architecture-fitness-functions

Architecture Fitness Functions

Use when architecture quality should become observable, testable, or CI-enforced.

Rule Shape

Each rule needs: intent, scope, owner, signal, mechanism, pass condition, cadence, failure action, exception path, related ADR/principle, protected quality attribute, and tradeoff.

Cadence: local, pre-commit, ci, release, scheduled, production.

Rollout: measure -> warn -> enforce for legacy systems.

Common Guardrails

• Dependency direction: domain, UI, adapters, shared packages, and apps import only allowed layers.
• Cycle prevention: package, namespace, module, service, or workspace cycles.
• Boundary API: imports only through public entry points.
• Data ownership: one bounded context owns writes for a table/topic/entity family.
• Runtime coupling: sync calls, queues, cache, external APIs follow approved directions.
• Observability/resilience: critical flows expose logs/metrics/traces/health checks and timeout/retry/fallback/idempotency policies.
• Deployment safety: migration order, feature flags, rollback readiness, compatibility windows.
• Documentation drift: architecture-changing code links ADRs, diagrams, ownership docs.
• Ownership topology: architecture-significant paths have owner coverage; cross-owned changes request both owner paths or documented waiver.
• Change amplification: co-change hotspots or touched-file width stay below agreed thresholds.
• Conformance/metrics: forbidden edges stay absent, required edges/docs exist, cycles stay absent, high fan-out requires review.

Tooling Preference

Prefer existing project tools; add dependencies only when the boundary is important and cost is explicit.

Examples: ArchUnit/jQAssistant, NetArchTest/NDepend, dependency-cruiser/eslint/Nx graph, import-linter/pytest checks, go list, cargo metadata/clippy, SwiftPM target graph/XCTest.

Lightweight start:

python3 scripts/architecture_probe.py <repo-path> --json
python3 scripts/architecture_probe.py <repo-path> --json --policy <policy.json>

The probe covers top-level coupling, instability, cycles, runtime signals, ownership topology, and simple policy checks.

Workflow

1. State architecture principle in one sentence.
2. Pick the smallest measurable signal.
3. Choose cheapest existing mechanism.
4. Name protected quality attribute and tradeoff.
5. Define pass/fail threshold and exception policy.
6. Tie to ADR/rule and rollout mode.

Output

Use architecture_intelligence.fitness_plan.v1 or a compact table: Rule, Signal, Tool, Pass condition, Cadence, Owner.

Do not create brittle gates that block delivery without migration path.