Dockerfile

A Dockerfile is a text document that contains a list of commands and instructions used to build a Docker image.

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Supported commands §

• FROM: Specifies the base image to start from (mandatory)
• MAINTAINER: Sets the author of the Dockerfile
• RUN: Executes commands
• ADD: Copies files into the filesystem of the image
• ENV: Sets environment variables
• ENTRYPOINT: Specifies the entry-point to use when running the container
• CMD: Defines the default command to run when the container starts
• EXPOSE: Maps a port into the container
• VOLUME: Creates a named volume
• WORKDIR: Sets the working directory for subsequent commands
• USER: Sets the user and group ID.

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Example §

# Ex: Dockerfile that creates a docker image for a node app 
 
FROM node:18-alpine
WORKDIR /app
COPY . .
RUN yarn install --production
CMD ["node", "src/index.js"]
EXPOSE 3000

docker build -t myimage .

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Passing dynamic arguments §

ARG PORT=3000 
FROM node:18-alpine 
WORKDIR /app 
COPY . . 
RUN yarn install --production CMD ["node", "src/index.js"] 
EXPOSE $PORT

docker build --build-arg PORT=4000 -t myimage .

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Related §

• Dockerfile vs Docker-compose

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Refs §

1. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/