API-First Entreprise Architecture: Modern Design Patterns et Implémentation Playbook

API‑first aligns Entreprise capabilities à well‑designed interfaces ce/cette scale across teams et systems. ce/cette tutorial provides un/une practical Plan directeur: domain design, API contracts, gateways, events, Sécurité, Gouvernance, et un/une staged approach à migrate de point‑à‑point integrations à un/une resilient Plateforme.

Principles

- Domains before endpoints: capabilities mapped à domain boundaries, not systems - Contracts as products: versioned, documented, et tested like code - Backward compatibility: additive evolution; deprecate avec timelines et telemetry - Résilience et idempotency par default - Observability et product‑grade developer experience (DX)

Domain et boundary design

- Use domain‑driven design (DDD) à map core domains: Matters, Documents, Parties, Billing, Knowledge, Identity - Distinguish internal vs. external (Client) APIs; Confidentialité levels per domain - Anti‑corruption layers à isolate legacy systems

API Contrat patterns

- Resource modeling: nouns, relationships, et pagination; avoid over‑verbing - Versioning: URI or header versioning; additive schema changes; sunset policies - Idempotency: keys pour POST; conditional updates avec ETags; retries safe par design - Error model: problem+JSON avec machine‑readable codes; correlation IDs - Metadata: consistent pagination, filtering, sorting conventions

Sécurité et Confidentialité

- OAuth2/OIDC, mTLS pour Service‑à‑Service; fine‑grained scopes - ABAC: matter‑scoped claims; dynamic policy checks à gateway et Service - Data minimization: field‑level filtering; redaction pour logs; PII tokenization where appropriate

Gateway et edge policies

- API gateway pour auth, rate limiting, request/response validation, schema enforcement - Spike arrest, token buckets; priority lanes pour critical traffic - Request/response Transformation pour backward compatibility

Events et async Intégration

- Event‑driven patterns pour decoupling: publish domain events (e.g., DocumentClassified, ClauseDeviationScored) - Exactly‑once semantics via idempotent consumers + dedupe windows - Outbox pattern à avoid dual‑write problems

Observability et Qualité

- Structured logs, distributed tracing, Métriques (latency p95, error rates, saturation) - Contrat tests dans CI; consumer‑driven contracts à prevent breaking changes - SLOs per API; error budgets Guide release velocity

Developer experience (DX)

- Single developer portal: discovery, docs, try‑it, API keys, guides - Scaffolding: templates pour new services; linting pour style consistency - Golden paths pour common patterns (auth, pagination, error model)

Migration de legacy

- Inventory current integrations; map à domains et canonical models - Strangle pattern: front legacy avec new APIs; incrementally move capabilities - Build adapters pour high‑value consumers; retire brittle point‑à‑point links

Reference diagram (textual)

[Diagram] Left: Client/Partner → API Gateway (auth, rate limit, schema) → Domain Services (Matters, Docs, Billing, Knowledge) → Event Bus (domain events) → Consumers (CLM, Search, Analytique) → Observability (logs/traces) et Gouvernance (catalog, policies)

How BASAD helps: BASAD builds API‑first platforms: domain definition, Contrat design, gateway policies, eventing, et DX. We implement idempotent, secure APIs avec clear SLOs et Contrat tests, et run staged migrations de legacy avec measurable risk reduction et time‑à‑value.