What are Kubernetes QoS Classes?

Question

Accepted Answer

**QoS (Quality of Service) Classes** — Pod priority during resource shortage.

**Three classes:**

**1. Guaranteed (highest):**
```yaml
spec:
  containers:
    - name: app
      resources:
        requests:
          cpu: "500m"
          memory: "256Mi"
        limits:
          cpu: "500m"      # limits == requests
          memory: "256Mi"  # limits == requests
```

**2. Burstable (medium):**
```yaml
spec:
  containers:
    - name: app
      resources:
        requests:
          cpu: "250m"
          memory: "128Mi"
        limits:
          cpu: "500m"      # limits > requests
          memory: "256Mi"
```

**3. BestEffort (lowest):**
```yaml
spec:
  containers:
    - name: app
      # No requests and limits
```

**OOM-kill order:**
1. BestEffort (killed first).
2. Burstable.
3. Guaranteed (killed last).

**Verification:**
```bash
kubectl get pods -o custom-columns=NAME:.metadata.name,QOS:.status.qosClass
kubectl describe pod my-pod | grep -i qos
```

**Recommendations:**
- Production services → Guaranteed.
- Batch jobs → BestEffort.
- Development → Burstable.

DevOps: What are Kubernetes QoS Classes?