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Builds

Push code; get a container. Here is exactly what happens in between.

Build strategy

Buildfyio picks the first strategy that applies:

Priority	Strategy	When
1	`Dockerfile` in your app directory	You opted into full control — we build it verbatim and never override it.
2	Workspace build	The app is a pnpm / yarn / npm workspace member — installed and built from the repository root, like locally.
3	Automatic detection (Nixpacks)	25+ runtimes: package manager, build and start commands detected from the repo.
4	Framework template	Fallback if automatic detection cannot build — a curated per-framework image.

Build-time environment

Every environment variable you define reaches the build. Non-secret values are injected as plain build environment; secret-marked values are mounted with BuildKit secret mounts, so they are available to the build process (a Next.js prerender reading an API key, for instance) without ever being written into an image layer. Rotating a secret automatically invalidates the build cache for that step.

Variables whose names look sensitive (*_SECRET, *_API_KEY, *_PASSWORD, *_SERVICE_KEY, *_PRIVATE_KEY, …) are treated as secrets automatically, even if you did not mark them.

Caching

Layer cache is kept in a private registry per project. In practice: a rebuild with unchanged dependencies skips the install step entirely — cache-warm rebuilds typically run in under a minute.

Ports

The detected port comes from your framework (3000 for Next.js, 4321 for Astro, …). If your start command names an explicit port — next start --port 3002, -p 8080, PORT=5000 node server.js — that port wins everywhere: health checks, routing, and the container contract. Your app should listen on 0.0.0.0, not localhost.

Framework notes

Astro

Static Astro publishes straight to the edge — no container, instant serves.
SSR Astro (an adapter in astro.config) builds and runs as a container.
Repos configured with @astrojs/vercel run unchanged: the build swaps in a runnable server adapter automatically. Your repository is never modified.

Prisma

prisma generate runs automatically when a schema is present — including in pnpm workspaces where package postinstall scripts are blocked by default.

devDependencies

Build tooling that lives in devDependencies (Tailwind, Vite plugins, type checkers) is always installed at build time — production pruning happens after the build, not before it.

Bring your own Dockerfile

# Detected automatically when apps/api/Dockerfile exists
FROM node:20-alpine
WORKDIR /app
COPY . .
RUN npm ci && npm run build
EXPOSE 3000
CMD ["node", "dist/main.js"]

Monorepos & workspaces →Troubleshooting builds →Environment variables →