Question

我正在尝试将一个数据库实例作为服务公开到两个Kubernetes命名空间中。在Ubuntu 16.04.1。上运行的Kubernetes版本1.11.3数据库服务是可见的，并且可以在默认名称空间中使用。我在非默认名称空间中创建了ExternalName服务，该服务引用默认名称空间中的完全限定域名，如下所示：

kind: Service
apiVersion: v1
metadata:
  name: ws-mysql
  namespace: wittlesouth
spec:
  type: ExternalName
  externalName: mysql.default.svc.cluster.local
  ports:
  - port: 3306

服务正在运行：

eric$ kubectl describe service ws-mysql --namespace=wittlesouth
Name:              ws-mysql
Namespace:         wittlesouth
Labels:            <none>
Annotations:       <none>
Selector:          <none>
Type:              ExternalName
IP:                
External Name:     mysql.default.svc.cluster.local
Port:              <unset>  3306/TCP
TargetPort:        3306/TCP
Endpoints:         <none>
Session Affinity:  None
Events:            <none>

如果我检查是否可以从在wittlesouth命名空间中运行的pod中通过名称找到该服务，则该服务名称无法解析，但是该命名空间中的其他服务（即Jira）可以：

root@rs-ws-diags-8mgqq:/# nslookup mysql.default.svc.cluster.local
Server:     10.96.0.10
Address:    10.96.0.10#53

Name:   mysql.default.svc.cluster.local
Address: 10.99.120.208

root@rs-ws-diags-8mgqq:/# nslookup ws-mysql.wittlesouth
Server:     10.96.0.10
Address:    10.96.0.10#53

*** Can't find ws-mysql.wittlesouth: No answer

root@rs-ws-diags-8mgqq:/# nslookup ws-mysql            
Server:     10.96.0.10
Address:    10.96.0.10#53

*** Can't find ws-mysql: No answer

root@rs-ws-diags-8mgqq:/# nslookup ws-mysql.wittlesouth
Server:     10.96.0.10
Address:    10.96.0.10#53

*** Can't find ws-mysql.wittlesouth: No answer

root@rs-ws-diags-8mgqq:/# nslookup ws-mysql.wittlesouth.svc.cluster.local
Server:     10.96.0.10
Address:    10.96.0.10#53

*** Can't find ws-mysql.wittlesouth.svc.cluster.local: No answer

root@rs-ws-diags-8mgqq:/# nslookup ws-mysql.wittlesouth
Server:     10.96.0.10
Address:    10.96.0.10#53

*** Can't find ws-mysql.wittlesouth: No answer

root@rs-ws-diags-8mgqq:/# nslookup jira.wittlesouth
Server:     10.96.0.10
Address:    10.96.0.10#53

Name:   jira.wittlesouth.svc.cluster.local
Address: 10.105.30.239

对这里可能存在的问题有何想法？目前，我通过更新需要使用数据库来引用在默认名称空间中运行的服务的完全限定域名的应用程序来解决此问题，但是我希望避免这种情况。我的最终目的是使命名空间具有独立的数据库实例，并希望在实际站起来第二个实例之前部署配置为可以按这种方式工作的应用程序。

Answer 1

这不适用于带有coredns和calico的Kubernetes 1.11.2。仅当您在外部运行的任何命名空间中直接引用外部服务时，它才有效：

$ kubectl get pods -n default
NAME      READY     STATUS    RESTARTS   AGE
mysql-0   2/2       Running   0          17m
mysql-1   2/2       Running   0          16m

$ kubectl get pods -n wittlesouth
NAME              READY     STATUS    RESTARTS   AGE
ricos-dummy-pod   1/1       Running   0          14s

kubectl exec -it ricos-dummy-pod -n wittlesouth bash
root@ricos-dummy-pod:/# ping mysql.default.svc.cluster.local
PING mysql.default.svc.cluster.local (192.168.1.40): 56 data bytes
64 bytes from 192.168.1.40: icmp_seq=0 ttl=62 time=0.578 ms
64 bytes from 192.168.1.40: icmp_seq=1 ttl=62 time=0.632 ms
64 bytes from 192.168.1.40: icmp_seq=2 ttl=62 time=0.628 ms
^C--- mysql.default.svc.cluster.local ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.578/0.613/0.632/0.025 ms
root@ricos-dummy-pod:/# ping ws-mysql
ping: unknown host
root@ricos-dummy-pod:/# exit

$ kubectl get svc mysql
NAME      TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
mysql     ClusterIP   None         <none>        3306/TCP   45d

$ kubectl describe svc mysql
Name:              mysql
Namespace:         default
Labels:            app=mysql
Annotations:       <none>
Selector:          app=mysql
Type:              ClusterIP
IP:                None
Port:              mysql  3306/TCP
TargetPort:        3306/TCP
Endpoints:         192.168.1.40:3306,192.168.2.25:3306
Session Affinity:  None
Events:            <none>

仅根据docs使用kube-dns支持ExternalName服务功能，而Kubernetes 1.11.x默认为coredns。您可能想要尝试从coredns更改为kube-dns，或者可能为您的coredns部署更改configs。我希望可以在某些时候使用coredns来实现。

Kubernetes ExternalName服务在DNS中不可见

1 个答案: