kubernetes skydns未能转发请求

Question

我正在创建一个由1个主节点组成的集群，2节点是kubernetes。我正在尝试创建基于以下内容的天窗：

apiVersion: v1
kind: ReplicationController
metadata:
  name: kube-dns-v11
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    version: v11
    kubernetes.io/cluster-service: "true"
spec:
  replicas: 1
  selector:
    k8s-app: kube-dns
    version: v11
  template:
    metadata:
      labels:
        k8s-app: kube-dns
        version: v11
        kubernetes.io/cluster-service: "true"
    spec:
      containers:
      - name: etcd
        image: gcr.io/google_containers/etcd-amd64:2.2.1
        # resources:
        #   # TODO: Set memory limits when we've profiled the container for large
        #   # clusters, then set request = limit to keep this container in
        #   # guaranteed class. Currently, this container falls into the
        #   # "burstable" category so the kubelet doesn't backoff from restarting it.
        #   limits:
        #     cpu: 100m
        #     memory: 500Mi
        #   requests:
        #     cpu: 100m
        #     memory: 50Mi
        command:
        - /usr/local/bin/etcd
        - -data-dir
        - /var/etcd/data
        - -listen-client-urls
        - http://127.0.0.1:2379,http://127.0.0.1:4001
        - -advertise-client-urls
        - http://127.0.0.1:2379,http://127.0.0.1:4001
        - -initial-cluster-token
        - skydns-etcd
        volumeMounts:
        - name: etcd-storage
          mountPath: /var/etcd/data
      - name: kube2sky
        image: gcr.io/google_containers/kube2sky:1.14
        # resources:
        #   # TODO: Set memory limits when we've profiled the container for large
        #   # clusters, then set request = limit to keep this container in
        #   # guaranteed class. Currently, this container falls into the
        #   # "burstable" category so the kubelet doesn't backoff from restarting it.
        #   limits:
        #     cpu: 100m
        #     # Kube2sky watches all pods.
        #     memory: 200Mi
        #   requests:
        #     cpu: 100m
        #     memory: 50Mi
        livenessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          # successThreshold: 1
          # failureThreshold: 5
        readinessProbe:
          httpGet:
            path: /readiness
            port: 8081
            scheme: HTTP
          # we poll on pod startup for the Kubernetes master service and
          # only setup the /readiness HTTP server once that's available.
          initialDelaySeconds: 30
          timeoutSeconds: 5
        args:
        # command = "/kube2sky"
        - --domain=cluster.local
      - name: skydns
        image: gcr.io/google_containers/skydns:2015-10-13-8c72f8c
        resources:
          # TODO: Set memory limits when we've profiled the container for large
          # clusters, then set request = limit to keep this container in
          # guaranteed class. Currently, this container falls into the
          # "burstable" category so the kubelet doesn't backoff from restarting it.
          limits:
            cpu: 100m
            memory: 200Mi
          requests:
            cpu: 100m
            memory: 50Mi
        args:
        # command = "/skydns"
        - -machines=http://127.0.0.1:4001
        - -addr=0.0.0.0:53
        - -ns-rotate=false
        - -domain=cluster.local
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
      - name: healthz
        image: gcr.io/google_containers/exechealthz:1.0
        # resources:
        #   # keep request = limit to keep this container in guaranteed class
        #   limits:
        #     cpu: 10m
        #     memory: 20Mi
        #   requests:
        #     cpu: 10m
        #     memory: 20Mi
        args:
        - -cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
        - -port=8080
        ports:
        - containerPort: 8080
          protocol: TCP
      volumes:
      - name: etcd-storage
        emptyDir: {}
      dnsPolicy: Default  # Don't use cluster DNS.

然而，天空正在吐出以下东西：

> $kubectl logs kube-dns-v11-k07j9 --namespace=kube-system  skydns 
> 2016/04/18 12:47:05 skydns: falling back to default configuration,
> could not read from etcd: 100: Key not found (/skydns) [1]  2016/04/18
> 12:47:05 skydns: ready for queries on cluster.local. for
> tcp://0.0.0.0:53 [rcache 0]  2016/04/18 12:47:05 skydns: ready for
> queries on cluster.local. for udp://0.0.0.0:53 [rcache 0]  2016/04/18
> 12:47:11 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:47:15 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout" 2016/04/18
> 12:47:19 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:47:23 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout" 2016/04/18
> 12:47:27 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:47:31 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout" 2016/04/18
> 12:47:35 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:47:39 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout" 2016/04/18
> 12:47:43 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:47:47 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout" 2016/04/18
> 12:47:51 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:47:55 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout" 2016/04/18
> 12:47:59 skydns: failure to forward request "read udp
>     192.168.122.1:53: i/o timeout" 2016/04/18 12:48:03 skydns: failure to forward request "read udp 192.168.122.1:53: i/o timeout"

