Kubernetes `RuntimeHandler "runc" not supported` when creating container - docker

Question

I was trying to specify the runtime of containers deployed using Kubernetes. I follow the guide in this link and creating the following RuntimeClass:
apiVersion: node.k8s.io/v1beta1
kind: RuntimeClass
metadata:
name: runc
handler: runc
# $ kubeclt get RuntimeClass
# NAME HANDLER AGE
# runc runc 59m
Then, I set my Pod spec.runtimeClassName="runc". However, when deploying this using Kubernetes, I got the following error:
Warning FailedCreatePodSandBox 2m43s (x141 over 32m) kubelet, jetson1 Failed to create pod sandbox: rpc error: code = Unknown desc = RuntimeHandler "runc" not supported
I can run the container with docker and --runtime=runc without any error. But when deploying it with K8s, the error occur. The following is my docker info:
Client:
Debug Mode: false
Server:
Containers: 11
Running: 5
Paused: 0
Stopped: 6
Images: 12
Server Version: 19.03.6
Storage Driver: overlay2
Backing Filesystem: extfs
Supports d_type: true
Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: bridge host ipvlan macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: nvidia runc
Default Runtime: nvidia
Init Binary: docker-init
containerd version:
runc version:
init version:
Security Options:
seccomp
Profile: default
Kernel Version: 4.9.140-tegra
Operating System: Ubuntu 18.04.4 LTS
OSType: linux
Architecture: aarch64
CPUs: 4
Total Memory: 3.871GiB
Name: jetson1
ID: HLZ4:DQKM:J7YY:OMDN:JXXZ:PFL5:YJGT:DJBM:SMSL:UTZA:WCZ4:GUD4
Docker Root Dir: /var/lib/docker
Debug Mode: false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: false
Any suggestions will be appreciated. Thank you!

Answer 1

While runc is able to create containers, it's a rather low-level component. Most tools we know as container runtimes actually rely on it in some way. This answer to another question gives a great overview of it.
The RuntimeClass feature in Kubernetes to target a specific conainer runtime requires it to implement the CRI (Container Runtime Interface) on the local nodes (the "Setup" part of your shared link briefly talks about it). I did some quick research and there is no hint that runc is implementing CRI directly. If it was, Kubernetes would skip accessing Docker as you did; it would use that interface to talk to another component directly from kubelet. Checking Docker settings therefore doesn't help to see if runc is a viable Kubernetes container runtime.
So, you should review why you're trying to do this - runc is likely already used in your default container rumtime stack without you maybe realizing it. Kubernetes has documentation for alternative container runtimes, you can look into installing these if you are looking for something more lightweight than Docker.