When using Docker, one of the main goals is to create container images that are as compact, secure, and high-performance as possible. This is particularly crucial in production environments, cloud infrastructures, and serverless architectures, where every megabyte counts.
One tool that helps achieve this is docker-slim.
In this article, we’ll explain what docker-slim is, how it works, and why you should add it to your DevOps toolbox.
Why Minimize Docker Images?
The standard Dockerfile-based approach often results in bloated images containing:
- Unused runtime dependencies (compilers, test utilities)
- Debugging tools
- Temporary files
- Packages installed “just in case”
This leads to:
- Slower build and delivery times
- Larger attack surface (more tools = more vulnerabilities)
- Increased storage and network costs
What Does docker-slim Do?
docker-slim is a CLI tool that analyzes how your container behaves during runtime and builds a minimally required Docker image by removing everything unnecessary.
It works by:
- Launching your container in “inspection” mode
- Monitoring which files and libraries the application actually uses
- Creating a new, optimized image that includes only those files
Benefits
- Security — Fewer potential vulnerabilities
- Size — Images can shrink by 10–30x
- Simplicity — No need to manually fine-tune base images
- Compatibility — Works with most languages (Python, Node.js, Go, Java, etc.)
How to Use docker-slim
Example for a Python app:
docker build -t myapp .
docker-slim build myappResult:
- Original image: myapp
- Optimized image: myapp.slim
Example output:
docker images
REPOSITORY TAG IMAGE ID SIZE
myapp latest abc123 350MB
myapp.slim latest def456 18MB
Advanced Features
- http-probe — Automatically generates HTTP requests to trigger all app routes
- user-probes — Define custom probes (scripts, curl, etc.)
- CI/CD integration — Easily use with GitHub Actions, GitLab CI, and more
- Security analysis — Highlights risks and dependency issues
Limitations
- The app must actually run in inspection mode
- Dynamic dependencies may be missed if not triggered during analysis (can be resolved with custom probes)
- Not ideal for apps with heavy initialization or GUI/headless UIs
Summing up
docker-slim is an efficient and user-friendly tool designed to automate the optimization of Docker images. It significantly reduces image size, boosts security, and speeds up deployments — all without requiring manual Dockerfile rewrites. It’s especially valuable in production, microservices, cloud, and CI/CD environments.
If you’re not using docker-slim yet, now is a great time to try it. It’s a small step that can make a huge difference in the quality and efficiency of your infrastructure.
Serverspace Glossary
The Serverspace Glossary is an invaluable resource for users diving into the world of cloud computing, server management, and DevOps. It serves as a comprehensive guide, providing clear and concise definitions for essential terms and concepts that are frequently encountered within cloud technology, IT infrastructure, and the broader tech industry. This glossary is ideal for a wide range of users, from beginners just starting with cloud solutions to seasoned professionals looking to refresh or expand their knowledge.
Covering an extensive range of topics, the glossary includes key terms related to server virtualization, networking, storage solutions, security protocols, containers, and cloud-native technologies. Each entry is carefully crafted to help users quickly grasp complex technical terminology, ensuring they can navigate through technical documentation, guides, and tutorials with ease. Additionally, the glossary simplifies advanced concepts, making them accessible to individuals without a deep technical background, while also providing value to those looking for more detailed insights.