再看一看，我才意识到什么是192.168.122.1？它是kvm上的虚拟开关。为什么skydns试图访问我的虚拟交换机或虚拟机的dns服务器？

Answer 1

SkyDNS将其转发名称服务器默认为/etc/resolv.conf中列出的名称服务器。由于SkyDNS作为集群插件在kube-dns荚中运行，因此它从主机继承/etc/resolv.conf，如 doc中所述。

从您的问题来看，您的主机的/etc/resolv.conf被配置为使用192.168.122.1作为其名称服务器，从而成为SkyDNS配置中的转发服务器。我认为192.168.122.1不能从您的Kubernetes集群中路由，这就是为什么您在kube-dns日志中看到“未能转发请求”错误的原因。

解决此问题的最简单方法是向RC配置中的SkyDNS提供一个可访问的DNS服务器作为标志。下面是一个示例(它只是您的RC配置，但在SkyDNS容器规范中添加了SkyDNS标志)：

apiVersion: v1
kind: ReplicationController
metadata:
  name: kube-dns-v11
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    version: v11
    kubernetes.io/cluster-service: "true"
spec:
  replicas: 1
  selector:
    k8s-app: kube-dns
    version: v11
  template:
    metadata:
      labels:
        k8s-app: kube-dns
        version: v11
        kubernetes.io/cluster-service: "true"
    spec:
      containers:
      - name: etcd
        image: gcr.io/google_containers/etcd-amd64:2.2.1
        # resources:
        #   # TODO: Set memory limits when we've profiled the container for large
        #   # clusters, then set request = limit to keep this container in
        #   # guaranteed class. Currently, this container falls into the
        #   # "burstable" category so the kubelet doesn't backoff from restarting it.
        #   limits:
        #     cpu: 100m
        #     memory: 500Mi
        #   requests:
        #     cpu: 100m
        #     memory: 50Mi
        command:
        - /usr/local/bin/etcd
        - -data-dir
        - /var/etcd/data
        - -listen-client-urls
        - http://127.0.0.1:2379,http://127.0.0.1:4001
        - -advertise-client-urls
        - http://127.0.0.1:2379,http://127.0.0.1:4001
        - -initial-cluster-token
        - skydns-etcd
        volumeMounts:
        - name: etcd-storage
          mountPath: /var/etcd/data
      - name: kube2sky
        image: gcr.io/google_containers/kube2sky:1.14
        # resources:
        #   # TODO: Set memory limits when we've profiled the container for large
        #   # clusters, then set request = limit to keep this container in
        #   # guaranteed class. Currently, this container falls into the
        #   # "burstable" category so the kubelet doesn't backoff from restarting it.
        #   limits:
        #     cpu: 100m
        #     # Kube2sky watches all pods.
        #     memory: 200Mi
        #   requests:
        #     cpu: 100m
        #     memory: 50Mi
        livenessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          # successThreshold: 1
          # failureThreshold: 5
        readinessProbe:
          httpGet:
            path: /readiness
            port: 8081
            scheme: HTTP
          # we poll on pod startup for the Kubernetes master service and
          # only setup the /readiness HTTP server once that's available.
          initialDelaySeconds: 30
          timeoutSeconds: 5
        args:
        # command = "/kube2sky"
        - --domain=cluster.local
      - name: skydns
        image: gcr.io/google_containers/skydns:2015-10-13-8c72f8c
        resources:
          # TODO: Set memory limits when we've profiled the container for large
          # clusters, then set request = limit to keep this container in
          # guaranteed class. Currently, this container falls into the
          # "burstable" category so the kubelet doesn't backoff from restarting it.
          limits:
            cpu: 100m
            memory: 200Mi
          requests:
            cpu: 100m
            memory: 50Mi
        args:
        # command = "/skydns"
        - -machines=http://127.0.0.1:4001
        - -addr=0.0.0.0:53
        - -ns-rotate=false
        - -domain=cluster.local
        - -nameservers=8.8.8.8:53,8.8.4.4:53  # Adding this flag. Dont use double quotes.
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
      - name: healthz
        image: gcr.io/google_containers/exechealthz:1.0
        # resources:
        #   # keep request = limit to keep this container in guaranteed class
        #   limits:
        #     cpu: 10m
        #     memory: 20Mi
        #   requests:
        #     cpu: 10m
        #     memory: 20Mi
        args:
        - -cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
        - -port=8080
        ports:
        - containerPort: 8080
          protocol: TCP
      volumes:
      - name: etcd-storage
        emptyDir: {}
      dnsPolicy: Default  # Don't use cluster DNS.