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1. Concepts

A container, in one sentence

Section titled “A container, in one sentence”

A container packages an application with everything it needs (libraries, runtime, configuration) so that it runs the same way everywhere. You start it from an image, a read-only template that you download from a registry (Docker Hub, for example) or build yourself.

Term Analogy Example
Image A fixed recipe nginx, ubuntu:latest
Container A dish prepared from the recipe the web server started from nginx
Registry The recipe library docker.io
Published port The counter between Windows and the container -p 8080:80

Why you need Linux

Section titled “Why you need Linux”

Linux containers share the host machine’s Linux kernel. Windows doesn’t have one, so you need a Linux virtual machine somewhere. That is exactly what WSL 2 provides: a lightweight VM, managed by Windows, with a real Linux kernel.

Three ways to get Linux containers on Windows

Section titled “Three ways to get Linux containers on Windows”
Approach Who manages the Linux VM Tool
Docker Desktop Docker, via its own WSL distro docker-desktop docker
Podman Podman, via its WSL distro podman-machine-default podman
WSL containers WSL itself, with no third-party product wslc

What’s new: with WSL containers, the container engine is part of WSL. There is nothing else to install, and wslc.exe ships with WSL.

The two components

Section titled “The two components”
  1. The wslc.exe CLI — to build, run and inspect containers from a terminal. It follows the conventions of the Docker CLI.
  2. The WSL container API — a NuGet package (Microsoft.WSL.Containers) that lets a Windows application use Linux containers in its own logic (C#, and C++/WinRT in preview).

Key takeaways

Section titled “Key takeaways”
  • Image = template; container = running instance.
  • Linux containers need a Linux kernel → WSL 2 provides it.
  • wslc = containers built into WSL, without Docker Desktop.

Exercises

Section titled “Exercises”
  1. List the WSL distributions on your machine. Which ones belong to a container tool?
Solution
Terminal window
wsl -l -v

On my machine: docker-desktop (Docker Desktop) and podman-machine-default (Podman). These are “technical” distros managed by those tools, not distros meant to be used directly.

  1. Why can’t you run an ubuntu image directly on the Windows kernel?
Solution

A Linux image contains binaries that make Linux system calls. A container doesn’t virtualize the kernel: it shares the host’s. So you need a Linux kernel, provided here by the WSL 2 VM.