Dockerfile Best Practices

Introduction

A Dockerfile is a text document that contains the instructions for building a Docker image. To write a Dockerfile, create a new file called "Dockerfile" (without any extension) and enter the instructions in the file.

Here is a simple example of a Dockerfile that creates an image based on the Ubuntu operating system and installs the Apache web server:

# Use the Ubuntu base image
                                    FROM ubuntu:20.04
                                    # Update the package manager and install Apache
                                    RUN apt-get update && apt-get install -y apache2
                                    # Expose the default Apache port
                                    EXPOSE 80
                                    # Run Apache in the foreground
                                    CMD ["/usr/sbin/apache2ctl", "-D", "FOREGROUND"]

In this example, the FROM instruction specifies the base image to use, the RUN instruction installs the Apache web server, the EXPOSE instruction tells Docker to expose port 80, and the CMD instruction tells Docker to run Apache in the foreground.

To build a Docker image from this Dockerfile, use the docker build command:

docker build -t my-apache-image .

Best Practices for Dockerfile

1. Use a Minimal Base Image

Start your Dockerfile with a minimal base image, such as a Linux distribution's official "slim" or "alpine" image. This will help keep your image small and reduce the attack surface.

2. Use Multi-Stage Builds

Use multi-stage builds to separate the build environment from the runtime environment. This will allow you to keep the build tools and dependencies out of the final image, reducing its size and improving its security.

3. Use the .dockerignore File

Use a .dockerignore file to exclude files and directories that don't need to be included in the image. This will help keep your image small and reduce the build time.

4. Use COPY Instead of ADD

Use the COPY instruction instead of the ADD instruction to copy files and directories into the image. Unlike ADD, COPY does not automatically extract archives or download files from the internet, which can help prevent security issues.

5. Use RUN to Install Packages

Use the RUN instruction to install packages and dependencies in your Dockerfile. This will help ensure that the packages and dependencies are installed in a consistent and reproducible way.

6. Use Labels

Use labels to add metadata to your Docker images, such as the maintainer's name and contact information, the version number, and the application's name and description. This will make it easier to manage and organize your images.

Contact us to apply best practices to your Dockerfiles!