AWS API Gateway Fix-It Vol.1: The Complete Troubleshooting Map
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How to identify where an API Gateway request is failing—and jump directly to the Fix-It article that resolves that layer
Why This Hub Exists
When an API Gateway request fails, the hardest part is often not fixing the issue.
It’s answering this question:
Which layer is actually failing?
Is it:
- DNS?
- Domain routing?
- Stage deployment?
- Authorization?
- Integration permissions?
- Browser behavior?
API Gateway spans multiple layers of infrastructure, and its error messages frequently hide the real failure point. Debugging becomes fast and deterministic only when you identify the correct layer first.
This hub article provides a map of the entire request lifecycle and routes you to the exact Fix-It article that addresses each failure mode.
All articles referenced here are part of Volume 1 of the API Gateway Fix-It series.
The API Gateway Request Lifecycle (Mental Model)
Every request passes through the same high-level flow. Failures at different layers often surface as the same error, which is why guessing wastes time.
- DNS / Custom Domain
- Domain Routing & Base Path Mapping
- Stage Selection & Deployment
- Route Matching (Path + Method)
- Authorization (IAM / Authorizers / WAF)
- Integration Permissions
- Backend Execution
- Browser Enforcement (CORS)
Failure → Fix-It Routing Guide
Start with what you observe, not what you suspect.
1. You see: Missing Authentication Token OR 403 Forbidden
This means: You are struggling with the Routing vs. Authorization boundary. One means the route doesn't exist; the other means the route exists but you are blocked.
👉 Read:
Fix-It #1 — “403 Forbidden” vs “Missing Authentication Token”
(Routing traps, WAF, API keys, and distinguishing 403s from 404s)
2. You see: The same request behaves differently across APIs
This means: You may be applying REST API assumptions to an HTTP API (or vice versa).
👉 Read:
Fix-It #2 — REST API vs HTTP API
(Explicit config vs defaults, error semantics, auto-deploy)
3. You see: The client gets a 500, but Lambda never runs
This means: API Gateway is blocked at the Integration Permission boundary (The Trust Boundary).
👉 Read:
Fix-It #3 — Lambda Integration Permission Errors
(Resource policies, Source ARNs, aliases, IaC vs console behavior)
4. You see: Auth errors don’t make sense, and the backend never runs
This means: A Custom Authorizer may be short-circuiting the request or masking a crash.
👉 Read:
Fix-It #4 — Custom Authorizers Masking Real Failures
(403 vs 500 from authorizers, caching TTL traps, isolation strategy)
5. You see: It works in curl/Postman but fails in the browser with CORS
This means: The browser is blocking the response—often hiding a real 403 or 429 from the Gateway.
👉 Read:
Fix-It #5 — CORS Failures That Aren’t CORS
(OPTIONS preflight, MOCK integrations, Gateway Responses, browser traps)
6. You see: Console changes don’t affect runtime behavior
This means: You’re dealing with Stage Drift, undeployed snapshots, or canary traffic.
👉 Read:
Fix-It #6 — Stage Drift & Deployment Confusion
(Deployment History timestamps, canary deployments, REST vs HTTP deploys)
7. You see: It works on execute-api but fails on a Custom Domain
This means: The API is fine, but the Domain Routing or DNS is misconfigured.
👉 Read:
Fix-It #7 — Custom Domain & Base Path Mapping Failures
(DNS targets, propagation delays, base path mapping, stage removal)
A Simple Diagnostic Rule
Before touching code, IAM, or configuration, ask:
Did this request fail before or after the backend should have run?
- Before backend execution: Routing, auth, domains, stages, permissions, or CORS.
- After backend execution: Application logic (outside this series).
Every Fix-It article in this volume helps you answer that question precisely.
Conclusion
API Gateway failures feel mysterious only when you debug them out of order.
Once you identify the failing layer and apply the matching Fix-It, problems that once took hours collapse into minutes.
Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.
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