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Dockerfile Builder Guide

Build a Dockerfile from a form, with multi-stage presets for Node, Python, Go, Nginx and more.

The difference between a build stage and a runtime stage becomes clearer when you compare their instructions. Dockerfile Builder lays out both stages as editable Dockerfile text. Presets cover Node, Python, Go, static sites on Nginx, PHP and Java Maven builds; each can be adjusted through the base image, workdir and individual instructions. Multi-stage builds get a builder stage and copy the artifacts into the runtime image. The output is built in the page and can be copied or downloaded as a Dockerfile.

Generate a Node image from a preset

Open the Preset list and choose Node.js (build + run). The Dockerfile panel fills in immediately, and the toolbar reports the line count. Read it top to bottom: an # syntax line, a build stage that copies package*.json, runs npm ci and npm run build, then a runtime stage that copies dist out of the build stage with COPY --from=build, runs the production install, exposes port 3000 and ends with a CMD.

Now switch Preset to Go (static binary) and compare: the runtime stage uses a distroless base and an ENTRYPOINT instead of a CMD, because a Go binary needs no package manager at runtime. Tick and untick Multi-stage build and watch the Build stage fields appear and disappear from the form. Turn on Join RUN commands with && to see several commands collapse into one layer, and turn off Add section comments to drop the # headings.

Change Base image to something wrong, such as empty it, and the status asks you to pick one. Put a bad value like 3000, 8080 in EXPOSE and it becomes EXPOSE 3000 8080. Copy takes the text and Download saves it as a file literally named Dockerfile.

Where your input goes

Processing runs in your browser. The tool does not upload your input to ilham.dev.

For more background, read Docker Basics.

Questions you might have

When is a multi-stage build worth it?
When the tools that build the app are not the tools that run it: a Go binary needs the Go toolchain only at build time, and a Node app needs dev dependencies only to bundle. The runtime image then carries just the artifact, which is smaller and has fewer things to patch.
What is the difference between ENTRYPOINT and CMD?
ENTRYPOINT is the program that always runs; CMD supplies default arguments that a docker run command can override. If you set both, put the executable in ENTRYPOINT and the defaults in CMD. The page writes either as JSON when the value starts with [, otherwise as shell form.
Why order the instructions this way?
Docker caches one layer per instruction and rebuilds from the first changed layer onward. Copying dependency manifests and installing before copying the rest of the source means a code change does not re-install dependencies. Keep the slow, rarely-changing steps near the top.
COPY or ADD?
The page emits COPY, which is what you almost always want: it copies files and directories. ADD also unpacks local tarballs and can fetch URLs, which is convenient but surprising, so use it deliberately rather than by default.