Building a Home-Grown Docker System

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.
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