Containerization has radically simplified the process of delivering, scaling, and maintaining applications, becoming the de facto standard in DevOps practices. However, along with this convenience came new challenges. One of them is inefficient Docker images. Poorly built containers often become excessively “heavy,” resulting in slower CI/CD processes, excessive disk and memory usage — and in some cases, critical vulnerabilities. Optimizing Docker images is an essential step for production environments. Below are practical recommendations to help you create lightweight, fast, and secure containers — without unnecessary pain.
What is Containerization and How It Works?
Containerization is a modern method of packaging and running applications in self-contained units known as containers. These containers bundle everything an app needs to function — including code, runtime, libraries, and system tools — into a portable and consistent environment. Unlike traditional virtual machines, containers run on a shared OS kernel, which makes them much more lightweight and quicker to launch.
Containers are widely used for a variety of purposes, such as:
- Consistent development and production environments
- Microservices deployment and orchestration
- Efficient CI/CD pipelines
- Scalable cloud-native applications
- Isolation for testing and debugging
- Rapid prototyping and development cycles
By using containerization, teams can streamline application delivery, reduce configuration drift, and increase infrastructure efficiency across all stages of the software lifecycle.
1. Use Multi-Stage Builds
Multi-stage builds offer a highly efficient strategy for streamlining Docker images. By dividing the build and runtime environments into distinct stages, you can compile, test, and prepare your application in a controlled build phase, then export only the critical components—like executables or static files—into a lean, production-ready container. This approach not only minimizes the final image size but also strips away unnecessary dependencies and temporary artifacts, resulting in cleaner, more secure, and easier-to-manage deployments.
Example with Go:
FROM golang:1.22 AS builder
WORKDIR /app
COPY . .
RUN go build -o app
# Minimal production image
FROM alpine:latest
WORKDIR /app
COPY --from=builder /app/app .
CMD ["./app"]
Advantages:
- The final image contains only the binary and what's needed to run it.
- No compilers, extra libraries, or temporary files.
2. Choose Minimal Base Images
The smaller the base image, the lighter and more secure the final container will be.
Recommendations:
- Use alpine instead of ubuntu or debian if your app doesn’t rely on glibc.
- Try Google’s Distroless images — they contain only what's necessary to run the app, with no shell or extra packages.
Example:
COPY app /
CMD ["/app"]
3. Order Dockerfile Instructions to Maximize Caching
Docker caches layers. If your code changes frequently, you can save build time by ordering commands correctly.
Good structure:
RUN go mod download
COPY . .
RUN go build -o app
This way, dependency downloads are reused if go.mod remains unchanged.
4. Remove Temporary Dependencies and Junk
Many packages are only needed during the build stage. Remove them to avoid carrying them into the final image.
Example:
apt-get install -y build-essential && \
make build && \
apt-get purge -y build-essential && \
apt-get autoremove -y && \
apt-get clean && \
rm -rf /var/lib/apt/lists/*
This can eliminate dozens of megabytes of unnecessary data.
5. Use Automatic Compression with docker-slim
docker-slim analyzes your image and removes everything that isn’t essential.
Example:
The result is a much lighter image, without sacrificing functionality.
Recommendations and Anti-Patterns
- Keep images compact — ideally under 100 MB.
- Don’t add packages “just in case” — every MB affects deployment speed.
- Scan image security with trivy:
- Never hardcode secrets into images — use environment variables and secret managers.
General Tips
- Use .dockerignore to avoid copying unnecessary files (.git, node_modules, logs, etc.).
- Minimize the number of RUN commands by combining them to reduce layers.
- Automate image building and validation via CI/CD (e.g., GitHub Actions, GitLab CI).
By following these best practices, you’ll not only streamline and accelerate the entire container build and delivery pipeline, but also achieve a substantial reduction in image size — a critical factor in cloud-native and clustered environments where efficiency and scalability are key. Leaner images translate to faster pull times across nodes, lower storage consumption, and decreased network bandwidth usage, which is especially beneficial in CI/CD pipelines and edge deployments. In addition, smaller images tend to load faster and reduce the startup time of services, contributing to improved system responsiveness. Just as importantly, by eliminating unnecessary packages, tools, and libraries, and relying on minimal, purpose-built base images, you effectively shrink the container's attack surface. This significantly lowers the risk of vulnerabilities, simplifies compliance efforts, and makes security audits more manageable. Ultimately, optimized images lead to more predictable, secure, and cost-effective production environments.
Docker and Serverspace
Looking to simplify your CI/CD pipeline and gain instant access to a reliable, scalable infrastructure? Serverspace makes it easy. With just a few clicks, you can deploy high-performance virtual machines in minutes — no complex setup, no delays. Its powerful API enables full automation of application delivery, making it ideal for fast-paced DevOps workflows. As your project grows, Serverspace scales with you, letting you adapt resources in real time to meet changing demand. Whether you're launching a new application, running development and staging environments, or migrating legacy systems to the cloud, Serverspace provides the flexibility, control, and security you need at every step. Thanks to its intuitive interface and rich Cloud Marketplace, you can instantly spin up pre-configured environments with tools like Docker, Kubernetes, GitLab, and more. Developers can focus on shipping code, not managing servers. Supercharge your CI/CD pipelines with Serverspace and bring agility, speed, and reliability to your DevOps operations.