Shadow slot always ON
Continuous 1% of prod traffic on master. Every merge ships a shadow deploy — catch regressions before promoting.
shadow-canary
Shadow-permanent 1% + SLO-gated canary ramp. For Next.js on Vercel.
What you get
Canary with auto-rollback
Merge master into production. New deploy starts at 0%, ramps +4%/15min if SLO stays green. Auto-rollback on failure.
Zero-lockin routing
Edge Config + Next.js middleware. No third-party SDK. Change the ramp curve in YAML.
Why this pattern
- Zero-downtime releases with stateful rollback to the previous deploy.
- Sessions sticky by cookie — no user hops between versions mid-checkout.
- Config-driven — Edge Config updates propagate in 60s or less, no redeploy.
- Works with any Next.js 13.4+ App Router project.
Not for you if
- You need per-user feature flags — use LaunchDarkly or Statsig instead.
- Your stack is not Next.js on Vercel.
- You want A/B testing with metrics attribution — this is reliability, not experimentation.