kubernetes - 如何在 statefulset 中为 kubernetes pod 设置主机名

Question

我正在使用 statefulset 并启动多个 pod，但它们不是彼此的副本。我想设置 Pod 的主机名并将这些主机名作为 env 变量传递给所有 Pod，以便它们可以相互通信。

我尝试在 pod 规范下使用主机名，但从未将主机名设置为指定的主机名。但是，它设置为主机名作为 podname-0。

# Source: testrep/templates/statefulset.yaml
apiVersion: apps/v1
kind: StatefulSet 
metadata:
  name: orbiting-butterfly-testrep
  labels:
    app.kubernetes.io/name: testrep
    helm.sh/chart: testrep-0.1.0
    app.kubernetes.io/instance: orbiting-butterfly
    app.kubernetes.io/managed-by: Tiller
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: testrep
      app.kubernetes.io/instance: orbiting-butterfly
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app.kubernetes.io/name: testrep
        app.kubernetes.io/instance: orbiting-butterfly
    spec:
      nodeSelector:
          testol: ad3
       hostname: test1
       containers:
        - name: testrep
          image: "test/database:v1"
          imagePullPolicy: IfNotPresent
          env:
           - name: DB_HOSTS
             value: test1,test2,test3

Answer 1

根据文档:

StatefulSet is the workload API object used to manage stateful applications.

Manages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods.

StatefulSet 对于需要以下一项或多项的应用程序很有值(value):

稳定、唯一的网络标识符 .

稳定、持久的存储。

有序、优雅的部署和扩展。

有序的自动滚动更新。

状态集 Limitations :

StatefulSets currently require a Headless Service to be responsible for the network identity of the Pods. You are responsible for creating this Service.

Pod Identity

StatefulSet Pods have a unique identity that is comprised of an ordinal, a stable network identity, and stable storage. The identity sticks to the Pod, regardless of which node it’s (re)scheduled on. For a StatefulSet with N replicas, each Pod in the StatefulSet will be assigned an integer ordinal, from 0 up through N-1, that is unique over the Set.

Stable Network ID

Each Pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the Pod. The pattern for the constructed hostname is $(statefulset name)-$(ordinal). The example above will create three Pods named web-0,web-1,web-2. A StatefulSet can use a Headless Service to control the domain of its Pods. The domain managed by this Service takes the form: $(service name).$(namespace).svc.cluster.local, where “cluster.local” is the cluster domain. As each Pod is created, it gets a matching DNS subdomain, taking the form: $(podname).$(governing service domain), where the governing service is defined by the serviceName field on the StatefulSet.

备注 :

您负责创建负责 Pod 网络身份的 Headless Service。

所以如 vjdhama 所述请使用 Headless Service 创建您的 Statefulset。

您可以在文档中找到此示例:

apiVersion: v1
kind: Service
metadata:
 name: nginx
 labels:
   app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx


apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  selector:
    matchLabels:
      app: nginx # has to match .spec.template.metadata.labels
  serviceName: "nginx"
  replicas: 3 # by default is 1
  template:
    metadata:
      labels:
        app: nginx # has to match .spec.selector.matchLabels
    spec:
      terminationGracePeriodSeconds: 10
      containers:
      - name: nginx
        image: k8s.gcr.io/nginx-slim:0.8
        ports:
        - containerPort: 80

在这种情况下，Pod DNS 和 Pod 主机名应分别为:

    Pod DNS
    web-{0..N-1}.nginx.default.svc.cluster.local

    Pod Hostname
    web-{0..N-1}


    NAME                                   READY   STATUS    RESTARTS   AGE     IP               
    pod/web-0                              1/1     Running   0          5m      192.168.148.78   
    pod/web-1                              1/1     Running   0          4m53s   192.168.148.79   
    pod/web-2                              1/1     Running   0          4m51s   192.168.148.80  

从 Pod 的角度:

   root@web-2:# nslookup nginx
   Server:      10.96.0.10
   Address: 10.96.0.10#53

   Name:    nginx.default.svc.cluster.local 
   Address: 192.168.148.80
   Name:    nginx.default.svc.cluster.local
   Address: 192.168.148.78
   Name:    nginx.default.svc.cluster.local
   Address: 192.168.148.79

因此，您可以使用 Pod DNS 调用每个相应的 Pod，例如:

web-0.nginx.default.svc.cluster.local

更新:

从 StatefulSet 公开单个 pod。您可以找到 here棘手的方式。
使用 Statefulset 的上述优点:

The pattern for the constructed hostname is $(statefulset name)-$(ordinal). The example above will create three Pods named web-0,web-1,web-2.

举个例子:

apiVersion: v1
kind: Service
metadata:
  name: app-0
spec:
  type: LoadBalancer
  selector:
    statefulset.kubernetes.io/pod-name: web-0
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

会为你做这件事。

希望这有帮助。