What is Kubernetes Pod Priority and Preemption?

Question

Accepted Answer

**Priority** — Pod importance ranking. **Preemption** — evict lower-priority Pods.

```yaml
# PriorityClass definitions
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: high-priority
value: 1000000
globalDefault: false
preemptionPolicy: PreemptLowerPriority
description: "Critical system pods"
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: medium-priority
value: 500000
globalDefault: false
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: low-priority
value: 100000
globalDefault: true
preemptionPolicy: Never  # Never preempt others
---
# Pod using priority
apiVersion: v1
kind: Pod
metadata:
  name: critical-task
spec:
  priorityClassName: high-priority
  containers:
  - name: app
    image: myapp:latest
    resources:
      requests:
        memory: "2Gi"
        cpu: "1000m"
```

```bash
# Commands
kubectl get priorityclass
kubectl describe priorityclass high-priority
kubectl get pods --sort-by=.spec.priority -A
kubectl get events --field-selector reason=Preempted
```

**Behavior:**
- Higher priority Pods can evict lower ones.
- PreemptionPolicy: Never prevents eviction.
- Evicted Pods get graceful shutdown.
- Priority classes are cluster-wide.

DevOps: What is Kubernetes Pod Priority and Preemption?