Use Case #13: Zero-Downtime Migration

The client's Vercel bill was getting out of control. They wanted Netlify. The app had 2,000 daily active users. "Can you do it without downtime?"

Challenge accepted.

The Setup

A Next.js app running on Vercel with Supabase backend, custom domain, environment variables for 3 different API integrations, and Edge Functions that needed equivalent Netlify Functions.

What Claude Orchestrated

Phase 1: Parallel Deployment - Built and deployed to Netlify while Vercel stayed live. Same codebase, different platform. Verified all features worked on the Netlify preview URL.

Phase 2: Environment Parity - Audited all environment variables. Found 3 that were Vercel-specific (VERCEL_URL, etc.) and needed equivalents. Created Netlify equivalents and updated the code to check for both.

Phase 3: Edge → Serverless Conversion - Vercel Edge Functions have different APIs than Netlify Functions. Claude rewrote 4 functions to work on both platforms with a compatibility layer.

Phase 4: DNS Strategy - Planned the cutover: reduce TTL to 60 seconds 24 hours before, prepare both platforms to accept traffic, execute DNS switch, monitor for errors, keep Vercel running for stragglers with high TTL caches.

Phase 5: The Switch - At 2am (lowest traffic): DNS pointed to Netlify. Claude monitored error logs on both platforms. Caught one user whose browser cached the old IP - their requests still hit Vercel, which proxied to Netlify. Seamless.

The Result

The Safety Net

The best part: Claude kept Vercel running for 48 hours after migration. If anything went wrong, one DNS change would revert everything. It didn't, but knowing it could made the whole process stress-free.

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Migration completed January 2026. Client saved $400/month.