What is Containerization?

• A lightweight alternative to full machine virtualization.
• Containers package applications and dependencies into a single unit.
• Isolated from the host system but share the host OS kernel.
• Common tools: Docker, Kubernetes, LXC.

Why Build Your Own Docker?

• Learn the fundamentals behind container technology.
• Gain flexibility for custom container use cases.
• Explore low-level Linux tools like namespaces and cgroups.
• Understand how containers achieve isolation and resource control.

Key Concepts Behind Docker

• Namespaces: Isolates the container’s view of system resources (e.g., PID, mount points).
• Control Groups (cgroups): Limits and tracks resource usage (CPU, memory, I/O).
• UnionFS: Layered file system used to build container images.
• Container Daemon: Manages and runs containers.

Essential Tools to Build a Container

• chroot: Changes the root directory for a process.
• unshare: Creates new namespaces for isolation.
• cgroups: Controls resource limits for processes.
• mount: Mounts directories and file systems within containers.

Step 1 – Setting Up Namespaces

• Use the unshare command to create process isolation.
• Separate the container’s view of the filesystem and network.
• Isolate the process’s PID, so it doesn’t interfere with host processes.

Step 2 – Implementing Resource Control with cgroups

• Set memory, CPU, and I/O limits using cgroups.
• Example: Create a cgroup to limit a process’s memory usage.
• Control resource allocation for better efficiency and performance.

Step 3 – File System Layers

• Implement UnionFS or similar layered file system technology.
• Stack multiple layers to build the container’s root file system.
• Ensure file system changes are kept separate from the base image.

Step 4 – Running the Container

• Combine the previously implemented namespaces and cgroups.
• Mount the necessary file systems and prepare the container’s environment.
• Launch the containerized process inside the isolated environment.

Conclusion & Next Steps

• Home-grown Docker provides insight into how containers work.
• Explore building your own container management system.
• Learn advanced topics like networking containers and orchestration.
• Next steps: Explore Kubernetes, advanced Docker features, and container security.