1、概念

在定義pod時，可以在spec.priorityClassName中指定PriorityClass，根據其中定義的優先順序在PrioritySort中排序，優先排程優先順序高的pod，優先順序相同的pod根據進入佇列的時間戳先後排程，當未找到

合適的執行節點時，排程器會將POD轉為pending狀態，併為其啟動“搶佔”過程，在叢集中刪除一個或者多個低優先的POD，讓節點滿足該優先順序高的POD排程。

pod優先順序使用32位正整數，可用值為[0,1000000000],值越大優先順序越高，大於1000000000的優先順序預留給系統級的關鍵pod，以防止這些pod被驅逐。

例如：API-server，Controller-manager，Scheduler和etcd 的pod直接使用system-cluster-critical PriorityClass，優先順序為：2000000000

metric-server,CoreDNS、Dashboard等使用system-node-critical 的pod使用system-node-critical PriorityClass,優先順序為：2000001000

在定義pod時不定義PriorityClass時，預設優先順序的值為：0

2、PriorityClass定義

如果叢集上存在多個設定了全域性預設的優先順序的PriorityClass物件，優先順序小的會生效，如：

定義預設優先順序的demoappv11

apiVersion: apps/v1
kind: Deployment
metadata:
  name: demoappv11
spec:
  replicas: 4
  selector:
    matchLabels:
      app: demoappv11
  template:
    metadata:
      labels:
        app: demoappv11
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - {key: app, operator: In, values: ["demoappv11"]}
            topologyKey: kubernetes.io/hostname
      containers:
      - name: demoappv11
        image: harbor.myland.com/baseimages/centos/centos-tsinghua:7.9.2009 
        command: ["sleep","1000"]
        resources:
          requests:
            memory: 2Gi
            cpu: 150m
 

優先順序為222222的demoappv12

kind: PriorityClass
apiVersion: scheduling.k8s.io/v1
metadata:
  name: demoappv12
value: 222222
description: "demoappv12"
globalDefault: false
preemptionPolicy: PreemptLowerPriority
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: demoappv12
spec:
  replicas: 4
  selector:
    matchLabels:
      app: demoappv12
  template:
    metadata:
      labels:
        app: demoappv12
    spec:
      priorityClassName: demoappv12
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - {key: app, operator: In, values: ["demoappv12"]}
            topologyKey: kubernetes.io/hostname
      containers:
      - name: demoappv12
        image: ikubernetes/demoapp:v1.2
        resources:
          requests:
            memory: 2Gi
            cpu: 150m
 

由於記憶體不足，排程器開始清理優先順序的demoappv11

直到demoappv11處於pending狀態