[DAY14]Label進階使用-Affinity and anti-affinity

2021 iThome 鐵人賽

DAY 14

DevOps

k8s新手船長船難記系列第 14 篇

13th鐵人賽

熱血奶爸v0.0.1

團隊神龍特攻隊 - it 宏的逆襲

2021-09-22 08:47:26

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把pod部署到特定node上面

k8s的特性來說，基本上部署到k8s一定是會挑資源最輕的那台node優先，所以pod會分散至各個node上面，
如果今天使用環境上面需要把pod分配到特定的node上面時，要怎麼做呢？

請繼續看下去~~

先來看node上面有沒有label

kubectl get nodes --show-labels
NAME                           STATUS   ROLES                  AGE     VERSION   LABELS
k8s-playground-control-plane   Ready    control-plane,master   4m45s   v1.21.1   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=k8s-playground-control-plane,kubernetes.io/os=linux,node-role.kubernetes.io/control-plane=,node-role.kubernetes.io/master=,node.kubernetes.io/exclude-from-external-load-balancers=
k8s-playground-worker          Ready    <none>                 4m16s   v1.21.1   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=k8s-playground-worker,kubernetes.io/os=linux
k8s-playground-worker2         Ready    <none>                 4m17s   v1.21.1   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=k8s-playground-worker2,kubernetes.io/os=linux

給work上個high-vm的label,work2給個backend-only的label

kubectl label nodes k8s-playground-worker use=high-vm  
node/k8s-playground-worker labeled

kubectl label nodes k8s-playground-worker2 use=backend-only
node/k8s-playground-worker2 labeled

查看一下是否都被加上label了

kubectl get nodes --show-labels   
k8s-playground-worker          Ready    <none>                 6m10s   v1.21.1   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=k8s-playground-worker,kubernetes.io/os=linux,use=high-vm
k8s-playground-worker2         Ready    <none>                 6m11s   v1.21.1   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=k8s-playground-worker2,kubernetes.io/os=linux,use=backend-only

這樣子我二台node都有不同的label了，一樣用前面的redis來部署。
從下圖可以看的出來二個pod被分別部署至不同node上面

現在我再來部署二個redis到high-vm這個label的node上面

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-redis-backend1
  labels:
    app.kubernetes.io/name: my-redis
    env: dev
    user: backend
spec:
  serviceName: my-redis-backend1
  replicas: 1
  selector:
    matchLabels:
       app.kubernetes.io/name: my-redis
  template:
    metadata:
      labels:
        app.kubernetes.io/name: my-redis
        env: dev
        user: backend
    spec:
      containers:
        - name: my-redis-backend1
          image: "redis:latest"
          imagePullPolicy: IfNotPresent
          args: ["--appendonly", "yes", "--save", "600", "1"]
          ports:
            - name: redis
              containerPort: 6379
              protocol: TCP
          volumeMounts:
            - name: data
              mountPath: /data
          resources: {}
      nodeSelector: #加這個
        use: high-vm

  volumeClaimTemplates:
      - metadata:
          name: data
        spec:
          accessModes: ["ReadWriteOnce"]
          resources:
            requests:
              storage: 1Gi
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-redis-frontend1
  labels:
    app.kubernetes.io/name: my-redis
    env: dev
    user: frontend
spec:
  serviceName: my-redis-frontend1
  replicas: 1
  selector:
    matchLabels:
       app.kubernetes.io/name: my-redis
  template:
    metadata:
      labels:
        app.kubernetes.io/name: my-redis
        env: dev
        user: frontend
    spec:
      containers:
        - name: my-redis-frontend1
          image: "redis:latest"
          imagePullPolicy: IfNotPresent
          args: ["--appendonly", "yes", "--save", "600", "1"]
          ports:
            - name: redis
              containerPort: 6379
              protocol: TCP
          volumeMounts:
            - name: data
              mountPath: /data
          resources: {}
      nodeSelector: #加這個
        use: high-vm

  volumeClaimTemplates:
      - metadata:
          name: data
        spec:
          accessModes: ["ReadWriteOnce"]
          resources:
            requests:
              storage: 1Gi

