Dockerfile Creation

A Dockerfile is a text file that contains instructions for building a Docker image. It’s like a recipe: it specifies the base operating system, dependencies, commands to execute, and the application code to include. Docker uses the Dockerfile to automate the image creation process.

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Dockerfile Instructions

Here are some of the most common Dockerfile instructions:

FROM

• Description: Specifies the base image for your new image. Every Dockerfile must start with a FROM instruction.

• Example:

  FROM ubuntu:22.04  # Use the official Ubuntu 22.04 image as the base
  FROM python:3.9-slim # Use a slim Python 3.9 image
  FROM scratch       # Create an empty image
  

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WORKDIR

• Description: Sets the working directory inside the image. Subsequent RUN, COPY, ADD, CMD, and ENTRYPOINT instructions will be executed in this directory. It’s like using cd in a shell script. If the directory doesn’t exist, it will be created.

• Example:

  WORKDIR /app  # Set the working directory to /app
  

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COPY

• Description: Copies files and directories from the host machine (where you’re running docker build) into the image.

• Example:

  COPY requirements.txt /app/  # Copy requirements.txt to the /app directory in the image
  COPY src/ /app/src/         # Copy the entire 'src' directory to /app/src/
  COPY . /app                # Copy everything from the current directory to /app (be careful with this!)
  

  Note: It’s best practice to be specific about what you copy. Copying everything (COPY . /app) can lead to larger image sizes and potential security issues if you accidentally include sensitive files. Use a .dockerignore file (similar to .gitignore) to exclude files and directories from the build context.

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ADD

• Description: Similar to COPY, but with additional features:
  • Can copy files from URLs.
  • Can automatically extract compressed archives (tar, gzip, bzip2, etc.).
• Example:

  ADD [https://example.com/my_app.tar.gz](https://www.google.com/search?q=https://example.com/my_app.tar.gz) /tmp/
  

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