优先级与抢占

• 优先级是什么？
  • 优先级代表一个Pod相对其他Pod的重要性
• 优先级有什么用
  • 优先级可以保证重要的Pod被调用运行
• 如何使用优先级和抢占
  • 配置优先级类PriorityClass
  • 创建Pod是为其设置对应的优先级
• PriorityClass
  • PriorityClass是一个全局资源对象，它定义了从优先级类名称到优先级整数值的映射。优先级在values字段中指定，可以设置小于10亿的整数值，值越大，优先级越高
• PriorityClass还有两个可选字段：
  1. globaDefault：用于设置默认优先级状态，如果没有任何优先级设置，Pod的优先级为零
  2. description：用来配置描述性信息，告诉用户优先级的用途
• 优先级策略
  1. 非抢占优先：指的是在调度阶段优先进行调度分配，一旦容器调度完成就不可以抢占，资源不足时，只能等待，对应 preemptionPolicy: Never
  2. 抢占优先：强制调度一个Pod，如果资源不足无法被调度，调度程序会抢占(删除)较低优先级的Pod的资源，来保证高优先级Pod的运行，对应 preemptionPolicy: PreemptLowerPriority

非抢占优先级

# 定义优先级（队列优先）
[root@master ~]# vim mypriority.yaml
---
kind: PriorityClass					# 资源对象类型
apiVersion: scheduling.k8s.io/v1	# 资源对象版本
metadata:	
  name: high-non					# 优先级名称，可在Pod中引用
globalDefault: false				# 是否定义默认优先级（唯一）
preemptionPolicy: Never				# 抢占策略
value: 1000							# 优先级
description: non-preemptive			# 描述信息

---
kind: PriorityClass
apiVersion: scheduling.k8s.io/v1
metadata:
  name: low-non
globalDefault: false
preemptionPolicy: Never
value: 500
description: non-preemptive

[root@master ~]# kubectl apply -f mypriority.yaml 
priorityclass.scheduling.k8s.io/high-non created
priorityclass.scheduling.k8s.io/low-non created
[root@master ~]# kubectl get priorityclasses.scheduling.k8s.io 
NAME                      VALUE        GLOBAL-DEFAULT   AGE
high-non                  1000         false            12s
low-non                   500          false            12s
system-cluster-critical   2000000000   false            45h
system-node-critical      2000001000   false            45h

Pod资源文件

# 无优先级的 Pod
[root@master ~]# cat php1.yaml 
---
kind: Pod
apiVersion: v1
metadata:
  name: php1
spec:
  nodeSelector:
    kubernetes.io/hostname: node-0002
  containers:
  - name: php
    image: myos:phpfpm
    resources:
      requests:
        cpu: "1500m"

# 低优先级 Pod
[root@master ~]# cat php2.yaml 
---
kind: Pod
apiVersion: v1
metadata:
  name: php2
spec:
  nodeSelector:
    kubernetes.io/hostname: node-0002
  priorityClassName: low-non      # 指定优先级的名称
  containers:
  - name: php
    image: myos:phpfpm
    resources:
      requests:
        cpu: "1500m"

# 高优先级 Pod
[root@master ~]# cat php3.yaml 
---
kind: Pod
apiVersion: v1
metadata:
  name: php3
spec:
  nodeSelector:
    kubernetes.io/hostname: node-0002
  priorityClassName: high-non     # 指定优先级的名称
  containers:
  - name: php
    image: myos:phpfpm
    resources:
      requests:
        cpu: "1500m"

验证非抢占优先

[root@master ~]# kubectl apply -f php1.yaml 
pod/php1 created
[root@master ~]# kubectl apply -f php2.yaml 
pod/php2 created
[root@master ~]# kubectl apply -f php3.yaml 
pod/php3 created
[root@master ~]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
php1   1/1     Running   0          9s
php2   0/1     Pending   0          6s
php3   0/1     Pending   0          4s
[root@master ~]# kubectl delete pod php1
pod "php1" deleted
[root@master ~]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
php2   0/1     Pending   0          20s
php3   1/1     Running   0          18s

# 清理实验 Pod
[root@master ~]# kubectl delete pod php2 php3
pod "php2" deleted
pod "php3" deleted

抢占策略

[root@master ~]# vim mypriority.yaml
---
kind: PriorityClass
apiVersion: scheduling.k8s.io/v1
metadata:
  name: high
globalDefault: false
preemptionPolicy: PreemptLowerPriority
value: 1000
description: non-preemptive

---
kind: PriorityClass
apiVersion: scheduling.k8s.io/v1
metadata:
  name: low
globalDefault: false
preemptionPolicy: PreemptLowerPriority
value: 500
description: non-preemptive

[root@master ~]# kubectl apply -f mypriority.yaml 
priorityclass.scheduling.k8s.io/high created
priorityclass.scheduling.k8s.io/low created
[root@master ~]# kubectl get priorityclasses.scheduling.k8s.io 
NAME                      VALUE        GLOBAL-DEFAULT   AGE
high                      1000         false            12s
low                       500          false            12s
system-cluster-critical   2000000000   false            45h
system-node-critical      2000001000   false            45h

验证抢占优先级

# 默认优先级 Pod
[root@master ~]# kubectl apply -f php1.yaml 
pod/php1 created
[root@master ~]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
php1   1/1     Running   0          6s

# 高优先级 Pod
[root@master ~]# sed 's,-non,,' php3.yaml |kubectl apply -f - 
pod/php3 created
[root@master ~]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
php3   1/1     Running   0          9s

# 低优先级 Pod
[root@master ~]# sed 's,-non,,' php2.yaml |kubectl apply -f - 
pod/php2 created
[root@master ~]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
php2   0/1     Pending   0          3s
php3   1/1     Running   0          9s

# 清理实验 Pod
[root@master ~]# kubectl delete pod php2 php3
pod "php2" deleted
pod "php3" deleted
[root@master ~]# kubectl delete -f mypriority.yaml 
priorityclass.scheduling.k8s.io "high-non" deleted
priorityclass.scheduling.k8s.io "low-non" deleted
priorityclass.scheduling.k8s.io "high" deleted
priorityclass.scheduling.k8s.io "low" deleted