[CKA] PriorityClass 란?

이번엔 PriorityClass 에 대해 정리하고자 한다.

 

1. 정의

- Pod 가 얼마나 중요한지(우선순위)를 정의하는 리소스

 

2. 특징

- 스케줄링 우선순위 결정

- Preemption(선점) 동작

  > 자원이 부족할 때 높은 우선순위 Pod 는 낮은 우선순위 Pod 를 제거(evict) 하여 자리를 차지할 수 있음

- 시스템 핵심 서비스 보호

  > kube-system 리소스처럼 중요한 Pod 는 높은 priority 로 설정해 노드 리소스 부족 시 제거되지 않도록 보호

 

3. 관련 문제 (KodeKloud 에서 제공하는 샘플 문제를 정리)

- Which of the following PriorityClasses are part of a default Kubernetes setup?

kubectl get priorityclass

 

- Create a PriorityClass named high-priority, a value of 100000, and a preemption policy of PreemptLowerPriority. Do not set this class as a global default.

vi high-priority.yaml

apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: high-priority
value: 100000
globalDefault: false
preemptionPolicy: PreemptLowerPriority

kubectl apply -f high-priority.yaml
kubectl get priorityclass

 

- In the default namespace, create a pod named low-prio-pod that runs an nginx image and uses the low-priority PriorityClass.

vi low-prio-pod.yaml

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

kubectl apply -f low-prio-pod.yaml

 

- To resolve this situation and get the critical-app to a running state, you should:

  > Assign the high-priority class to the critical-app. Delete and recreate the pod with the new priority. Make sure the pod is in running state after applying the actions.

kubectl get pod critical-app -o yaml > critical-app.yaml
-- add priorityClassName: high-priority under the spec field.
-- remove the line priority: 0 if it exists in the spec to avoid conflicting priority settings.
kubectl delete pod critical-app
kubectl apply -f critical-app.yaml
kubectl get pod critical-app

 

4. 출처

- https://learn.kodekloud.com/user/courses/udemy-labs-certified-kubernetes-administrator-with-practice-tests