Docker Container Security: Best Practices

1. Introduction

1.1 Tutorial's goal

This tutorial aims to provide an understanding of best practices for Docker container security. We will focus on areas such as image security, container isolation, and network settings.

1.2 What the user will learn

• How to secure Docker images
• Best practices for isolating containers
• Techniques to secure network settings
• Using Docker security scan tools

1.3 Prerequisites

• Basic knowledge of Docker
• Docker installed on your system

2. Step-by-Step Guide

2.1 Image Security

Docker images are the foundation of your containers. Ensuring these images are secure is crucial. Here are some best practices:
- Always use official images or trusted sources.
- Regularly update images to receive security patches.
- Minimize the use of third-party software or libraries, which may contain vulnerabilities.

# Example of pulling an official image
docker pull ubuntu:latest

2.2 Container Isolation

Isolation is a fundamental part of Docker container security. Docker provides various features like namespaces, control groups (cgroups), and seccomp profiles to help with this.

• Use user namespaces to separate container and host user IDs, preventing a container from getting host user permissions.
• Limit resources with cgroups to prevent a single container from consuming all system resources.
• Use seccomp profiles to restrict the system calls a container can make.

# Example of running a container with limited resources
docker run -it --cpus=".5" --memory="100m" ubuntu:latest

2.3 Secure Network Settings

Docker's default network settings might not always be secure. Here are some tips:

• Use network namespaces to isolate container network interfaces.
• Avoid exposing unnecessary ports to limit attack surface.
• Use firewall rules to restrict network access.

# Example of running a container with a specific exposed port
docker run -it -p 8080:80 nginx:latest

3. Code Examples

Here are some practical examples of secure Docker usage.

3.1 Using Docker Bench for Security

Docker Bench for Security is a script that checks for common best-practices around deploying Docker containers in production.

# Running Docker Bench for Security
docker run -it --net host --pid host --userns host --cap-add audit_control \
    -e DOCKER_CONTENT_TRUST=$DOCKER_CONTENT_TRUST \
    -v /var/lib:/var/lib \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -v /usr/lib/systemd:/usr/lib/systemd \
    -v /etc:/etc --label docker_bench_security \
    docker/docker-bench-security

This script will output a report with all the checks passed, skipped, and warnings.

3.2 Using Docker Content Trust

Docker Content Trust (DCT) provides the ability to use digital signatures for data sent to and received from remote Docker registries.

# Enable Docker Content Trust
export DOCKER_CONTENT_TRUST=1

After enabling DCT, all operations using Docker images will be verified for authenticity.

4. Summary

We've learned to secure Docker images, isolate containers, and secure network settings. We also reviewed using Docker Bench for Security and Docker Content Trust.

Continue learning by exploring other Docker security features such as Docker Secrets, Docker Swarm, and Kubernetes.

Here are some resources to help further your understanding:
- Docker Security Best Practices
- Docker Bench for Security on GitHub

5. Practice Exercises

1. Run a Docker container with limited memory and CPU resources.
2. Enable Docker Content Trust and try pulling an image.
3. Use Docker Bench for Security and analyze the report.

5.1 Solutions

1. docker run -it --cpus=".5" --memory="100m" ubuntu:latest
2. export DOCKER_CONTENT_TRUST=1 and then docker pull ubuntu:latest
3. Refer to the code example in section 3.1.

Keep practicing by trying to secure your Docker containers using all the techniques we've discussed. Happy Docker-ing!