调度之pod反亲和性（podAntiAffinity）

1.简介

Pod 反亲和性（podAntiAffinity）则是反着来的，比如一个节点上运行了某个 Pod，那么我们的模板 Pod 则不希望被调度到这个节点上面去了。我们把上面的 podAffinity 直接改成 podAntiAffinity：(pod-antiaffinity-demo.yaml)

apiVersion: apps/v1
kind: Deployment
metadata:
  name: pod-antiaffinity
  labels:
    app: pod-antiaffinity
spec:
  replicas: 3
  selector:
    matchLabels:
      app: pod-antiaffinity
  template:
    metadata:
      labels:
        app: pod-antiaffinity
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
          name: nginxweb
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:  # 硬策略
          - labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - busybox-pod
            topologyKey: kubernetes.io/hostname

这里的意思就是如果一个节点上面有一个 app=busybox-pod 这样的 Pod 的话，那么我们的 Pod 就别调度到这个节点上面来，上面我们把app=busybox-pod 这个 Pod 固定到了 node2 这个节点上面的，所以正常来说我们这里的 Pod 不会出现在该节点上：

[root@k8s-master01 ~]# kubectl get pod -owide
NAME                                READY   STATUS              RESTARTS   AGE     IP               NODE           NOMINATED NODE   READINESS GATES
busybox                             1/1     Running             264        11d     172.17.125.9     k8s-node01     <none>           <none>
nginx-68db656dd8-mprnc              1/1     Running             0          74m     172.17.125.13    k8s-node01     <none>           <none>
nginx-68db656dd8-znwgp              1/1     Running             1          11d     172.18.195.11    k8s-master03   <none>           <none>
pod-antiaffinity-7bb9c7ff57-4l8dt   1/1     Running             0          17s     172.17.125.16    k8s-node01     <none>           <none>
pod-antiaffinity-7bb9c7ff57-kq4gj   0/1     ContainerCreating   0          17s     <none>           k8s-node01     <none>           <none>
pod-antiaffinity-7bb9c7ff57-zhg2q   1/1     Running             0          17s     172.25.244.217   k8s-master01   <none>           <none>
test-busybox                        1/1     Running             0          23m     172.27.14.239    k8s-node02     <none>           <none>
web                                 2/2     Running             0          3d19h   172.18.195.14    k8s-master03   <none>           <none>

我们可以看到没有被调度到 node2 节点上，因为我们这里使用的是 Pod 反亲和性。大家可以思考下，如果这里我们将拓扑域更改成 beta.kubernetes.io/os 会怎么样呢？答案是:Pending

[root@k8s-master01 ~]# kubectl get pod -owide
NAME                                READY   STATUS    RESTARTS   AGE     IP              NODE           NOMINATED NODE   READINESS GATES
busybox                             1/1     Running   264        11d     172.17.125.9    k8s-node01     <none>           <none>
nginx-68db656dd8-mprnc              1/1     Running   0          77m     172.17.125.13   k8s-node01     <none>           <none>
nginx-68db656dd8-znwgp              1/1     Running   1          11d     172.18.195.11   k8s-master03   <none>           <none>
pod-antiaffinity-64bf798fb6-dvhh2   0/1     Pending   0          9s      <none>          <none>         <none>           <none>
pod-antiaffinity-64bf798fb6-rg2pc   0/1     Pending   0          9s      <none>          <none>         <none>           <none>
pod-antiaffinity-64bf798fb6-ttnbp   0/1     Pending   0          9s      <none>          <none>         <none>           <none>
test-busybox                        1/1     Running   0          25m     172.27.14.239   k8s-node02     <none>           <none>
web                                 2/2     Running   0          3d19h   172.18.195.14   k8s-master03   <none>           <none>