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API Gateways and Contracts ​

API Gateways and Contracts Graphics Coverage ​

Primary chapter graphic: API Gateway Request Policy Flow, API Design Control Surface, API Development Learning Map, REST API Design Practices, API Security Control Checklist, API Development Learning Map, API Performance Control Flow, MCP and API Integration Difference, API and SDK Usage Boundary, Good API Design Principles, REST API Constraint Map. Accepted graphics: 11. Reviewed non-signal pages: 7. Open graphics in review: 0. QA status lives in graphics audit and visual review ledger.

Corpus pages: p. 10-11, p. 16-17, p. 31, p. 65-66, p. 71, p. 73, p. 76, p. 114, p. 116, p. 135, p. 143-144, p. 168-169, p. 191, p. 232, p. 234-235, p. 238, p. 259, p. 270-271, p. 332-333, p. 339-340, p. 361, p. 376, p. 380-381, p. 403, p. 411-412 Coverage: 36 pages; low-confidence extraction ranges: p. 10-11, p. 16-17, p. 361, p. 376, p. 380-381

This chapter is part of Marius's owned architecture build corpus. The text routes decisions; durable implementation signal is carried by accepted graphics, reviewed non-signal decisions, and the linked QA audit.

Chapter Visuals ​

Accepted graphics carry the canonical design signal for this chapter. Each selected source page is either accepted as a graphic or explicitly marked non-signal in the source-faithful ledger. Review and QA state live in visual inventory, visual review ledger, and graphics audit.

API Gateway Request Policy Flow ​

API Gateway Request Policy Flow

API Design Control Surface ​

API Design Control Surface

API Development Learning Map ​

API Development Learning Map

API Security Control Checklist ​

API Security Control Checklist

REST API Design Practices ​

REST API Design Practices

API Development Learning Map ​

API Development Learning Map

API Performance Control Flow ​

API Performance Control Flow

MCP and API Integration Difference ​

MCP and API Integration Difference

API and SDK Usage Boundary ​

API and SDK Usage Boundary

Good API Design Principles ​

Good API Design Principles

REST API Constraint Map ​

REST API Constraint Map

Open Review Queue ​

  • none

Reviewed Non-Signal Pages ​

  • API Gateways And Contracts: API Gateway + Rate Limiting Map: source p. 135; batch 01; status non-signal/reviewed; ledger reason in visual-review-ledger.json
  • API Gateways And Contracts: API Gateway + Rate Limiting Map: source p. 361; batch 01; status non-signal/reviewed; ledger reason in visual-review-ledger.json
  • API Gateways And Contracts: API Gateway + Rate Limiting Map: source p. 11; batch 02; status non-signal/reviewed; ledger reason in visual-review-ledger.json
  • API Gateways And Contracts: API Gateway + Rate Limiting Map: source p. 31; batch 02; status non-signal/reviewed; ledger reason in visual-review-ledger.json
  • API Gateways And Contracts: OAuth + HTTP Map: source p. 65; batch 04; status non-signal/reviewed; ledger reason in visual-review-ledger.json
  • API Gateways And Contracts: Rate Limiting + Authentication Map: source p. 271; batch 08; status non-signal/reviewed; ledger reason in visual-review-ledger.json
  • API Gateways And Contracts: Stream Map: source p. 71; batch 09; status non-signal/reviewed; ledger reason in visual-review-ledger.json

Use When ​

  • Two systems need a stable interface with clear inputs, outputs, errors, limits, and version behavior.

Avoid When ​

  • Both sides change together and a function call is simpler.

Core Model ​

  • An API is a contract boundary. Gateways centralize cross-cutting policy, but the contract still belongs to the product domain.
  • Prefer explicit ownership over accidental coupling. Every boundary should say who owns correctness, cost, data, recovery, and change.
  • Use corpus page pointers for inspection, and keep the chapter notes focused on reusable design decisions.

Implementation Guidance ​

  • Specify schema, authentication, authorization, pagination, idempotency, rate limits, and deprecation rules together.
  • Write the smallest useful design note: purpose, inputs, outputs, state, failure behavior, observability, and rollback.
  • Choose the first implementation that can be tested against the real workflow without hiding a known production risk.

Tradeoffs ​

  • A gateway reduces duplication, but too much business logic inside it creates a second application.
  • Centralization reduces duplicated work but can become a bottleneck when every team needs exceptions.
  • Specialized infrastructure helps at scale, but it must earn its operational cost.

Failure Modes ​

  • Retries create duplicate side effects because the create path has no idempotency key.
  • The diagram shows boxes but not ownership, retry behavior, data freshness, or user-visible failure.
  • The system has no proof path for the highest-risk assumption.

Decision Checklist ​

  • Add contract tests for the highest-risk request and the most common error response.
  • Name the owner, source of truth, timeout, retry policy, and evidence that the path works.
  • Add one regression check for the failure mode most likely to recur.

Neutral Automation Examples ​

  • A document service exposes one create request and returns a job ID when rendering will outlive the HTTP timeout.
  • A neutral internal automation starts with fixtures, then adds credentials, permissions, and production scheduling only after the boundary is tested.
  • A customer-facing workflow keeps irreversible actions behind explicit approval until metrics show it is safe to automate further.