Create Dockerfile

Create Dockerfile

Write a production-ready Dockerfile for general-purpose application projects.

When to Use

• Containerizing a Node.js, Python, Go, Rust, or Java application
• Creating a consistent build/runtime environment
• Preparing an application for cloud deployment or Docker Compose
• No existing Dockerfile in the project

Inputs

• Required: Project language and entry point (e.g., npm start, python app.py)
• Required: Dependency manifest (package.json, requirements.txt, go.mod, Cargo.toml, pom.xml)
• Optional: Target environment (development or production)
• Optional: Exposed ports

Procedure

Step 1: Choose Base Image

Language	Dev Image	Prod Image	Size
Node.js	node:22-bookworm	node:22-bookworm-slim	~200MB
Python	python:3.12-bookworm	python:3.12-slim-bookworm	~150MB
Go	golang:1.23-bookworm	gcr.io/distroless/static	~2MB
Rust	rust:1.82-bookworm	debian:bookworm-slim	~80MB
Java	eclipse-temurin:21-jdk	eclipse-temurin:21-jre	~200MB

Expected: Select the slim/distroless variant for production images.

Step 2: Write Dockerfile (by language)

Node.js

FROM node:22-bookworm-slim

RUN groupadd -r appuser && useradd -r -g appuser -m appuser

WORKDIR /app

COPY package.json package-lock.json ./
RUN npm ci --omit=dev

COPY . .

USER appuser
EXPOSE 3000
CMD ["node", "src/index.js"]

Python

FROM python:3.12-slim-bookworm

RUN groupadd -r appuser && useradd -r -g appuser -m appuser

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

USER appuser
EXPOSE 8000
CMD ["python", "app.py"]

Go

FROM golang:1.23-bookworm AS builder

WORKDIR /src
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o /app/server ./cmd/server

FROM gcr.io/distroless/static
COPY --from=builder /app/server /server
EXPOSE 8080
ENTRYPOINT ["/server"]

Rust

FROM rust:1.82-bookworm AS builder

WORKDIR /src
COPY Cargo.toml Cargo.lock ./
RUN mkdir src && echo "fn main() {}" > src/main.rs && cargo build --release && rm -rf src

COPY . .
RUN touch src/main.rs && cargo build --release

FROM debian:bookworm-slim
RUN apt-get update && apt-get install -y ca-certificates && rm -rf /var/lib/apt/lists/*
COPY --from=builder /src/target/release/myapp /usr/local/bin/myapp
EXPOSE 8080
ENTRYPOINT ["myapp"]

Java (Maven)

FROM eclipse-temurin:21-jdk AS builder

WORKDIR /src
COPY pom.xml .
RUN mvn dependency:go-offline -B
COPY src ./src
RUN mvn package -DskipTests

FROM eclipse-temurin:21-jre
COPY --from=builder /src/target/*.jar /app/app.jar
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "/app/app.jar"]

Expected: docker build -t myapp . completes without errors.

On failure: Check base image availability and dependency installation commands.

Step 3: ENTRYPOINT vs CMD

Directive	Purpose	Override
ENTRYPOINT	Fixed executable	Override with --entrypoint
CMD	Default arguments	Override with trailing args
Both	ENTRYPOINT + default args via CMD	Args override CMD only

Use ENTRYPOINT for compiled binaries with a single purpose. Use CMD for interpreted languages where you might want docker run myapp bash.

Step 4: Create .dockerignore

.git
.gitignore
node_modules
__pycache__
*.pyc
target/
.env
.env.*
*.md
!README.md
.vscode
.idea
Dockerfile
docker-compose*.yml

Expected: Build context excludes development artifacts.

Step 5: Add Non-Root User

Always run as non-root in production:

RUN groupadd -r appuser && useradd -r -g appuser -m appuser
USER appuser

For distroless images, use the built-in nonroot user:

FROM gcr.io/distroless/static:nonroot
USER nonroot

Step 6: Build and Verify

docker build -t myapp:latest .
docker run --rm myapp:latest
docker image inspect myapp:latest --format '{{.Size}}'

Expected: Container starts, responds on the expected port, runs as non-root.

On failure: Check logs with docker logs. Verify WORKDIR, COPY paths, and exposed ports.

Validation

• docker build completes without errors
• Container starts and application responds
• .dockerignore excludes unnecessary files
• Application runs as non-root user
• Dependencies are copied before source code (cache efficiency)
• No secrets or .env files baked into the image

Common Pitfalls

• COPY before dependency install: Invalidates the dependency cache on every code change. Always copy the manifest file first.
• Running as root: Default Docker user is root. Always add a non-root user for production.
• Missing .dockerignore: Sending node_modules or .git into the build context wastes time and disk.
• Using latest tag for base images: Pin to specific versions (e.g., node:22.11.0) for reproducibility.
• Forgetting --no-cache-dir: Python pip caches packages by default, bloating the image.
• ADD vs COPY: Use COPY unless you need URL download or tar extraction (ADD auto-extracts).

Related Skills

• create-r-dockerfile - R-specific Dockerfile using rocker images
• create-multistage-dockerfile - multi-stage patterns for minimal production images
• optimize-docker-build-cache - advanced caching strategies
• setup-compose-stack - orchestrate the containerized app with other services