npm

A two-phase upgrade playbook: npm inside the running container plus an automatic custom-image fallback, verified against the version the app actually serves.

TL;DR: After upgrading 9router, the endpoint still served the old version because the container ran code baked into the image, not the freshly installed npm package. The rewritten playbook uses a two-phase approach: cheap in-container installs first, then building an image from source, with served-version verification, health checks, and automatic rollback. Running serial: 1 keeps failures contained to one host.

Vercel infers the package manager from the lockfile, not package.json. One leftover pnpm-lock.yaml failed the deploy with ERR_PNPM_OUTDATED_LOCKFILE.