K8s-07: Scheduler

Published: November 26, 2023 by

Categories:
technology 47

Scheduler

调度过程

调度器从etcd中获取所有的node和pod信息。
调度器根据pod的spec和node的spec，过滤掉不符合要求的node。（predicate）
调度器根据node的spec和pod的spec，计算出每个node的优先级。(priority)
调度器将pod调度到优先级最高的node上。
调度器将pod的信息写入etcd中。
kubelet从etcd中获取pod的信息，然后创建pod。

predicate算法

PodFitsResources: 判断node上的资源是否满足pod的资源需求。
PodFitsHost: 判断pod是否被调度到指定的node上。
PodFitsHostPorts: 判断pod的端口是否被占用。
NoDiskConflict: 判断pod的volume是否和其他pod的volume冲突。
MatchNodeSelector: 判断node的label是否满足pod的nodeSelector。

priority算法

LeastRequestedPriority: 优先级最低的pod，优先被调度。
BalancedResourceAllocation: 资源分配最均衡的pod，优先被调度。
ImageLocalityPriority: 镜像在node上的缓存情况，优先被调度。

节点亲和性

硬策略：requiredDuringSchedulingIgnoredDuringExecution

  apiVersion: v1
  kind: Pod
  metadata:
      name: nginx
  spec:
      affinity:
      nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
              - key: disktype
              operator: In
              values:
              - ssd
      containers:
      - name: nginx
          image: nginx:1.14.2
          ports:
          - containerPort: 80

软策略：preferredDuringSchedulingIgnoredDuringExecution

  apiVersion: v1
  kind: Pod
  metadata:
      name: nginx
  spec:
      affinity:
      nodeAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 1
              preference:
              matchExpressions:
              - key: disktype
              operator: In
              values:
              - ssd
      containers:
      - name: nginx
          image: nginx:1.14.2
          ports:
          - containerPort: 80

pod亲和性

硬策略：requiredDuringSchedulingIgnoredDuringExecution

  apiVersion: v1
  kind: Pod
  metadata:
      name: nginx
  spec:
      affinity:
      podAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: security
              operator: In
              values:
              - S1
              topologyKey: failure-domain.beta.kubernetes.io/zone
      containers:
      - name: nginx
          image: nginx:1.14.2
          ports:
          - containerPort: 80

软策略：preferredDuringSchedulingIgnoredDuringExecution

  apiVersion: v1
  kind: Pod
  metadata:
      name: nginx
  spec:
      affinity:
      podAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 1
              podAffinityTerm:
              labelSelector:
                  matchExpressions:
                  - key: security     # pod的lable security in (S1)
                  operator: In
                  values:
                  - S1
              # node的lable failure-domain.beta.kubernetes.io/zone
              topologyKey: failure-domain.beta.kubernetes.io/zone     
      containers:
      - name: nginx
          image: nginx:1.14.2
          ports:
          - containerPort: 80

亲和性关系

调度策略	匹配标签	操作符	拓扑支持	调度目标
NodeAffinity	Node	In、NotIn、Exists、DoesNotExist, Gt, Lt	No	node
PodAffinity	Pod	In、NotIn、Exists、DoesNotExist	Yes	pod
PodAntiAffinity	Pod	In、NotIn、Exists、DoesNotExist	Yes	pod

Taint和Toleration
- Taint: 污点，node上的标签，用于标记node的特殊属性，如node上不运行pod。
- effect:
  - NoSchedule: 不允许调度pod到污点的node上。
  - PreferNoSchedule: 尽量不要调度pod到污点的node上。
  - NoExecute: 不允许调度pod到污点的node上，如果已经调度到污点的node上，会被驱逐。
- 举例：
```
  apiVersion: v1
  kind: Pod
  metadata:
      name: nginx
  spec:
      tolerations:
      - key: "key"
          operator: "Equal"
          value: "value"
          effect: "NoSchedule"
      containers:
      - name: nginx
          image: nginx:1.14.2
          ports:
          - containerPort: 80
```
- Toleration: 容忍度，pod上的标签，用于标记pod的特殊属性，如pod可以运行在污点的node上。key, value, effect必须和node上的taint匹配。且当operator为Exists时，value将被忽略。tolerationSeconds用于设置pod容忍污点的时间, 即被驱逐之前的时间。不指定key和effect时，表示容忍所有污点。

固定调度

使用spec.nodeName字段，将pod调度到指定的node上。

apiVersion: v1
kind: Pod
metadata:
    name: nginx
spec:
    nodeName: node01
    containers:
    - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

使用nodeSelector字段，将pod调度到匹配标签的node上。

apiVersion: v1
kind: Pod
metadata:
    name: nginx
spec:
    nodeSelector:
    disktype: ssd
    containers:
    - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80