Skip to main content

Containers vs. VMs: The Foundation

Key Takeaways for AI & Readers
  • OS Virtualization: Containers share the host kernel but isolate user space, making them lighter than VMs.
  • Image vs. Container: Images are read-only blueprints; containers are their live, executable instances.
  • Registry: Centralized storage for images (e.g., Docker Hub) used to distribute applications.
  • Runtime: The underlying engine (like containerd) that executes containers on a host.

Before diving into Kubernetes, you must understand the atom it manages: the Container.

What is a Container?​

A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.

Containers vs Virtual Machines (VMs)​

App ABins/Libs
App BBins/Libs
App CBins/Libs
Guest OS
Guest OS
Guest OS
Hypervisor
Host Operating System
Infrastructure (Hardware)
Each App has its own Operating System. Heavy, slow to boot, excellent isolation.
  • VMs: Virtualize the hardware. Each VM has a full OS (Kernel + User Space) running on top of a Hypervisor. They are heavy and slow to boot (minutes).
  • Containers: Virtualize the Operating System. All containers share the host's Linux Kernel but have their own isolated User Space (bins/libs). They are lightweight and boot instantly (milliseconds).

Key Concepts​

1. Image​

The blueprint. A read-only template with instructions for creating a Docker container.

  • Example: nginx:latest, node:18-alpine
  • Built using a Dockerfile.

2. Container​

The running instance of an image. You can have many containers running from the same image.

3. Registry​

The library. A place to store and download images.

  • Public: Docker Hub, Quay.io.
  • Private: AWS ECR, Google Artifact Registry.

4. Runtime​

The engine. The software that actually runs the containers on the host machine.

  • Docker: The most famous one.
  • containerd: The industry standard runtime (used by modern Kubernetes).
  • CRI-O: Another lightweight runtime for K8s.

The Kubernetes Connection​

Kubernetes doesn't build your source code. It doesn't even build your container images.

  1. You build your image.
  2. Push it to a Registry.
  3. Tell Kubernetes: "Run 3 copies of this image".