Dockerizing Next.js for production

Most Dockerfiles for Next.js you'll find online ship a 1.2 GB image, leak environment variables at build time, and rebuild every layer on a one-line change. They work on the demo. They don't work in production. This is the Dockerfile I actually run. Multi-stage, ~150 MB final image, build-time and runtime env vars cleanly separated, layer caching that survives a package.json change. I'll walk through every line, explain why each stage exists, and call out the four gotchas that account for most "