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Kubernetes 之 Pod 标签、节点选择器和节点亲和性

作者：AllinToyou | 2024-05-23 12:08:34

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Kubernetes 之 Pod 标签、节点选择器和节点亲和性

Kubernetes 之 Pod 标签、节点选择器和节点亲和性

标签的定义

标签其实就一对 key-value 键值对，被关联到资源对象上。在 Pod 中，标签可以标记该 Pod 的特形，例如该 Pod 的功能、版本等等以便于我们对 Pod 进行分组管理。标签可以在新建 Pod 的时候直接定义，也可以动态修改。每个 Pod 可以拥有多个标签，但是key值必须是唯一的。

标签的使用

# 查看 test 空间下所有 Pod 的标签
root@k8s-master1:~# kubectl get pods -n test --show-labels
NAME       READY   STATUS    RESTARTS   AGE   LABELS
k8s-test   1/1     Running   0          16s   app=k8s-test,feature=nginx

# 给 k8s-test 新增标签
root@k8s-master1:~# kubectl label -ntest pods/k8s-test version=1.0
pod/k8s-test labeled

# 查看 k8s-test Pod 的所有标签
root@k8s-master1:~# kubectl get pods/k8s-test -ntest --show-labels
NAME       READY   STATUS    RESTARTS   AGE   LABELS
k8s-test   1/1     Running   0          10m   app=k8s-test,feature=nginx,version=1.0

# 查看标签 version=1.0 的所有 Pod
root@k8s-master1:~# kubectl get pods -n test -l version=1.0
NAME       READY   STATUS    RESTARTS   AGE
k8s-test   1/1     Running   0          12m

# 查看具有 version 键的标签
root@k8s-master1:~# kubectl get pods -ntest -l version
NAME       READY   STATUS    RESTARTS   AGE
k8s-test   1/1     Running   0          13m
root@k8s-master1:~# kubectl get pods -ntest -L version
NAME       READY   STATUS    RESTARTS   AGE   VERSION
k8s-test   1/1     Running   0          14m   1.0

# 修改 version 键为 2.0
root@k8s-master1:~# kubectl label --overwrite -n test pods k8s-test version=2.0
pod/k8s-test labeled
root@k8s-master1:~# kubectl get pods k8s-test -L version -n test
NAME       READY   STATUS    RESTARTS   AGE   VERSION
k8s-test   1/1     Running   0          18m   2.0

# 移除 version 标签
root@k8s-master1:~# kubectl label pods -n test k8s-test version-
pod/k8s-test unlabeled
root@k8s-master1:~# kubectl get pods k8s-test --show-labels -n test
NAME       READY   STATUS    RESTARTS   AGE   LABELS
k8s-test   1/1     Running   0          22m   app=k8s-test,feature=nginx

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节点选择器的定义

我们在创建 Pod 资源的时候，Pod 会根据 Scheduler 进行调度，默认会调度到随机的一个工作节点。如果我们想要将 Pod 调度到指定节点或者调度到一些具有相同特点的 Node 节点，可以使用 Pod 中的 nodeName 或者 nodeSelector 字段来指定要调度到的 Node 节点。

节点选择器的使用

  1. 配置nodeName在 k8s-master1 节点上。原则上控制节点不分配业务 Pod ，但是nodeName优先级很高，可能将其指定到 控制节点上。

    apiVersion: v1
kind: Pod
metadata:
  name: k8s-test
  namespace: test
  labels:
    app: k8s-test
    feature: nginx
spec:
  nodeName: k8s-master1
  containers:
    - name:  k8s-test
      ports:
        - containerPort: 80
      image: k8s-test:v1.0
      imagePullPolicy: IfNotPresent
      resources:
        requests:
          memory: "1Gi"
          cpu: "1"
        limits:
          memory: "2Gi"
          cpu: "2"

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    # 查看 Pod
root@k8s-master1:~# kubectl get pods -owide -ntest
NAME       READY   STATUS    RESTARTS   AGE   IP               NODE          NOMINATED NODE   READINESS GATES
k8s-test   1/1     Running   0          90s   10.244.159.137   k8s-master1   <none>           <none>

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  2. 给 k8s-worker2 节点创建 os=debian和env=test两个标签

    root@k8s-master1:~# kubectl label nodes k8s-worker2 os=debian env=test -ntest
node/k8s-worker2 labeled
root@k8s-master1:~# kubectl get nodes k8s-worker2 --show-labels
NAME          STATUS   ROLES    AGE    VERSION   LABELS
k8s-worker2   Ready    <none>   3d4h   v1.29.4   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,env=test,kubernetes.io/arch=amd64,kubernetes.io/hostname=k8s-worker2,kubernetes.io/os=linux,os=debian

