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Container Runtimes: How Containers Work

Container runtimes run containers. containerd. runc. They're the foundation of Docker.

Here's the thing: Understanding runtimes helps you understand Docker. Kubernetes. Modern deployment.

What Container Runtimes Do​

Container runtimes:

  • Run containers
  • Manage container lifecycle
  • Isolate containers
  • Provide the foundation

My take: Runtimes are the engine. Docker uses them. Kubernetes uses them.

containerd: Container Runtime​

What containerd Is​

containerd is a container runtime. Docker uses it. Kubernetes uses it.

My take: containerd is the runtime. It runs containers.

containerd Commands​

# List containers
ctr containers list

# Run container
ctr run docker.io/library/nginx:latest nginx

# List images
ctr images list

My take: ctr is containerd's CLI. Use it to manage containers.

runc: Low-Level Runtime​

What runc Is​

runc is the low-level runtime. It actually runs containers.

My take: runc is the actual runner. containerd uses it.

Docker Connection​

Key point: Docker uses containerd and runc:

  • Docker = High-level interface
  • containerd = Container runtime
  • runc = Low-level runner

My take: Understanding runtimes = understanding Docker. Learn them.

Container Fundamentals​

Namespaces​

Containers use Linux namespaces:

  • PID namespace
  • Network namespace
  • Mount namespace
  • User namespace

My take: Namespaces provide isolation. Containers use them.

cgroups​

cgroups limit resources:

  • CPU limits
  • Memory limits
  • I/O limits

My take: cgroups limit resources. Containers use them.

When You'll Use Runtimes​

You'll use runtimes when:

  • Understanding Docker
  • Understanding Kubernetes
  • Debugging containers
  • Building container tools

Most of the time: You'll use Docker. But understanding runtimes helps.

My take: Learn runtimes to understand containers. But use Docker for daily work.

Common Mistakes (I've Made These)​

  1. Too complex for beginners: Start with Docker. Learn runtimes later.

  2. Not understanding layers: Runtimes are layers. Understand them.

  3. Mixing concepts: Docker, containerd, runc are different. Understand each.

  4. Not using Docker: Docker is easier. Use it for daily work.

  5. Overthinking: Containers are simple. Don't overthink them.

Real-World Examples​

List Containers​

ctr containers list

Run Container​

ctr run docker.io/library/nginx:latest nginx

What's Next?​

Now that you understand runtimes, you understand containers. Or learn about Cloud Integration for cloud platforms.

Personal note: Runtimes seemed complex at first. Then I learned them. Now I understand Docker better. Learn runtimes. Understand containers.