Kubernetes的两个Service（ServiceA、ServiceB）和对应的Pod（PodA、PodB）分别属于不同的namespace名称空间，现需要PodA和PodB跨namespace名称空间并通过Service实现互访。应该如何实现？

场景需求

Kubernetes的两个Service（ServiceA、ServiceB）和对应的Pod（PodA、PodB）分别属于不同的namespace名称空间，现需要PodA和PodB跨namespace名称空间并通过Service实现互访。如何实现？

说明：这里是指通过Service的Name进行通信访问，而不是通过Service的IP【因因为每次重启Service，NAME不会改变，而IP是会改变的】。

主机配置规划

服务器名称(hostname) 系统版本 配置 内网IP 外网IP(模拟)
k8s-master CentOS7.7 2C/4G/20G 172.16.1.110 10.0.0.110
k8s-node01 CentOS7.7 2C/4G/20G 172.16.1.111 10.0.0.111
k8s-node02 CentOS7.7 2C/4G/20G 172.16.1.112 10.0.0.112

创建Service和Pod

相关yaml文件

 [root@k8s-master cross_ns]# pwd

 /root/k8s_practice/cross_ns

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# cat deply_service_myns.yaml

 apiVersion: v1

 kind: Namespace

 metadata:

   name: myns

 ---

 apiVersion: apps/v1

 kind: Deployment

 metadata:

   name: myapp-deploy1

   namespace: myns

 spec:

   replicas:

   selector:

     matchLabels:

       app: myapp

       release: v1

   template:

     metadata:

       labels:

         app: myapp

         release: v1

     spec:

       containers:

       - name: myapp

         image: registry.cn-beijing.aliyuncs.com/google_registry/myapp:v1

         imagePullPolicy: IfNotPresent

         ports:

         - name: http

           containerPort:

 ---

 apiVersion: v1

 kind: Service

 metadata:

   name: myapp-clusterip1

   namespace: myns

 spec:

   type: ClusterIP  # 默认类型

   selector:

     app: myapp

     release: v1

   ports:

   - name: http

     port:

     targetPort: 

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# cat deply_service_mytest.yaml

 apiVersion: v1

 kind: Namespace

 metadata:

   name: mytest

 ---

 apiVersion: apps/v1

 kind: Deployment

 metadata:

   name: myapp-deploy2

   namespace: mytest

 spec:

   replicas:

   selector:

     matchLabels:

       app: myapp

       release: v2

   template:

     metadata:

       labels:

         app: myapp

         release: v2

     spec:

       containers:

       - name: myapp

         image: registry.cn-beijing.aliyuncs.com/google_registry/myapp:v2

         imagePullPolicy: IfNotPresent

         ports:

         - name: http

           containerPort:

 ---

 apiVersion: v1

 kind: Service

 metadata:

   name: myapp-clusterip2

   namespace: mytest

 spec:

   type: ClusterIP  # 默认类型

   selector:

     app: myapp

     release: v2

   ports:

   - name: http

     port:

     targetPort:

运行yaml文件

 kubectl apply -f deply_service_myns.yaml

 kubectl apply -f deply_service_mytest.yaml

查看myns名称空间信息

 [root@k8s-master cross_ns]# kubectl get svc -n myns -o wide

 NAME               TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE   SELECTOR

 myapp-clusterip1   ClusterIP   10.100.61.11   <none>        /TCP    3m    app=myapp,release=v1

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get deploy -n myns -o wide

 NAME            READY   UP-TO-DATE   AVAILABLE   AGE    CONTAINERS   IMAGES                                                      SELECTOR

 myapp-deploy1   /                            3m7s   myapp        registry.cn-beijing.aliyuncs.com/google_registry/myapp:v1   app=myapp,release=v1

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get rs -n myns -o wide

 NAME                       DESIRED   CURRENT   READY   AGE     CONTAINERS   IMAGES                                                      SELECTOR

 myapp-deploy1-5b9d78576c                            3m15s   myapp        registry.cn-beijing.aliyuncs.com/google_registry/myapp:v1   app=myapp,pod-template-hash=5b9d78576c,release=v1

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get pod -n myns -o wide

 NAME                             READY   STATUS    RESTARTS   AGE     IP             NODE         NOMINATED NODE   READINESS GATES

 myapp-deploy1-5b9d78576c-wfw4n   /     Running             3m20s   10.244.2.136   k8s-node02   <none>           <none>

 myapp-deploy1-5b9d78576c-zsfjl   /     Running             3m20s   10.244.3.193   k8s-node01   <none>           <none>

查看mytest名称空间信息

 [root@k8s-master cross_ns]# kubectl get svc -n mytest -o wide

 NAME               TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE    SELECTOR

 myapp-clusterip2   ClusterIP   10.100.201.103   <none>        /TCP    4m9s   app=myapp,release=v2

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get deploy -n mytest -o wide

 NAME            READY   UP-TO-DATE   AVAILABLE   AGE     CONTAINERS   IMAGES                                                      SELECTOR

 myapp-deploy2   /                            4m15s   myapp        registry.cn-beijing.aliyuncs.com/google_registry/myapp:v2   app=myapp,release=v2

