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DaemonSet

DaemonSet保证在每个Node上都运行一个容器副本,常用来部署一些集群的日志、监控或者其他系统管理应用。典型的应用包括:

  • 日志收集,比如fluentd,logstash等
  • 系统监控,比如Prometheus Node Exporter,collectd,New Relic agent,Ganglia gmond等
  • 系统程序,比如kube-proxy, kube-dns, glusterd, ceph等

使用Fluentd收集日志的例子:

apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
  name: fluentd
spec:
  template:
    metadata:
      labels:
        app: logging
        id: fluentd
      name: fluentd
    spec:
      containers:
      - name: fluentd-es
        image: gcr.io/google_containers/fluentd-elasticsearch:1.3
        env:
         - name: FLUENTD_ARGS
           value: -qq
        volumeMounts:
         - name: containers
           mountPath: /var/lib/docker/containers
         - name: varlog
           mountPath: /varlog
      volumes:
         - hostPath:
             path: /var/lib/docker/containers
           name: containers
         - hostPath:
             path: /var/log
           name: varlog

指定Node节点

DaemonSet会忽略Node的unschedulable状态,有两种方式来指定Pod只运行在指定的Node节点上:

  • nodeSelector:只调度到匹配指定label的Node上
  • nodeAffinity:功能更丰富的Node选择器,比如支持集合操作
  • podAffinity:调度到满足条件的Pod所在的Node上

nodeSelector示例

首先给Node打上标签

kubectl label nodes node-01 disktype=ssd

然后在daemonset中指定nodeSelector为disktype=ssd

spec:
  nodeSelector:
    disktype: ssd

nodeAffinity示例

nodeAffinity目前支持两种:requiredDuringSchedulingIgnoredDuringExecution和preferredDuringSchedulingIgnoredDuringExecution,分别代表必须满足条件和优选条件。比如下面的例子代表调度到包含标签kubernetes.io/e2e-az-name并且值为e2e-az1或e2e-az2的Node上,并且优选还带有标签another-node-label-key=another-node-label-value的Node。

apiVersion: v1
kind: Pod
metadata:
  name: with-node-affinity
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
          - key: kubernetes.io/e2e-az-name
            operator: In
            values:
            - e2e-az1
            - e2e-az2
      preferredDuringSchedulingIgnoredDuringExecution:
      - weight: 1
        preference:
          matchExpressions:
          - key: another-node-label-key
            operator: In
            values:
            - another-node-label-value
  containers:
  - name: with-node-affinity
    image: gcr.io/google_containers/pause:2.0

podAffinity示例

podAffinity基于Pod的标签来选择Node,仅调度到满足条件Pod所在的Node上,支持podAffinity和podAntiAffinity。这个功能比较绕,以下面的例子为例:

  • 如果一个“Node所在Zone中包含至少一个带有security=S1标签且运行中的Pod”,那么可以调度到该Node
  • 不调度到“包含至少一个带有security=S2标签且运行中Pod”的Node上
apiVersion: v1
kind: Pod
metadata:
  name: with-pod-affinity
spec:
  affinity:
    podAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchExpressions:
          - key: security
            operator: In
            values:
            - S1
        topologyKey: failure-domain.beta.kubernetes.io/zone
    podAntiAffinity:
      preferredDuringSchedulingIgnoredDuringExecution:
      - weight: 100
        podAffinityTerm:
          labelSelector:
            matchExpressions:
            - key: security
              operator: In
              values:
              - S2
          topologyKey: kubernetes.io/hostname
  containers:
  - name: with-pod-affinity
    image: gcr.io/google_containers/pause:2.0

静态Pod

除了DaemonSet,还可以使用静态Pod来在每台机器上运行指定的Pod,这需要kubelet在启动的时候指定manifest目录:

kubelet --pod-manifest-path=/etc/kubernetes/manifests

然后将所需要的Pod定义文件放到指定的manifest目录中。

注意:静态Pod不能通过API Server来删除,但可以通过删除manifest文件来自动删除对应的Pod。

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