Some 20-30 years ago when designing a project, the architecture was thought to last. It was planned for 5+ years. But things change and even more so in our current days.

Evolutionary architecture accepts that change is inevitable and it tries to guide the change, aiming to prevent bit rot. It does this by leveraging a concept from Evolutionary Programming, namely the fitness function. The areas where bit rot can occur are called architecture concerns.

Architecture concerns

After a certain point, a solution is no longer concerned with just the clients' requirements. These concerns are called architecture concerns or cross cutting concerns, etc. There's many names for them really, but they all boil down to:

• Auditability
• Performance
• Security
• Requirements
• Data
• Legality
• Scalability

Fitness function

In Evolutionary architecture, a fitness function is any function/metric used to measure how good the solution is. Fitness functions are categorized based on:

Scope

• Atomic -> Running against a single concern.
• Holistic -> Running against multiple concerns.

Cadence

• Triggered -> By events. -> Unit testing, pipeline testing, QA testing.
• Continual -> more like periodic. Constantly checking the system at a particular interval.
• Temporal -> Making sure the code is keeping up with the times by failing older versions if libraries.