Why Switch from Docker to containerd? A Quick Guide for Kubernetes Users

containerd Introduction

containerd is an industrial‑grade container runtime that emphasizes simplicity, robustness and portability. It manages the full container lifecycle on the host, including image transfer and storage, execution, management, storage and networking.

Docker vs containerd

containerd was split out from Docker and can serve as a low‑level runtime; it is now the preferred runtime for Kubernetes.

Many cloud platforms also support containerd as the underlying runtime.

K8s CRI

Kubernetes defines the Container Runtime Interface (CRI) so any runtime that implements CRI can be used as the underlying runtime.

Why does K8s abandon Docker for containerd?

If Docker is used, kubelet must go through

dockershim

to call Docker, which then calls containerd.

If containerd is used, its built‑in

CRI

plugin allows kubelet to call containerd directly.

Using containerd improves performance (shorter call chain) and reduces resource consumption because Docker includes many extra features.

Using containerd

If you have used Docker, you can learn containerd in about five minutes.

In a previous article we installed K3s, which uses containerd by default; installing K3s gives you containerd.

Simply replace Docker commands with

crictl

to operate containerd, e.g., list running containers.

<code>crictl ps</code>

<code>CONTAINER   IMAGE   CREATED   STATE   NAME   ATTEMPT   POD ID
4ca73ded41bb6   3b0b04aa3473f   Less than a second ago   Running   helm   20   21103f0058872
3bb5767a81954   296a6d5035e2d   About a minute ago   Running   coredns   1   af887263bd869
a5e34c24be371   0346349a1a640   About a minute ago   Running   nginx   1   89defc6008501</code>

List all images:

<code>crictl images</code>

<code>IMAGE                                 TAG   IMAGE ID   SIZE
docker.io/library/nginx               1.10 0346349a1a640 71.4MB
docker.io/rancher/coredns-coredns   1.8.0 296a6d5035e2d 12.9MB
docker.io/rancher/klipper-helm      v0.4.3 3b0b04aa3473f 50.7MB
docker.io/rancher/local-path-provisioner v0.0.14 e422121c9c5f9 13.4MB
docker.io/rancher/metrics-server   v0.3.6 9dd718864ce61 10.5MB
docker.io/rancher/pause            3.1 da86e6ba6ca19 327kB</code>

Enter a container’s shell (use container ID):

<code>crictl exec -it a5e34c24be371 /bin/bash</code>

Check resource usage, which is very low:

<code>crictl stats</code>

<code>CONTAINER   CPU %   MEM   DISK   INODES
3bb5767a81954 0.54 14.27MB 254B 14
a5e34c24be371 0.00 2.441MB 339B 16</code>

Conclusion

Switching from Docker to containerd is straightforward; just replace Docker commands with

crictl

. Because both are from the same company, the usage is similar, so the deprecation of Docker in Kubernetes has little impact for developers.