Multistage Dockerfile Builder

A carelessly built Docker image carries everything used to build it: compiler, development dependencies, package manager cache, source code. That bloats the image, lengthens deployment and widens the attack surface — every extra tool in there is another tool in the hands of anyone who gets inside the container.

A multi-stage build cuts that off at the root. A first stage, the builder, installs everything and compiles. A second stage starts from a clean image and copies only the result, with COPY --from=builder. Everything left behind in the first stage is discarded and never reaches the final image. Enter the Node version and the page generates the Dockerfile with both stages already wired up.

The order of instructions in the generated file is not accidental. package.json is copied and dependencies installed before the rest of the code, because each instruction becomes a layer with its own cache: changing one line of source does not invalidate the npm ci layer, and the next build reuses what was already there. Swapping those two lines makes the whole install run again on every change.