如何为集群外的查询公开 kube-dns 服务? [英] How to expose kube-dns service for queries outside cluster?

问题描述

我正在尝试公开kube-dns"服务，以便在 Kubernetes 集群之外进行查询.为了做到这一点，我编辑了服务"定义，将类型"从ClusterIP"更改为NodePort"，这似乎工作正常.

但是，当我尝试在节点端口上进行查询时，我能够获得 TCP 会话(使用 Telnet 进行测试)，但似乎无法从 DNS 服务器获得任何响应(使用 dig 进行测试).

我查看了kube-dns"Pod 上每个容器的日志，但没有发现任何不妥之处.此外，从集群内(从正在运行的容器)查询 DNS 似乎没有任何问题.

之前有没有人尝试过暴露 kube-dns 服务?如果是这样，是否有任何其他设置步骤或您对我有任何调试建议?

服务定义如下:

$ kubectl get service kube-dns -o yaml --namespace kube-systemapi版本:v1种类:服务元数据:...规格:集群IP:10.0.0.10端口:- 名称:DNS节点端口:31257端口:53协议:UDP目标端口:53- 名称:dns-tcp节点端口:31605端口:53协议:TCP目标端口:53选择器:k8s-app:kube-dnssessionAffinity:无类型:节点端口地位:负载均衡器:{}

解决方案

你是查询tcp端口还是udp端口?

我将 kube-dns 更改为 NodePort 服务:

$ kubectl 描述服务 kube-dns --namespace kube-system名称:kube-dns命名空间:kube-system标签:k8s-app=kube-dnskubernetes.io/cluster-service=truekubernetes.io/name=KubeDNS选择器:k8s-app=kube-dns类型:节点端口IP:10.171.240.10端口:dns 53/UDP节点端口:dns 30100/UDP端点:10.168.0.6:53端口:dns-tcp 53/TCP节点端口:dns-tcp 30490/TCP端点:10.168.0.6:53会话亲和力:无

然后从集群外部查询 udp 端口​​，一切似乎都正常:

$ dig -p 30100 @10.240.0.4 kubernetes.default.svc.cluster.local;<<>>DiG 9.9.5-9+deb8u6-Debian <<>>-p 30100 @10.240.0.4 kubernetes.default.svc.cluster.local;(找到 1 个服务器);;全局选项:+cmd;;得到答案:;;->>HEADER<<- 操作码:QUERY，状态:NOERROR，id:45472;;标志:qr aa rd ra；查询:1，答案:1，权威:0，附加:0;;问题部分:;kubernetes.default.svc.cluster.local.在一个;;回答部分:kubernetes.default.svc.cluster.local.30 中 10.171.240.1;;查询时间:3毫秒;;服务器:10.240.0.4#30100(10.240.0.4);;时间:UTC 2016 年 5 月 26 日星期四 18:27:32;;味精大小接收:70

目前，Kubernetes 不允许 NodePort 服务为 tcp & 共享相同的端口.udp(参见问题 #20092).这对于像 DNS 这样的东西来说有点时髦.

该错误已在 Kubernetes 1.3 中修复.

I'm trying to expose the "kube-dns" service to be available to be queried outside of the Kubernetes cluster. In order to do this I edited the "Service" definition to change "type" from "ClusterIP" to "NodePort" which seemed to work fine.

However, when I attempt to query on the node port, I'm able to get a TCP session (testing with Telnet) but can't seem to get any response from the DNS server (testing with dig).

I've had a look through the logs on each of the containers on the "kube-dns" Pod but can't see anything untoward. Additionally, querying the DNS from within the cluster (from a running container) appears to work without any issues.

Has anyone tried to expose the kube-dns service before? If so, are there any additional setup steps or do you have any debugging advice for me?

The service definition is as follows:

$ kubectl get service kube-dns -o yaml --namespace kube-system
apiVersion: v1
kind: Service
metadata:
...
spec:
  clusterIP: 10.0.0.10
  ports:
  - name: dns
    nodePort: 31257
    port: 53
    protocol: UDP
    targetPort: 53
  - name: dns-tcp
    nodePort: 31605
    port: 53
    protocol: TCP
    targetPort: 53
  selector:
    k8s-app: kube-dns
  sessionAffinity: None
  type: NodePort
status:
  loadBalancer: {}

解决方案

Are you querying on the tcp port or the udp port?

I changed my kube-dns to be a NodePort service:

$ kubectl describe services kube-dns --namespace kube-system
Name:           kube-dns
Namespace:      kube-system
Labels:         k8s-app=kube-dns
            kubernetes.io/cluster-service=true
            kubernetes.io/name=KubeDNS
Selector:       k8s-app=kube-dns
Type:           NodePort
IP:         10.171.240.10
Port:           dns 53/UDP
NodePort:       dns 30100/UDP
Endpoints:      10.168.0.6:53
Port:           dns-tcp 53/TCP
NodePort:       dns-tcp 30490/TCP
Endpoints:      10.168.0.6:53
Session Affinity:   None

and then queried on the udp port from outside of the cluster and everything appeared to work:

$ dig -p 30100 @10.240.0.4 kubernetes.default.svc.cluster.local

; <<>> DiG 9.9.5-9+deb8u6-Debian <<>> -p 30100 @10.240.0.4 kubernetes.default.svc.cluster.local
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45472
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;kubernetes.default.svc.cluster.local. IN A

;; ANSWER SECTION:
kubernetes.default.svc.cluster.local. 30 IN A   10.171.240.1

;; Query time: 3 msec
;; SERVER: 10.240.0.4#30100(10.240.0.4)
;; WHEN: Thu May 26 18:27:32 UTC 2016
;; MSG SIZE  rcvd: 70

Right now, Kubernetes does not allow NodePort services to share the same port for tcp & udp (see Issue #20092). That makes this a little funky for something like DNS.

EDIT: The bug was fixed in Kubernetes 1.3.

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