Distroless Docker Images: A Lightweight and Secure Solution for Docker Containers

Docker is a powerful tool for creating, shipping and running applications in containers. Docker images are typically based on Linux distributions, like Debian, Ubuntu, or Alpine. These distributions provide the basics required to run your application, but they also contain a lot of extra packages that aren't necessary. This excess baggage can increase both the size and security risks of your Docker images.

That's why Google created the concept of distroless Docker images. Distroless images are containers that only contain the application and its runtime dependencies, without any operating system-specific software or libraries. This approach reduces the attack surface and makes the image much smaller, lighter in weight, and more secure.

What are distroless Docker images?

Distroless Docker images contain just the minimal dependencies required to run an application. They don't include extraneous software, configuration files, or operating system packages. The result is a lightweight, highly secure container that can only run your specific application, with much lower risks of an attack.

Distroless images are based on images that use scratch as the base image, which means there are no Linux distributions or libraries present. And because the image has no operating system, it's impossible to install additional packages, making it highly secure.

Advantages of distroless Docker images

Distroless Docker images provide a number of advantages when compared to normal Docker images based on full Linux distributions:

Enhanced security

One of the main advantages of distroless images is enhanced security. By reducing the surface of the image, fewer potential attack vectors are available for malicious actors. Distroless images do not include any system libraries or shells, making them less susceptible to CVEs related to OS packages.

Reduced footprint

Distroless images are significantly smaller than traditional Docker images because they don’t include an entire OS distribution to run the application. A smaller image size means a reduced attack surface, faster deployment, and lower storage requirements.

Simple and predictable behavior

Distroless images only include the application and its dependencies, so their behavior is much simpler and more predictable. This significantly reduces the number of variables in the environment, keeping the environment consistent across deployments.

Optimized for microservices

Distroless images are ideal for microservices architecture because they're lightweight, have a small attack surface, and provide the required resources for the application to run without additional dependencies.

How to use distroless Docker images

Distroless Docker images are relatively easy to use. Google provides base images for several popular languages and runtimes, as well as support for customizing the images.

To create a distroless Docker image, start with the appropriate base image for your application. Then, include only the necessary files and libraries required to run your application in the container, using the appropriate Dockerfile commands.

Here's an example of a minimal Dockerfile that builds a distroless Docker image for a simple Go web server:

# Use the distroless base image for Go
FROM gcr.io/distroless/base-debian10

# Copy the Go binary to the container
COPY server /

# Set the command to run on container start
CMD ["/server"]

Note that the build process in this case must include statically linking any necessary dependencies so that they're baked into the built binary.

Conclusion

Distroless Docker images are an excellent way to improve the security and efficiency of your Docker containers. By eliminating unnecessary software and packages, these images are highly secure, faster, and lightweight. While distroless images require some additional work to build and configure, the benefits, especially for microservices-based applications, outweigh the effort.

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