Security Best Practices for Docker Images

Minimize the Attack Surface

• Use a minimal base image. The base image is the foundation of your Docker image. Choose a minimal base image that only contains the necessary packages and dependencies. This reduces the attack surface by minimizing the number of potential vulnerabilities. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-a-minimal-base-image
  • Example: Instead of using a full-featured operating system like Ubuntu, use a minimal image like alpine or debian:slim.
• Avoid installing unnecessary packages. Only install the packages that are absolutely necessary for your application. This reduces the number of potential vulnerabilities and keeps your image size small. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-a-minimal-base-image
  • Example: If your application only needs to run a web server, only install the web server packages and its dependencies.
• Run as a non-root user. Running your application as a non-root user limits the damage that can be done if your image is compromised. This is a critical security best practice. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#avoid-running-as-root
  • Example: Use the USER instruction in your Dockerfile to create a non-root user and switch to it.
• Use a dedicated user for the application. Create a dedicated user for your application instead of using a shared user. This helps to isolate your application and prevent other applications from accessing its resources.
  • Example: Create a user called myapp with only the necessary permissions.
• Avoid running as the root user. Running as root grants the application full system access, which is unnecessary and increases the risk of exploitation. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#avoid-running-as-root
  • Example: In your Dockerfile, use USER to specify a non-root user.

Protect Sensitive Information

• Do not store secrets directly in the image. This makes your secrets vulnerable to attacks. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#avoid-hardcoding-secrets
  • Example: Use environment variables or secrets management solutions to store secrets securely.
• Avoid storing sensitive data in your image. If you must store sensitive data, encrypt it before storing it in the image. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#avoid-storing-sensitive-data
  • Example: Use openssl to encrypt sensitive data before including it in the image.
• Use Docker secrets to store sensitive information. Secrets are encrypted and stored separately from the image, making them more secure. https://docs.docker.com/engine/reference/commandline/secret_create/
  • Example: Use the docker secret create command to create a secret and then reference it in your application using environment variables.

Secure the Image Building Process

• Use multi-stage builds. Multi-stage builds help you to create smaller, more secure images by separating the build process from the runtime environment. https://docs.docker.com/develop/develop-images/multistage-build/
  • Example: Use a separate stage for building your application and a separate stage for running it.
• Avoid running as root during the build process. This reduces the risk of vulnerabilities being introduced during the build process. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#avoid-running-as-root
  • Example: Use the USER instruction in your Dockerfile to specify a non-root user for the build process.
• Use a secure CI/CD pipeline. Your CI/CD pipeline should include security checks to ensure that your images are built securely. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#secure-the-image-building-process
  • Example: Include vulnerability scanning tools like Snyk or Trivy in your CI/CD pipeline.
• Sign your images. Signing your images ensures that they haven’t been tampered with. https://docs.docker.com/engine/reference/commandline/image_sign/
  • Example: Use the docker image sign command to sign your images.

Secure the Image Distribution Process

• Store images in a secure registry. Use a secure registry to store your images and control access to them. https://docs.docker.com/registry/
  • Example: Use Docker Hub, a private registry, or a self-hosted registry.
• Use a secure transport protocol. Ensure that you are using a secure transport protocol, such as HTTPS, to transfer your images. https://docs.docker.com/registry/
  • Example: Configure your registry to use HTTPS.

Other Best Practices

• Scan images for vulnerabilities. Use vulnerability scanning tools to identify and fix security vulnerabilities in your images. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-vulnerability-scanners
  • Example: Use Snyk, Trivy, or Aqua Security.
• Keep your images up to date. Update your images regularly to patch vulnerabilities. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#keep-your-images-up-to-date
  • Example: Use the docker pull command to get the latest version of your images.
• Use a security policy scanner. Use a security policy scanner to ensure that your images meet your security policies. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-a-security-policy-scanner
  • Example: Use Open Policy Agent or Anchore.
• Use an immutable image registry. An immutable image registry prevents unauthorized changes to your images. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-an-immutable-image-registry
  • Example: Use a registry like Harbor or JFrog Xray.
• Use a Docker image analysis tool. A Docker image analysis tool can help you to understand the contents of your images and identify potential security risks. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-a-docker-image-analysis-tool
  • Example: Use Clair or Anchore.
• Monitor your Docker containers. Monitor your containers for suspicious activity, such as unusual resource usage or network connections. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#monitor-your-docker-containers
  • Example: Use tools like Prometheus or Grafana.
• Use a security hardening guide. A security hardening guide provides recommendations for securing your images and containers. https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#use-a-security-hardening-guide
  • Example: Use the Docker Security Best Practices guide: https://docs.docker.com/develop/develop-images/dockerfile_best-practices/

By following these best practices, you can build and deploy secure Docker images that protect your applications and data.