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get rs -n mytest -o wide

 NAME                      DESIRED   CURRENT   READY   AGE     CONTAINERS   IMAGES                                                      SELECTOR

 myapp-deploy2-dc8f96497                            4m22s   myapp        registry.cn-beijing.aliyuncs.com/google_registry/myapp:v2   app=myapp,pod-template-hash=dc8f96497,release=v2

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get pod -n mytest -o wide

 NAME                            READY   STATUS    RESTARTS   AGE     IP             NODE         NOMINATED NODE   READINESS GATES

 myapp-deploy2-dc8f96497-nnkqn   /     Running             4m27s   10.244.3.194   k8s-node01   <none>           <none>

 myapp-deploy2-dc8f96497-w47dt   /     Running             4m27s   10.244.2.137   k8s-node02   <none>           <none>

只看Service和Pod

 [root@k8s-master cross_ns]# kubectl get pod -A -o wide | grep -E '(my)|(NAME)'

 NAMESPACE              NAME                                         READY   STATUS    RESTARTS   AGE   IP             NODE         NOMINATED NODE   READINESS GATES

 myns                   myapp-deploy1-5b9d78576c-wfw4n               /     Running             41m   10.244.2.136   k8s-node02   <none>           <none>

 myns                   myapp-deploy1-5b9d78576c-zsfjl               /     Running             41m   10.244.3.193   k8s-node01   <none>           <none>

 mytest                 myapp-deploy2-dc8f96497-nnkqn                /     Running             41m   10.244.3.194   k8s-node01   <none>           <none>

 mytest                 myapp-deploy2-dc8f96497-w47dt                /     Running             41m   10.244.2.137   k8s-node02   <none>           <none>

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get svc -A -o wide | grep -E '(my)|(NAME)'

 NAMESPACE              NAME                        TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)                  AGE   SELECTOR

 myns                   myapp-clusterip1            ClusterIP   10.100.61.11     <none>        /TCP                   41m   app=myapp,release=v1

 mytest                 myapp-clusterip2            ClusterIP   10.100.201.103   <none>        /TCP                   41m   app=myapp,release=v2

pod跨名称空间namespace与Service通信

说明：是通过Service的NAME进行通信，而不是Service的IP【因为每次重启Service，NAME不会改变，而IP是会改变的】。

 # 进入ns名称空间下的一个Pod容器

 [root@k8s-master cross_ns]# kubectl exec -it -n myns myapp-deploy1-5b9d78576c-wfw4n sh

 / # cd /root/

 ### 如下说明在同一名称空间下，通信无问题

 ~ # ping myapp-clusterip1

 PING myapp-clusterip1 (10.100.61.11):  data bytes

  bytes from 10.100.61.11: seq= ttl= time=0.046 ms

  bytes from 10.100.61.11: seq= ttl= time=0.081 ms

 ~ #

 ~ # wget myapp-clusterip1 -O myns.html

 Connecting to myapp-clusterip1 (10.100.61.11:)

 myns.html            %

 ~ #

 ~ # cat myns.html

 Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>

 ### 如下说明在不同的名称空间下，通过Service的NAME进行通信存在问题

 ~ # ping myapp-clusterip2

 ping: bad address 'myapp-clusterip2'

 ~ #

 ~ # wget myapp-clusterip2 -O mytest.html

 wget: bad address 'myapp-clusterip2'

实现跨namespace与Service通信

通过Service的ExternalName类型即可实现跨namespace名称空间与Service通信。

Service域名格式：$(service name).$(namespace).svc.cluster.local，其中 cluster.local 为指定的集群的域名

相关yaml文件

 [root@k8s-master cross_ns]# pwd

 /root/k8s_practice/cross_ns

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# cat svc_ExternalName_visit.yaml

 # 实现 myns 名称空间的pod，访问 mytest 名称空间的Service：myapp-clusterip2

 apiVersion: v1

 kind: Service

 metadata:

   name: myapp-clusterip1-externalname

   namespace: myns

 spec:

   type: ExternalName

   externalName: myapp-clusterip2.mytest.svc.cluster.local

   ports:

   - name: http

     port:

     targetPort:

 ---

 # 实现 mytest 名称空间的Pod，访问 myns 名称空间的Service：myapp-clusterip1

 apiVersion: v1

 kind: Service

 metadata:

   name: myapp-clusterip2-externalname

   namespace: mytest

 spec:

   type: ExternalName

   externalName: myapp-clusterip1.myns.svc.cluster.local

   ports:

   - name: http

     port:

     targetPort:

运行yaml文件

 [root@k8s-master cross_ns]# kubectl apply -f svc_ExternalName_visit.yaml

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get svc -A -o wide | grep -E '(ExternalName)|(NAME)'

