Slim Down Docker Images: Mastering Multi-Stage Builds

Unlock the Power of Efficient Dockerfiles

What is Docker?

In today’s fast-paced tech landscape, Docker has become an indispensable tool for enterprises. It enables the creation, deployment, and running of applications using containers that are independent of the operating system. A container packages the application services or functions with all necessary libraries, configuration files, dependencies, and other parts to operate. Each container shares the services of one underlying operating system.

The Importance of Docker Images

Docker Images are the set of instructions written in a file called Dockerfile. These instructions act as a multi-layered filesystem in Docker. When a Docker user runs the images, it produces one or multiple containers. Docker Images are immutable files, basically a snapshot of the container. We can make multiple containers from a single Docker image, similar to creating multiple objects instances from a single Class in object-oriented programming.

Why Reduce Docker Image Size?

Reducing Docker image size is crucial in today’s tech era, despite the relative cheapness of memory and storage. By minimizing image size, we keep only the required artifacts in the final image and remove unnecessary data. This practice:

• Follows best practices
• Reduces complexity and vulnerability in applications
• Saves time in downloading and spawning containers
• Prevents blocking of CI/CD pipelines
• Eliminates the risk of leaving keys and secrets in the Dockerfile
• Enables container immutability

Optimizing Docker Image Size

There are several ways to reduce Docker image size, including:

• Using a .dockerignore file to remove unnecessary content from the build context
• Avoiding unnecessary packages and dependencies
• Keeping layers in the image to a minimum
• Using Alpine images whenever possible
• Utilizing Multi-Stage Builds

Unlocking the Power of Multi-Stage Builds

Multi-stage builds in Docker are a game-changer. Introduced in Docker 17.05, this feature allows us to reduce image size, create better organization of Docker commands, and improve performance while keeping the Dockerfile easy to read and understand. By dividing the Dockerfile into multiple stages, we can pass the required artifact from one stage to another and deliver the final artifact in the last stage.

A Real-World Example

Let’s consider an example where we need to download a abc.tar.gz file, extract the content, and run make install. Previously, we would have to clean up every artifact before moving to the next instruction, making the Dockerfile complex and difficult to read. With multi-stage builds, we can simplify the process:

• Stage 1: Use an Ubuntu base image, update packages, install make and curl, download the abc.tar.gz file, and run make DESTDIR=/tmp install.
• Stage 2: Use an Alpine base image, copy the content from /tmp dir from Stage 1 to /abc dir, and add the path of the binary in the Entrypoint.

This approach allows us to create an optimized and reduced image without compromising the readability of the Dockerfile.

Take Your Docker Skills to the Next Level

By mastering the art of writing efficient Dockerfiles and leveraging multi-stage builds, you can take your Docker skills to new heights. Learn more about Docker and its features to stay ahead in the game.