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The Dockerfile

Writing build instructions for custom images

Building Custom Images

A Dockerfile is a text file with instructions for building a Docker image. Each instruction creates a new layer in the image.

Simple Dockerfile


  # Use Node.js 20 as the base image
  FROM node:20

  # Set working directory inside the container
  WORKDIR /app

  # Copy package.json and install dependencies
  COPY package*.json ./
  RUN npm install

  # Copy the rest of your application code
  COPY . .

  # Expose port 3000
  EXPOSE 3000

  # Start the application
  CMD ["node", "server.js"]

Dockerfile Instructions

Building the Image

 5d17c0f5e3c2
  Step 2/6 : WORKDIR /app
   ---> Using cache
   ---> 7e1c8d3f9a4b
  ...
  Successfully built 9f2e1d4c8a7b
  Successfully tagged myapp:1.0

🧪 Quick Quiz

What is a Dockerfile?