 NAMESPACE              NAME                            TYPE           CLUSTER-IP       EXTERNAL-IP                                 PORT(S)                  AGE   SELECTOR

 myns                   myapp-clusterip1-externalname   ExternalName   <none>           myapp-clusterip2.mytest.svc.cluster.local   /TCP                   28s   <none>

 mytest                 myapp-clusterip2-externalname   ExternalName   <none>           myapp-clusterip1.myns.svc.cluster.local     /TCP                   28s   <none>

pod跨名称空间namespace与Service通信

到目前所有service和pod信息查看

 [root@k8s-master cross_ns]# kubectl get svc -A -o wide | grep -E '(my)|(NAME)'

 NAMESPACE              NAME                            TYPE           CLUSTER-IP       EXTERNAL-IP                                 PORT(S)                  AGE   SELECTOR

 myns                   myapp-clusterip1                ClusterIP      10.100.61.11     <none>                                      /TCP                   62m   app=myapp,release=v1

 myns                   myapp-clusterip1-externalname   ExternalName   <none>           myapp-clusterip2.mytest.svc.cluster.local   /TCP                   84s   <none>

 mytest                 myapp-clusterip2                ClusterIP      10.100.201.103   <none>                                      /TCP                   62m   app=myapp,release=v2

 mytest                 myapp-clusterip2-externalname   ExternalName   <none>           myapp-clusterip1.myns.svc.cluster.local     /TCP                   84s   <none>

 [root@k8s-master cross_ns]#

 [root@k8s-master cross_ns]# kubectl get pod -A -o wide | grep -E '(my)|(NAME)'

 NAMESPACE              NAME                                         READY   STATUS    RESTARTS   AGE   IP             NODE         NOMINATED NODE   READINESS GATES

 myns                   myapp-deploy1-5b9d78576c-wfw4n               /     Running             62m   10.244.2.136   k8s-node02   <none>           <none>

 myns                   myapp-deploy1-5b9d78576c-zsfjl               /     Running             62m   10.244.3.193   k8s-node01   <none>           <none>

 mytest                 myapp-deploy2-dc8f96497-nnkqn                /     Running             62m   10.244.3.194   k8s-node01   <none>           <none>

 mytest                 myapp-deploy2-dc8f96497-w47dt                /     Running             62m   10.244.2.137   k8s-node02   <none>           <none>

myns 名称空间的pod，访问 mytest 名称空间的Service：myapp-clusterip2

 [root@k8s-master cross_ns]# kubectl exec -it -n myns myapp-deploy1-5b9d78576c-wfw4n sh

 / # cd /root/

 ### 如下说明在同一名称空间下，通信无问题

 ~ # ping myapp-clusterip1

 PING myapp-clusterip1 (10.100.61.11):  data bytes

  bytes from 10.100.61.11: seq= ttl= time=0.057 ms

  bytes from 10.100.61.11: seq= ttl= time=0.071 ms

 ………………

 ~ #

 ~ # wget myapp-clusterip1 -O myns.html

 Connecting to myapp-clusterip1 (10.100.61.11:)

 myns.html            %

 ~ #

 ~ # cat myns.html

 Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>

 ### 如下说明通过Service externalname类型，实现了Pod跨namespace名称空间与Service访问

 ~ # ping myapp-clusterip1-externalname

 PING myapp-clusterip1-externalname (10.100.201.103):  data bytes

  bytes from 10.100.201.103: seq= ttl= time=0.050 ms

  bytes from 10.100.201.103: seq= ttl= time=0.311 ms

 ………………

 ~ #

 ~ # wget myapp-clusterip1-externalname -O mytest.html

 Connecting to myapp-clusterip1-externalname (10.100.201.103:)

 mytest.html          %

 ~ #

 ~ # cat mytest.html

 Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>

mytest 名称空间的Pod，访问 myns 名称空间的Service：myapp-clusterip1

 [root@k8s-master cross_ns]# kubectl exec -it -n mytest myapp-deploy2-dc8f96497-w47dt sh

 / # cd /root/

 ### 如下说明在同一名称空间下，通信无问题

 ~ # ping myapp-clusterip2

 PING myapp-clusterip2 (10.100.201.103):  data bytes

  bytes from 10.100.201.103: seq= ttl= time=0.087 ms

  bytes from 10.100.201.103: seq= ttl= time=0.073 ms

 ………………

 ~ #

 ~ # wget myapp-clusterip2 -O mytest.html

 Connecting to myapp-clusterip2 (10.100.201.103:)

 mytest.html          %

 ~ #

 ~ # cat mytest.html

 Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>

 ### 如下说明通过Service externalname类型，实现了Pod跨namespace名称空间与Service访问

 ~ # ping myapp-clusterip2-externalname

 PING myapp-clusterip2-externalname (10.100.61.11):  data bytes

  bytes from 10.100.61.11: seq= ttl= time=0.089 ms

  bytes from 10.100.61.11: seq= ttl= time=0.071 ms

 ………………

 ~ #

 ~ # wget myapp-clusterip2-externalname -O myns.html

 Connecting to myapp-clusterip2-externalname (10.100.61.11:)

 myns.html            %

 ~ #

 ~ # cat myns.html

 Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>

由上可见，实现了Pod跨namespace名称空间与Service访问。

完毕！

———END———
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