参考：
K8S - Assign Pods to Nodes using Node Affinity
K8S - Assigning Pods to Nodes

一、node亲和性

node亲和性策略表示pod部署到符合某些条件的node上.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: name
                operator: In
                values:
                - nginx1
                - nginx2
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 1
            preference:
              matchExpressions:
              - key: app
                operator: In
                values:
                - nginx
      containers:
      - name: nginx-server
        image: nginx:latest

上面的这个例子表示pod必须部署到满足nodeSelectorTerms中的条件,尽量满足preference中的条件.

• nodeAffinity表示pod和node的亲和性策略
• nodeSelectorTerms 表示打了这些标签的node上才能部署pod,这里的key values都可以指定多个值,可以实现类似nodeSelector的或的操作.
• preference 表示最好部署到满足这些条件的node上.
• 注意
  requiredDuringSchedulingIgnoredDuringExecution -> nodeSelectorTerms
preferredDuringSchedulingIgnoredDuringExecution -> preference
  两套组合

策略

1. requiredDuringSchedulingIgnoredDuringExecution
   硬策略表示调度过程必须满足执行过程忽略

2. preferredDuringSchedulingIgnoredDuringExecution
   软策略表示调度过程尽量满足执行过程忽略

操作符

这里的匹配逻辑是label在某个列表中，可选的操作符有：

• In: label的值在某个列表中
• NotIn：label的值不在某个列表中
• Exists：某个label存在
• DoesNotExist：某个label不存在
• Gt：label的值大于某个值（字符串比较）
• Lt：label的值小于某个值（字符串比较）

二、pod亲和性、反亲和性

pod亲和性和非亲和性表示pod部署到或不部署到满足某些label的pod所在的node上.

apiVersion: v1
kind: Pod
metadata:
  name: with-pod-affinity
spec:
  affinity:
    podAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchExpressions:
          - key: security
            operator: In
            values:
            - S1
        topologyKey: topology.kubernetes.io/zone
    podAntiAffinity:
      preferredDuringSchedulingIgnoredDuringExecution:
      - weight: 100
        podAffinityTerm:
          labelSelector:
            matchExpressions:
            - key: security
              operator: In
              values:
              - S2
          topologyKey: topology.kubernetes.io/zone
  containers:
  - name: with-pod-affinity
    image: k8s.gcr.io/pause:2.0

• podAffinity表示pod亲和性，即将当前pod部署到node上，且此node上的其他pod需要满足labelSelector指定的条件
• podAntiAffinity表示pod反亲和性，即将当前pod部署到node上，且此node上的其他pod不满足labelSelector指定的条件
• toplogyKey用来指定节点的label，即包含该label的节点才满足调度条件（用于划分zone），默认可以使用：kubernetes.io/hostname
• pod亲和性仅支持：In, NotIn, Exists, DoesNotExist
• 策略同node亲和性：requiredDuringSchedulingIgnoredDuringExecution, preferredDuringSchedulingIgnoredDuringExecution

实际使用中，亦可以实现：

1. 同一个deployment下的多个pod分别部署到不同的node上，实现服务的高可用性（podAntiAffinity）
2. 将相关联的服务部署到同一个node上，如web和存储（podAffinity）
3. 亦可将1和2结合，即使用podAntiAffinity来分散同一deployment的不同pod实例到不同node以实现服务高可用，同时使用podAffinity来使得相关联的服务都部署在同一个节点，减少网络通信。

具体示例参见：https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#more-practical-use-cases

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-
spec:
  selector:
    matchLabels:
      app: store
  replicas: 3
  template:
    metadata:
      labels:
        app: store
    spec:
      affinity:
        # 使用pod反亲和性podAntiAffinity
        # 即同一deployment下的replicas个pod分散到不同的node上
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              # 即相同标签app: store互相排斥
              matchExpressions:
              - key: app
                operator: In
                values:
                - store
            topologyKey: "kubernetes.io/hostname"
      containers:
      - name: redis-server
        image: redis:3.2-alpine
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-server
spec:
  selector:
    matchLabels:
      app: web-store
  replicas: 3
  template:
    metadata:
      labels:
        app: web-store
    spec:
      affinity:
        # 使用pod反亲和性podAntiAffinity
        # 即同一deployment下的relicas个pod分散到不同的node上
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              # 即相同标签app: web-store互相排斥
              matchExpressions:
              - key: app
                operator: In
                values:
                - web-store
            topologyKey: "kubernetes.io/hostname"
        # 使用pod亲和性podAffinity
        # 即当前deployment下的replicas个pod需要部署到node上
        # 且node上需要运行包含标签app: store的pod
        # 即web-store自身分散到不同的node上（podAntiAffinity），且分散到的node上还需要运行redis-cache（podAffinity）
        podAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - store
            topologyKey: "kubernetes.io/hostname"
      containers:
      - name: web-app
        image: nginx:1.16-alpine