Tutorial: Implementing Least Privilege in Docker

1. Introduction

Goal of the tutorial

This tutorial aims to guide you on how to implement the principle of least privilege in Docker. This principle ensures that Docker containers are given only the essential permissions required to perform their tasks, thereby increasing the security of applications.

What you will learn

By the end of this tutorial:
- You will understand the concept of least privilege.
- You will know how to apply the principle of least privilege in Docker.
- You will be familiar with best practices in defining permissions for Docker containers.

Prerequisites

• Basic knowledge of Docker and Docker commands.
• Docker installed on your machine.

2. Step-by-Step Guide

Understanding the Principle of Least Privilege

The principle of least privilege (PoLP) is a computer security concept in which a user or program is given the minimum levels of access or permissions needed to perform its duties. In context of Docker, this means running containers with minimal permissions.

Applying the Principle of Least Privilege in Docker

By default, Docker containers are run as root. However, this presents a security risk because if the container is compromised, the attacker could gain root access to the Docker host. To avoid this, we can run containers as a non-root user.

Best Practices and tips

• Always specify a user in the Dockerfile. This can be done using the USER directive. If you do not specify a user, the container will run as root.
• Use the --user flag when running docker commands to specify the user.

3. Code Examples

Example 1: Specifying a User in the Dockerfile

# Start from a base image
FROM ubuntu:latest

# Create a new user
RUN useradd -ms /bin/bash myuser

# Specify the user
USER myuser

In this Dockerfile, we start from the ubuntu:latest base image, create a new user named myuser, and then specify that the container should be run as myuser.

Example 2: Using the --user flag

docker run -d --user 1001 myimage

In this example, we run the container as the user with the UID 1001.

4. Summary

In this tutorial, you have learned about the principle of least privilege and how to apply it in Docker. You've learned that by default, Docker containers run as root, and how you can run containers as non-root users to increase security.

Next Steps

Continue learning about Docker security by exploring other topics such as Docker Secrets, Docker Content Trust, and Network Policies in Kubernetes for Docker.

Additional Resources

1. Docker Security Best Practices
2. Docker and the Principle of Least Privilege

5. Practice Exercises

1. Exercise 1: Write a Dockerfile that starts from the alpine:latest base image and specifies a non-root user.
2. Solution:
   ```Dockerfile
   # Start from the alpine:latest base image
   FROM alpine:latest

# Add a new user
RUN adduser -D myuser

# Specify the user
USER myuser
`` This Dockerfile creates a new usermyuserand specifies that the container should be run asmyuser`.

1. Exercise 2: Run a Docker container as a user with UID 1234.
2. Solution:
   bash docker run -d --user 1234 myimage
   This command will run the Docker container as the user with the UID 1234.

Tips for Further Practice

Explore how to run containers as a non-root user in different base images, like debian, centos, etc. Each Linux distribution has different commands to add users, so this will give you a broader understanding.