來確認是否都部署至use=high-vm這台node呢。
從下圖可以看到新增二個redis都部署到worker這台node上面

Node Affinity and anti-affinity

親和力(Affinity) 和反親和力(anti-affinity)，因為正好是相反的行為，所以就單純以Affinity來說明，
親和力跟上面寫的Node Selector有點像，但是Node Selector無法進行條件設定。
Affinity有二種條件設定模式

requiredDuringSchedulingIgnoredDuringExecution :字首看到required，表示這種設定模式是一定要有符合的條件才能把pod部署上去，如果都沒有符合條件的node時就會發生錯誤
preferredDuringSchedulingIgnoredDuringExecution :這種就是如果有符合條件就照條件部署到對應node，如果沒有符合的node一樣還是能部署。

一樣用上面的yaml說明

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-redis-backend1
  labels:
    app.kubernetes.io/name: my-redis
    env: dev
    user: backend
spec:
  serviceName: my-redis-backend1
  replicas: 1
  selector:
    matchLabels:
       app.kubernetes.io/name: my-redis
  template:
    metadata:
      labels:
        app.kubernetes.io/name: my-redis
        env: dev
        user: backend
    spec:
      containers:
        - name: my-redis-backend1
          image: "redis:latest"
          imagePullPolicy: IfNotPresent
          args: ["--appendonly", "yes", "--save", "600", "1"]
          ports:
            - name: redis
              containerPort: 6379
              protocol: TCP
          volumeMounts:
            - name: data
              mountPath: /data
          resources: {}
      affinity: #親和力設定
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution: # node必需符合這條件
            nodeSelectorTerms:
            - matchExpressions: #條件為use=backend-only
              - key: use
                operator: In
                values:
                - "backend-only"

  volumeClaimTemplates:
      - metadata:
          name: data
        spec:
          accessModes: ["ReadWriteOnce"]
          resources:
            requests:
              storage: 1Gi
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-redis-frontend1
  labels:
    app.kubernetes.io/name: my-redis
    env: dev
    user: frontend
spec:
  serviceName: my-redis-frontend1
  replicas: 1
  selector:
    matchLabels:
       app.kubernetes.io/name: my-redis
  template:
    metadata:
      labels:
        app.kubernetes.io/name: my-redis
        env: dev
        user: frontend
    spec:
      containers:
        - name: my-redis-frontend1
          image: "redis:latest"
          imagePullPolicy: IfNotPresent
          args: ["--appendonly", "yes", "--save", "600", "1"]
          ports:
            - name: redis
              containerPort: 6379
              protocol: TCP
          volumeMounts:
            - name: data
              mountPath: /data
          resources: {}
      affinity:
        nodeAffinity:
          preferredDuringSchedulingIgnoredDuringExecution: #如果有符合條件時就部署到對應node
          - weight: 70 #權重70分
            preference: 
              matchExpressions: 
              - key: use
                operator: In
                values:
                - "high-vm"
          - weight: 30 #權重30分
            preference: 
              matchExpressions: 
              - key: use
                operator: In
                values:
                - "backend-only"

  volumeClaimTemplates:
      - metadata:
          name: data
        spec:
          accessModes: ["ReadWriteOnce"]
          resources:
            requests:
              storage: 1Gi

Pod Affinity and anti-affinity

簡單說pod與pod的連結(?)，如果部署的情形需要某個pod跟某個pod必需是cp，不能拆散時，就可以使用pod Affinity來實作
把原本的nodeAffinity改成podAffinity

affinity:
        podAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - topologyKey: kubernetes.io/hostname
            labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - test-pod-Affinity

這樣子這個pod就會去找尋它的真命天子(?)
如果需要更多資訊可以到下面的網站查詢喔
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