What is Kubernetes Pod QoS Classes?

Question

Accepted Answer

**QoS Classes** — quality of service tiers for Pods.

```yaml
# Guaranteed QoS
apiVersion: v1
kind: Pod
metadata:
  name: guaranteed-pod
spec:
  containers:
  - name: app
    image: nginx:latest
    resources:
      requests:
        cpu: "500m"
        memory: "256Mi"
      limits:
        cpu: "500m"   # Same as request
        memory: "256Mi" # Same as request
---
# Burstable QoS
apiVersion: v1
kind: Pod
metadata:
  name: burstable-pod
spec:
  containers:
  - name: app
    image: nginx:latest
    resources:
      requests:
        cpu: "250m"
        memory: "128Mi"
      limits:
        cpu: "500m"   # Higher than request
        memory: "256Mi" # Higher than request
---
# BestEffort QoS
apiVersion: v1
kind: Pod
metadata:
  name: besteffort-pod
spec:
  containers:
  - name: app
    image: nginx:latest
    # No requests or limits
```

```bash
# Check QoS class
kubectl get pod guaranteed-pod -o jsonpath='{.status.qosClass}'
kubectl get pod burstable-pod -o jsonpath='{.status.qosClass}'
kubectl get pod besteffort-pod -o jsonpath='{.status.qosClass}'

# View QoS classes
kubectl get pods -o custom-columns=NAME:.metadata.name,QOS:.status.qosClass

# Check eviction priority
kubectl get events --field-selector reason=Evicted --sort-by=.lastTimestamp

# Verify resource requests/limits
kubectl get pod guaranteed-pod -o jsonpath='{.spec.containers[0].resources}' | jq
```

**Classes:**
- Guaranteed: requests = limits (highest priority).
- Burstable: requests < limits.
- BestEffort: no requests/limits (lowest priority).

**Eviction Order:**
1. BestEffort (first to evict).
2. Burstable (if memory usage > requests).
3. Guaranteed (last to evict).

DevOps: What is Kubernetes Pod QoS Classes?