NOTE
Refactoring
Refactoring as behavior-preserving design improvement, with test protection, incremental changes, observability, and boundaries between cleanup and architectural rewrite.
This is a historical learning note and may contain outdated or incomplete understanding.
1. What Refactoring Means
Refactoring changes internal structure while preserving externally observable behavior.
If behavior intentionally changes, that work includes a feature/migration in addition to refactoring.
2. Why Refactor
Good reasons include:
- reducing duplicated logic;
- clarifying ownership/boundaries;
- making changes safer;
- removing obsolete abstractions;
- improving testability.
Do not refactor only to make code match a preferred pattern.
3. Protect Behavior
Before risky changes, create confidence through:
- focused unit/integration tests;
- contract tests;
- production metrics/logging;
- shadow comparison where appropriate.
4. Prefer Small Steps
Move one responsibility at a time and keep the system deployable.
Large rewrites often recreate old bugs because hidden behavior was never documented.
5. Architectural Refactoring
For service/storage boundaries, use migration patterns such as strangler routing, compatibility adapters, dual reads/writes, and gradual traffic shifting.
Measure the outcome: simpler change path, fewer incidents, lower latency/cost, or reduced operational toil.