What is Kubernetes RuntimeClass?

Question

Accepted Answer

**RuntimeClass** — select container runtime for Pod scheduling.

```yaml
apiVersion: node.k8s.io/v1
kind: RuntimeClass
metadata:
  name: gvisor
handler: gvisor
scheduling:
  nodeSelector:
    node.kubernetes.io/runtime: gvisor
---
apiVersion: node.k8s.io/v1
kind: RuntimeClass
metadata:
  name: kata
handler: kata
overhead:
  podFixed:
    memory: "160Mi"
    cpu: "250m"
---
apiVersion: node.k8s.io/v1
kind: RuntimeClass
metadata:
  name: nvidia
handler: nvidia
scheduling:
  nodeSelector:
    nvidia.com/gpu.present: "true"
---
# Pod using RuntimeClass
apiVersion: v1
kind: Pod
metadata:
  name: sandboxed-pod
spec:
  runtimeClassName: gvisor
  containers:
  - name: app
    image: nginx:latest
```

```bash
# Commands
kubectl get runtimeclass
kubectl describe runtimeclass gvisor

# Check which runtime a Pod is using
kubectl get pod my-pod -o jsonpath='{.spec.runtimeClassName}'

# Node runtime info
kubectl get nodes -o custom-columns=NAME:.metadata.name,RUNTIME:.status.nodeInfo.containerRuntimeVersion
```

**Runtime Options:**
- containerd: default runtime.
- CRI-O: lightweight alternative.
- gVisor: sandboxed runtime.
- Kata Containers: VM-based isolation.

DevOps: What is Kubernetes RuntimeClass?