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Kubernetes: Pod - PriorityClass

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• Kubernetes: Pod - PriorityClass
  • PriorityClass
    • Imperative Command
    • Declarative Manifest
  • Lab: Priority Class
    • Default Priority Class
    • Create Priority Class

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PriorityClass

• PriorityClass

  • a cluster-scoped object that assigns an integer priority to pods.
  • No-namespaced objects
    • no created within a specific namespace

• Priority:

  • Higher numbers = higher priority.
  • Control plane components range
    • system-node-critical: 2,000,001,000
    • system-cluster-critical: 2,000,000,000
  • User-Defined Range:
    • -2,147,483,648 - 1,000,000,000

• Priority Value

  • By default: 0
  • Custom default priority
    • by creating a PriorityClass with globalDefault: true
    • can only be define in one PriorityClass

• Behaviaor:

  • When the cluster is short on resources, the scheduler may preempt (evict) lower-priority pods to make room for higher-priority ones.

• Preemption Policy:

  • PreemptLowerPriority:
    • default
      • preempt (evict) the existing lower-priority pods
  • never:
    • no action,
    • wait for the resources to free up

• Purpose:

  • Ensure critical workloads (e.g., ingress, DNS, controllers) get scheduled first.
  • Let batch/BestEffort jobs yield to user-facing services during pressure.
  • Provide a sensible default priority for “everything else.”

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Imperative Command

CMD	DESC
kubectl get priorityclass/kubectl get pc	List priorityclass
kubectl delete pc NAME	Delete priorityclass

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Declarative Manifest

• Create a pc

apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: high-priority
value: 1000000000
description: "Critical platform services."
preemptionPolicy: PreemptLowerPriority
globalDefault: false

• Associate with pod

# pod
spec:
  priorityClassName: high-priority

---

Lab: Priority Class

Default Priority Class

kubectl get pc
# NAME                      VALUE        GLOBAL-DEFAULT   AGE   PREEMPTIONPOLICY
# system-cluster-critical   2000000000   false            36d   PreemptLowerPriority
# system-node-critical      2000001000   false            36d   PreemptLowerPriority

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Create Priority Class

# demo-priorityclass.yaml
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: high-priority
value: 100000
preemptionPolicy: PreemptLowerPriority

---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: low-priority
value: 1000
preemptionPolicy: PreemptLowerPriority

• Create pod

# demo-priorityclass-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: low-priority-pod
spec:
  priorityClassName: low-priority # specify priority
  containers:
    - image: nginx
      name: nginx

---
apiVersion: v1
kind: Pod
metadata:
  name: high-prio-pod
spec:
  priorityClassName: high-priority # specify priority
  containers:
    - image: nginx
      name: nginx

kubectl apply -f demo-priorityclass.yaml
# priorityclass.scheduling.k8s.io/high-priority created
# priorityclass.scheduling.k8s.io/low-priority created

kubectl apply -f demo-priorityclass-pod.yaml
# pod/low-priority-pod created
# pod/high-prio-pod created


kubectl get pods -o custom-columns="NAME:.metadata.name,PRIORITY:.spec.priorityClassName"
# NAME            PRIORITY
# high-prio-pod   high-priority
# low-prio-pod    low-priority