某些特殊情况下，需要将某些服务固定在一台宿主机上，K8S也适应这种方式，下面以mongo为例，来看看如何实现的：

kubectl label nodes kube-node node=kube-node

kubectl get node -a -l "node=kube-node"

pod或者rc的配置项中添加如下配置：

nodeSelector: 
       node: kube-node4

如mongo启动的rc文件

apiVersion: v1
kind: ReplicationController
metadata:
 name: mongo
spec:
 replicas: 1 
 template:
   metadata:
     labels:
       run: mongo
   spec:
     containers:
     - name: mongo
       image: daocloud.io/library/mongo:3.2.4
       ports:
         - containerPort: 27017
       volumeMounts:
         - mountPath: /data/db
           name: mongo
     volumes: [{"name":"mongo","hostPath":{"path":"/root/volumes/mongo"}}]
     nodeSelector: 
       node: kube-node4