DaemonSet控制器是用于保证在集群上精确运行的负载有多少个实例，如有10个节点那么其就会在每个节点上只运行一个。

DaemonSet可以实现在集群内所有节点上只运行一个，也可以在集群内拥有某个标签的节点上运行一个。

DaemonSet可以简称为DS.

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# 获取当前系统上kube-system名称空间下的ds资源
root@k8s-master01:~/yaml/chapter08# kubectl get ds -n kube-system
NAME              DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR            AGE
kube-flannel-ds   4         4         4       4            4           <none>                   6d23h
kube-proxy        4         4         4       4            4           kubernetes.io/os=linux   6d23h

DaemonSet资源定义规范

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apiVersion: apps/v1  # API群组及版本
kind: DaemonSet  # 资源类型特有标识
metadata:
  name <string>  # 资源名称，在作用域中要唯一
  namespace <string>  # 名称空间；DaemonSet资源隶属名称空间级别
spec:
  minReadySeconds <integer>  # Pod就绪后多少秒内任一容器无crash方可视为“就绪”
  selector <object> # 标签选择器，必须匹配template字段中Pod模板中的标签
  template <object>  # Pod模板对象；
  revisionHistoryLimit <integer> # 滚动更新历史记录数量，默认为10；
  updateStrategy <Object> # 滚动更新策略
    type <string>  # 滚动更新类型，可用值有OnDelete和RollingUpdate；
    rollingUpdate <Object>  # 滚动更新参数，专用于RollingUpdate类型
      maxUnavailable <string>  # 更新期间可比期望的Pod数量缺少的数量或比例

DaemonSet示例

1.编写资源清单

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root@k8s-master01:~/yaml/chapter08# vim daemonset-demo.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: daemonset-demo
  namespace: default
  labels:
    app: prometheus
    component: node-exporter
spec:
  selector:
    matchLabels:
      app: prometheus
      component: node-exporter
  template:
    metadata:
      name: prometheus-node-exporter
      labels:
        app: prometheus
        component: node-exporter
    spec:
      containers:
      - name: promethous-node-exporter
        image: prom/node-exporter:v0.18.0
        ports:
        - name: prom-node-exp
          containerPort: 9100
          hostPort: 9100
        livenessProbe:
          tcpSocket:
            port: prom-node-exp
          initialDelaySeconds: 3
        readinessProbe:
          httpGet:
            path: '/metrics'
            port: prom-node-exp
            scheme: HTTP
          initialDelaySeconds: 5
      hostNetwork: true
      hostPID: true

2.应用配置清单

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root@k8s-master01:~/yaml/chapter08# kubectl apply -f daemonset-demo.yaml
daemonset.apps/daemonset-demo created

root@k8s-master01:~/yaml/chapter08# kubectl get pods -l 'app=prometheus' -o wide
NAME                   READY   STATUS    RESTARTS   AGE    IP             NODE         NOMINATED NODE   READINESS GATES
daemonset-demo-6qqmt   1/1     Running   0          4m5s   172.16.11.81   k8s-node01   <none>           <none>
daemonset-demo-fvkhj   1/1     Running   0          4m5s   172.16.11.83   k8s-node03   <none>           <none>
daemonset-demo-pxmrd   1/1     Running   0          4m5s   172.16.11.82   k8s-node02   <none>           <none>
# 已经在每个node节点部署上了

3.测试访问

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root@k8s-master01:~/yaml/chapter08# curl 172.16.11.81:9100/metrics
# HELP go_gc_duration_seconds A summary of the GC invocation durations.
# TYPE go_gc_duration_seconds summary
go_gc_duration_seconds{quantile="0"} 3.5862e-05
go_gc_duration_seconds{quantile="0.25"} 9.0353e-05
go_gc_duration_seconds{quantile="0.5"} 0.000111509
go_gc_duration_seconds{quantile="0.75"} 0.000156903
go_gc_duration_seconds{quantile="1"} 0.003124382
go_gc_duration_seconds_sum 0.006404565
go_gc_duration_seconds_count 25
# HELP go_goroutines Number of goroutines that currently exist.
# TYPE go_goroutines gauge
go_goroutines 6
# HELP go_info Information about the Go environment.
# TYPE go_info gauge
go_info{version="go1.12.5"} 1
# HELP go_memstats_alloc_bytes Number of bytes allocated and still in use.
# TYPE go_memstats_alloc_bytes gauge
go_memstats_alloc_bytes 2.99224e+06
# HELP go_memstats_alloc_bytes_total Total number of bytes allocated, even if freed.
# TYPE go_memstats_alloc_bytes_total counter
go_memstats_alloc_bytes_total 6.2666904e+07
# HELP go_memstats_buck_hash_sys_bytes Number of bytes used by the profiling bucket hash table.
# TYPE go_memstats_buck_hash_sys_bytes gauge
go_memstats_buck_hash_sys_bytes 1.465696e+06