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Dockerfile

Dockerfile
# Always specify the base image. It can be an official image from Docker Hub or a custom image from a private registry.
FROM ubuntu:22.04
# Run any terminal commands during the build
RUN sudo apt update && sudo apt install nodejs && sudo apt install npm
# Set the working directory to define an explicit location for command execution inside the Dockerfile
WORKDIR /app
# Copy the entire contents of the folder where the Dockerfile is located into /app in the image
COPY . /app
# ADD can download a file or extract an archive
# Set environment variables
ENV NODE_ENV=production
# ARG can be specified at build time (docker build --build-arg user=node_user). Stays in history, not for secrets (docker history)
# For securely passing sensitive data, use Docker volumes instead
# Default value is 'deploy' (can be omitted)
ARG user=deploy
# Run as the system or another user (specified in ARG)
USER $user
# Expose a port from the container
EXPOSE 8080
# At the end, start the application with ENTRYPOINT/CMD
ENTRYPOINT ["node", "/app/app.js"]
# CMD ["node", "/app/app.js"]
# CMD can be overridden when starting a container

Multi-stage build​

Dockerfile
# Build the project on the Node.js platform
FROM node:lts-alpine as build-stage
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
# Run the application on the server
FROM nginx:stable-alpine as production-stage
COPY --from=build-stage /app/dist /usr/share/nginx/html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

Excluding files from the build with .dockerignore​

# Files or folders whose names start with temp and are located in any first-level folder
*/temp*
# For second-level folders
*/*/temp*
# Files and folders from the root of the image whose names start with temp, are five characters long, and the last character can be anything
temp?
# Build an image in the current folder
docker build .
# Specify a file
docker build -f containers/dockerfile-mode-1 .
# Can download, extract, and build an image (bzip2, gzip, xz)
docker build -f ctx/Dockerfile http://server/ctx.tar.gz
# Build without context
docker build - < Dockerfile
# First, after your login you have to tag your image before pushing:
docker tag image_name YOUR_DOCKERHUB_NAME/image_name
# then, you have to push it.
docker push YOUR_DOCKERHUB_NAME/image_name

Best practices​

  1. Build images so that the container lifecycle can be managed easily. The image should not store internal state. Data can be passed into the image at build time using command-line arguments, and Docker volumes can be used at runtime.
  2. Understand the context in which the web application runs: the project folder, a remote source, or a repository.
  3. Keep in mind that a Dockerfile can be run outside of context via standard input.
  4. Use a .dockerignore file to ensure only the necessary files and folders are included in the image. Strip out everything unnecessary at the build stage.
  5. Use multi-stage builds. This can significantly reduce the image size.
  6. Do not install what you will not use in the image.
  7. Separate applications into independent, self-contained components. This process is called decoupling.
  8. Minimize the number of layers in the image. This improves performance both during build and at runtime.
  9. If instruction parameters span multiple lines (using a line continuation character), arrange the arguments in alphabetical order. This improves readability and simplifies debugging.
  10. Use the Docker cache only for layers that will be needed to build other images. To skip the cache, add the --no-cache=true flag to the docker build command.