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  3. 测试nodeName和nodeSelector并存的情况

    apiVersion: v1
kind: Pod
metadata:
  name: k8s-test
  namespace: test
  labels:
    app: k8s-test
    feature: nginx
spec:
  nodeName: k8s-master1
  nodeSelector:
    os: debian
    env: test
  containers:
    - name:  k8s-test
      ports:
        - containerPort: 80
      image: k8s-test:v1.0
      imagePullPolicy: IfNotPresent
      resources:
        requests:
          memory: "1Gi"
          cpu: "1"
        limits:
          memory: "2Gi"
          cpu: "2"

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    root@k8s-master1:~# kubectl describe pods k8s-test -ntest
Name:             k8s-test
Namespace:        test
Priority:         0
Service Account:  default
Node:             k8s-master1/192.168.31.60
Start Time:       Thu, 16 May 2024 13:04:07 +0800
Labels:           app=k8s-test
                  feature=nginx
Annotations:      cni.projectcalico.org/podIP:
                  cni.projectcalico.org/podIPs:
Status:           Failed
Reason:           NodeAffinity
Message:          Pod was rejected: Predicate NodeAffinity failed

# 这里说明条件冲突，导致创建失败。将 nodeName 修改为 k8s-worker2 后成功
root@k8s-master1:~# kubectl get pods -ntest
NAME       READY   STATUS    RESTARTS   AGE
k8s-test   1/1     Running   0          6s

# 将 nodeName 去除，将 nodeSelect 中 os=windows
root@k8s-master1:~# kubectl describe pods k8s-test -ntest
Events:
  Type     Reason            Age   From               Message
  ----     ------            ----  ----               -------
  Warning  FailedScheduling  22s   default-scheduler  0/3 nodes are available: 1 node(s) had untolerated taint {node-role.kubernetes.io/control-plane: }, 2 node(s) didn't match Pod's node affinity/selector. preemption: 0/3 nodes are available: 3 Preemption is not helpful for scheduling.
  
# 综上可见,所有条件均是与的关系

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    节点亲和性的定义

    节点亲和性是 Pod 在调度过程中一系列调度约束规则，主要针对节点选择器的匹配，匹配度越高，则该节点执行该 Pod 的概率就越高。节点亲和性分为硬亲和性requiredDuringSchedulingIgnoredDuringExecution和软亲和性preferredDuringSchedulin $Data2012

    gIgnoredDuringExecution，硬亲和性代表必须满足，软亲和性在不满足约束规则的条件上，仍可以随机启动。

    硬亲和性使用

    apiVersion: v1
kind: Pod
metadata:
  name: node-hard-affinity
  namespace: default
  labels:
    app: k8s-test
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
          - key: role
            operator: In
            values:
            - worker
  containers:
  - name: k8s-test
    image: k8s-test:v1.0
    imagePullPolicy: IfNotPresent
    ports:
    - containerPort: 80

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    root@k8s-master1:~# kubectl get node -L role
NAME          STATUS   ROLES           AGE    VERSION   ROLE
k8s-master1   Ready    control-plane   4d7h   v1.29.4
k8s-worker1   Ready    <none>          4d7h   v1.29.4
k8s-worker2   Ready    <none>          4d7h   v1.29.4   worker
root@k8s-master1:~# kubectl get pods -owide
NAME                 READY   STATUS    RESTARTS   AGE    IP              NODE          NOMINATED NODE   READINESS GATES
node-hard-affinity   1/1     Running   0          2m5s   10.244.126.12   k8s-worker2   <none>           <none>

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    软亲和性使用

    metadata:
  name: node-soft-affinity
  namespace: default
  labels:
    app: k8s-test
spec:
  affinity:
    nodeAffinity:
      preferredDuringSchedulingIgnoredDuringExecution:
      - preference:
          matchExpressions:
          - key: memory
            operator: Lt
            values:
            - "2048"
        weight: 20 # 权重，区间在1-100，谁权重高就选谁
      - preference:
          matchExpressions:
          - key: memory
            operator: Gt
            values:
            - "2048"
        weight: 10
  containers:
  - name: k8s-test
    image: k8s-test:v1.0
    imagePullPolicy: IfNotPresent
    ports:
    - containerPort: 80

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    # 本 Pod 亲和内存大于 2048 和内存小于 2048 的两种情况，但小于 2048 的节点权重更大
root@k8s-master1:~# kubectl get nodes -L memory
NAME          STATUS   ROLES           AGE     VERSION   MEMORY
k8s-master1   Ready    control-plane   4d13h   v1.29.4
k8s-worker1   Ready    <none>          4d12h   v1.29.4   1024
k8s-worker2   Ready    <none>          4d12h   v1.29.4   4096
root@k8s-master1:~# kubectl get pods -owide
NAME                 READY   STATUS    RESTARTS   AGE    IP              NODE          NOMINATED NODE   READINESS GATES
node-soft-affinity   1/1     Running   0          2m7s   10.244.194.80   k8s-worker1   <none>           <none>

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