Dev
Mock Dockerfile Generator
A Dockerfile that puts COPY . . before npm ci busts the dependency cache on every code change, slowing down every rebuild. Getting layer ordering and image size right requires knowing a few non-obvious conventions. This tool generates a best-practice Dockerfile for one of three stacks, demonstrating those conventions concretely. Choose "node" for a Node 20 Alpine image that copies package*.json first, runs npm ci --omit=dev (skipping devDependencies), then copies the rest of the source and starts with node server.js. Choose "python" for a Python 3.12 Slim image that installs from requirements.txt before copying source code. Choose "go" for a multi-stage build: a golang:1.22 build stage that compiles the binary, followed by a minimal distroless base image that only copies the compiled binary — no compiler or build tools in the final image. Copy the output into a Dockerfile at your project root. Adapt the EXPOSE port, the entry command, and the base image tag to your application. For production, pin base image versions (node:20.15-alpine, not node:20-alpine) to avoid unexpected updates.
How to use
- Choose your options above
- Click Generate
- Copy your result
Detailed instructions
- Choose your stack.
- Click Generate to produce a Dockerfile.
- Copy it into your project root.
- Adapt the base image and commands.
Use Cases
- •Learning Dockerfile syntax
- •Scaffolding a container build
- •Documenting a Docker setup
- •Demoing container conventions
- •Starting a new project
Tips
- →Copy dependencies before the code.
- →Order layers least-changed first.
- →Use multi-stage builds for lean images.
- →Adapt the base image to your needs.
FAQ
what does each stack option generate
"node" generates a Node 20 Alpine image with npm ci --omit=dev and CMD ["node", "server.js"]. "python" generates a Python 3.12 Slim image with pip install from requirements.txt and CMD ["python", "app.py"]. "go" generates a two-stage build: golang:1.22 compiles the binary, then a distroless base image runs it — no build tools in the final image.
why copy dependencies before the rest of the source code
Docker caches each layer. By copying only the dependency manifest (package*.json or requirements.txt) and running the install step before copying the rest of the source, the slow install layer is reused on rebuilds as long as dependencies have not changed. Copying all source first invalidates that layer on every code change, forcing a reinstall every time.
what is a multi-stage build and why use one
A multi-stage build uses multiple FROM stages in one Dockerfile. The Go example uses a full golang image to compile the binary, then copies only the compiled binary into a minimal distroless image for the final stage. The compiler, module cache, and build tools are discarded, producing a much smaller and more secure final image.
what is the difference between cmd and entrypoint
CMD specifies the default command and arguments, which can be overridden at docker run time. ENTRYPOINT sets the fixed executable that always runs; arguments to docker run are passed as arguments to it. The Node and Python examples use CMD; the Go example uses ENTRYPOINT because the binary is the sole process. Both forms accept JSON array syntax for reliable argument handling.
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