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DaemonSet

Kubernetes
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2023-12-05
DaemonSet

DaemonSet 用于在每个节点部署一个 Pod，随着集群节点新增而自动新增 Pod，随着集群节点删除而删除 Pod，通常情况下 Master 节点没有，因为 Master 节点通常存在污点，在没有特殊设置的情况下不会运行

那么在哪种情况下我们会需要用到这种业务场景呢？其实这种场景还是比较普通的，比如：

  • 集群存储守护程序，如 glusterd、ceph 要部署在每个节点上以提供持久性存储；
  • 节点监控守护进程，如 Prometheus 监控集群，可以在每个节点上运行一个 node-exporter 进程来收集监控节点的信息；
  • 日志收集守护程序，如 fluentd 或 logstash，在每个节点上运行以收集容器的日志
  • 节点网络插件，比如 flannel、calico，在每个节点上运行为 Pod 提供网络服务。

使用 DaemonSet 创建的服务，可以在调度服务没有起来是使用，因为 DaemonSet 控制器会默认给 Pod 指定 .spec.nodeName

DaemonSet 资源实例：

# nginx-ds.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: nginx-ds
  namespace: default
spec:
  selector:
    matchLabels:
      k8s-app: nginx
  template:
    metadata:
      labels:
        k8s-app: nginx
    spec:
      containers:
      - image: nginx:1.7.9
        name: nginx
        ports:
        - name: http
          containerPort: 80

使用实例创建资源，并且查看 Pod 列表

[root@kube01 ds]# kubectl apply -f nginx-ds.yaml
daemonset.apps/nginx-ds created

[root@kube01 ds]# kubectl get pod -l k8s-app=nginx
NAME             READY   STATUS    RESTARTS   AGE
nginx-ds-4vnht   1/1     Running   0          57s

这是我们发现 Pod 只有一个，但是我们的集群却有两个节点，这是因为 Master 节点存在污点，需要给 DaemonSet 设置容忍污点

# nginx-ds.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: nginx-ds
  namespace: default
spec:
  selector:
    matchLabels:
      k8s-app: nginx
  template:
    metadata:
      labels:
        k8s-app: nginx
    spec:
      containers:
      - image: nginx:1.7.9
        name: nginx
        ports:
        - name: http
          containerPort: 80
      tolerations:
      - key: "node-role.kubernetes.io/master"
        operator: "Exists"
        effect: "NoSchedule"

此时发现 Master 节点也已经存在 Pod

通过 describe 查看 Pod 发现 Controlled By 属于 DaemonSet，由此发现 DaemonSet 也是直接控制 Pod

[root@kube01 ds]# kubectl describe pod nginx-ds-2nx9s
Name:         nginx-ds-2nx9s
Namespace:    default
Priority:     0
Node:         kube01/192.168.17.42
Start Time:   Tue, 13 Jun 2023 14:48:44 +0800
Labels:       controller-revision-hash=867c95757d
              k8s-app=nginx
              pod-template-generation=2
Annotations:  <none>
Status:       Running
IP:           172.30.0.6
IPs:
  IP:           172.30.0.6
Controlled By:  DaemonSet/nginx-ds
Containers:
  nginx:
    Container ID:   docker://60800248d0edd65034bc5ec3a26f9c87549182ab5bca7e0eddc98f2bd07ea74b
    Image:          nginx:1.7.9
    Image ID:       docker-pullable://nginx@sha256:e3456c851a152494c3e4ff5fcc26f240206abac0c9d794affb40e0714846c451
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Tue, 13 Jun 2023 14:48:51 +0800
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-2pfll (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  kube-api-access-2pfll:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node-role.kubernetes.io/master:NoSchedule op=Exists
                             node.kubernetes.io/disk-pressure:NoSchedule op=Exists
                             node.kubernetes.io/memory-pressure:NoSchedule op=Exists
                             node.kubernetes.io/not-ready:NoExecute op=Exists
                             node.kubernetes.io/pid-pressure:NoSchedule op=Exists
                             node.kubernetes.io/unreachable:NoExecute op=Exists
                             node.kubernetes.io/unschedulable:NoSchedule op=Exists
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  80s   default-scheduler  Successfully assigned default/nginx-ds-2nx9s to kube01
  Normal  Pulling    80s   kubelet            Pulling image "nginx:1.7.9"
  Normal  Pulled     73s   kubelet            Successfully pulled image "nginx:1.7.9" in 6.478137132s
  Normal  Created    73s   kubelet            Created container nginx
  Normal  Started    73s   kubelet            Started container nginx

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