Dockerfile Cheat Sheet

FROM

Set base image for the build.

FROM ubuntu:20.04

Use specific version:

FROM node:14-alpine

Multi-stage build:

FROM node:14 AS build
FROM nginx:alpine

RUN

Execute commands during image build.

RUN apt-get update && apt-get install -y python3

Multiple commands:

RUN apt-get update && \
    apt-get install -y curl && \
    rm -rf /var/lib/apt/lists/*

COPY

Copy files from host to image.

COPY app.py /app/

Copy directory:

COPY ./src /app/src

Copy with permissions:

COPY --chown=user:group file.txt /app/

ADD

Copy files with additional features (extract archives, URL support).

ADD archive.tar.gz /app/

From URL:

ADD https://example.com/file.txt /app/

WORKDIR

Set working directory for subsequent instructions.

WORKDIR /app

Creates directory if it doesn't exist.

CMD

Default command to run when container starts.

CMD ["python3", "app.py"]

Shell form:

CMD python3 app.py

ENTRYPOINT

Configure container to run as executable.

ENTRYPOINT ["python3", "app.py"]

Combined with CMD:

ENTRYPOINT ["python3"]
CMD ["app.py"]

EXPOSE

Document which ports container listens on.

EXPOSE 80

Multiple ports:

EXPOSE 80 443

ENV

Set environment variables.

ENV APP_ENV=production

Multiple variables:

ENV APP_ENV=production \
    LOG_LEVEL=info

ARG

Define build-time variables.

ARG VERSION=1.0

Use in Dockerfile:

ARG NODE_VERSION=14
FROM node:${NODE_VERSION}

VOLUME

Create mount point for external volumes.

VOLUME /data

Multiple volumes:

VOLUME ["/data", "/logs"]

USER

Set user for running commands.

USER appuser

LABEL

Add metadata to image.

LABEL version="1.0"
LABEL description="My application"

Complete Example

FROM node:14-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
ENV NODE_ENV=production
USER node
CMD ["node", "server.js"]

Multi-Stage Build Example

FROM node:14 AS build
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

FROM nginx:alpine
COPY --from=build /app/dist /usr/share/nginx/html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]