my taste. However, I did appreciate the new vernacular because it provides a great way to communicate aspects in software architecture.
The authors introduce catchy vernacular. This isn’t a slight. Their vernacular is well thought out and useful. Let me begin with “-ilities” — sort of like capabilities. Software architectures balance “-ilities” such as “scalability”, “malleability”, or “debugability”. I used the term “concerns” to cover these. Author’s sold me on “-ilities” because it stands out from a myriad of other overloaded terms.
They also introduce terms for classifying fitness functions. These resonated with me the most since they enforce the trade-off spectrum in all architecture decisions. They are (as quoted):
- Key: These dimensions are critical in making technology or design choices. More effort should be invested to explore design choices that make change around these elements significantly easier. For example, for a banking application, performance and resiliency are key dimensions.
- Relevant: These dimensions need to be considered at a feature level, but are unlikely to guide architecture choices. For example, code metrics around the quality of code base are important but not key.
- Not Relevant: Design and technology choices are not impacted by these types of dimensions. For example, process metrics such as cycle time (the amount of time to move from design to implementation, may be important in some ways but is irrelevant to architecture. As a result, fitness functions for it are not necessary).
It’s easy for me, in retrospective, to see what I classified as key, relevant, and not relevant. Hopefully these terms stick with me for use in future discussions.
I did pick up one powerful new idea. The author’s propose a form of automatic dependency upgrades that minimizes technical debt. Dependencies are marked as as “fluid” or “guarded”. Roughly speaking, the deployment pipeline upgrades to the newest major or minor version of fluid dependencies. If everything passes, then dependencies automatically update. If they fail, then the process retires with a minor version bump. If they fail again, then repeat with a patch version bump. If they still fail, then they become “guarded” and requiring manual action from engineers to restore the fluid label.
I think this practice would pay dividends for framework level dependencies. They are the most painful because of higher coupling. If you skip too many, then it becomes a massive task to get up-to-date. Automated upgrades would mitigate technical debt and increase security. Unfortunately there are no such tools available right now for fluid and guarded dependencies.
Highlights & Take-Aways
Software architects should pay attention to how work is divided and delegated to align architectural goals with team structure.
The author’s devote a delightful amount of time to discussing the connection between software architecture and team structure. Don’t discount how architecture choices impact the flow of work and the other way around. This is a powerful feedback loop which can destroy companies!
As developers restructure architecture, their first step should be to remove the historical design compromises that manifest as technical debt.
This is not obvious but important. It’s also nice to see that technical debt is the manifestation of design choices (or “-ilities” selection) that have become outdated.
I recommend you skip the book. Instead visit the author’s websites, listen to their conference talks, or podcast appearances. If you think that software architecture should be flexibility and change over time, and you have hands on experience in this domain then you may not get much value out of the book. However, if you may find the book valuable if you’ve never given high level architecture design much thought. Even so, I think roughly the same information is available through other free mediums.