What are distroless images in Docker?

Key takeaways:

• Distroless images are streamlined Docker images that include only the necessary application and runtime components, omitting package managers, shells, and other standard programs, which helps minimize the size of Docker images and optimize efficiency.

• While distroless images optimize for size, they lack certain runtime dependencies and a complete operating system, meaning they are suited for specific use cases where minimalism is essential, such as running Python applications.

Minimizing the size of Docker images is crucial to enhancing the efficiency and optimization of Docker setups. One effective approach is to leverage distress images, which represent the most streamlined Linux distribution, comprising only the necessary app and runtime components. Notably, distress images exclude package managers, shells, and other typical programs found in standard Linux distributions.

Google offers distroless images for various programming languages and runtimes through GoogleContainerTools.

Key characteristics of distroless images

1. Minimalistic design: Distroless images contain only the necessary dependencies to run your application. They exclude any unnecessary software like package managers or interactive shells, which are often used for debugging or system administration tasks.

2. Reduced attack surface: Since distroless images don’t contain unnecessary components, the number of potential vulnerabilities is greatly reduced. This makes your containers more secure, as there are fewer opportunities for attackers to exploit them.

3. Smaller image size: Distroless images are typically smaller than traditional images, as they contain fewer files and libraries. This can lead to faster deployment times and reduced storage requirements.

4. No package management: Distroless images do not include package managers like apt or yum. This means that once the image is built, you cannot install new packages or modify the image from within the container. Any dependencies must be included at build time.

Why use distroless images?

There are several reasons why developers choose distroless images when containerizing their applications:

1. Security: Distroless images offer enhanced security because they include fewer tools and libraries that could be used to exploit vulnerabilities. By removing unnecessary components like shells or package managers, they reduce the attack surface, making it harder for attackers to compromise the container.

2. Efficiency: Distroless images are smaller in size, which makes them more efficient to deploy and scale. A smaller image means faster builds, reduced storage overhead, and quicker startup times.

3. Predictability: With fewer components in the image, there are fewer moving parts, making the runtime environment more predictable. This reduces the likelihood of incompatibilities or issues arising due to unnecessary software dependencies.

4. Faster CI/CD: Since distroless images are smaller, they can speed up continuous integration/continuous deployment (CI/CD) pipelines. This leads to faster testing, building, and deploying of containerized applications.

Using base image

Let’s create a Docker image with the official python:3 base image:

The size of this Docker image is 1,013,102,495 bytes, which is equivalent to 966 MB. This will result in slower downloads and higher storage costs. By using distroless images, which only include the application and necessary dependencies, we can significantly reduce the image size, improving efficiency and lowering storage requirements.

Now, we’ll see how to use distroless image to reduce the image size.

How to use distroless images

To use distroless images in Docker, you first need to choose a distroless image that suits your application’s runtime needs. Google provides several distroless images that are optimized for different types of applications, such as Python, Java, Go, Node.js, and more. Here’s an example of how to use a distroless image for a simple Python application:

The size of this docker image is 52827014 bytes, which is equivalent to 50 MB.

Types of distroless images

Google provides various distroless images for different programming languages and runtimes. Some common distroless images include:

• Python: For running Python applications with minimal dependencies.

• Java: For running Java applications without unnecessary components.

• Go: A distroless image optimized for Go applications.

• Node.js: A minimal image for running Node.js applications.

• Custom: Distroless also supports custom applications where you can use the base image for your specific needs.

Pros and cons of distroless images

The pros and cons of distroless images are:

Pros

• Smaller size: Distroless images are typically much smaller than full operating system images, leading to reduced storage and bandwidth usage.

• Increased security: By removing unnecessary tools and utilities, distroless images reduce the potential attack surface.

• Improved performance: Smaller images generally result in faster startup times and lower resource consumption.

Cons

• Limited flexibility: Distroless images are not meant to be modified after they’re built, as they don’t include package managers or shells. This can make debugging and troubleshooting more challenging.

• Build-time dependencies: All dependencies must be included during the build process, meaning you need to account for everything your application needs upfront.

When to avoid distroless images

While distroless images offer many benefits, they are not suitable for all scenarios. If you need a container for development or debugging purposes where tools like shell access or package managers are required, a distroless image may not be the best choice. In such cases, a more comprehensive base image (like Ubuntu or Alpine) might be more appropriate.

Conclusion

Based on the examples above, it becomes evident that distroless images can be employed for code optimization. However, it’s crucial to note that distroless images lack certain runtime dependencies. For instance, the distroless/python3 image doesn’t contain a complete operating system or distribution such as Debian or Alpine Linux. Instead, it exclusively includes essential components necessary for running a Python application.