vercel-advanced-troubleshooting

# Vercel Advanced Troubleshooting ## Overview Diagnose hard-to-find Vercel issues: intermittent cold start failures, edge function crashes, region-specific behavior, function bundling problems, and serverless concurrency issues. Uses systematic isolation, request tracing, and Vercel-specific debugging techniques. ## Prerequisites - Vercel CLI with access to production logs - Familiarity with `vercel-common-errors` (standard debugging) - `curl` and `jq` for API inspection - Access to deployment inspection tools ## Instructions ### Step 1: Request-Level Tracing ```bash # Trace a single request through Vercel's edge network curl -v https://yourdomain.com/api/endpoint 2>&1 | grep -E "x-vercel|cf-ray|age|cache" # Key headers to check: # x-vercel-id: <region>::<function-id> — which region served the request # x-vercel-cache: HIT/MISS/STALE — edge cache status # x-vercel-execution-region: iad1 — function execution region # age: 45 — seconds since edge cached the response # x-matched-path: /api/endpoint — routing match result ``` ### Step 2: Cold Start Investigation ```typescript // Instrument cold start timing in your function let coldStart = true; const initTime = Date.now(); export default function handler(req, res) { const isCold = coldStart; coldStart = false; const handlerStart = Date.now(); // ... your logic ... res.setHeader('x-cold-start', String(isCold)); res.setHeader('x-init-duration', String(handlerStart - initTime)); res.json({ coldStart: isCo...