Why isn't Kubernetes service DNS working?

问题

I have set up DNS in my Kubernetes (v1.1.2+1abf20d) system, on CoreOS/AWS, but I cannot look up services via DNS. I have tried debugging, but cannot for the life of me find out why. This is what happens when I try to look up the kubernetes service, which should always be available:

$ ~/.local/bin/kubectl --kubeconfig=/etc/kubernetes/kube.conf exec busybox-sleep -- nslookup kubernetes.default
Server:    10.3.0.10
Address 1: 10.3.0.10 ip-10-3-0-10.eu-central-1.compute.internal

nslookup: can't resolve 'kubernetes.default'
error: error executing remote command: Error executing command in container: Error executing in Docker Container: 1

I have installed the DNS addon according to this spec:

apiVersion: v1
kind: ReplicationController
metadata:
  name: kube-dns-v10
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    version: v10
    kubernetes.io/cluster-service: "true"
spec:
  replicas: 1
  selector:
    k8s-app: kube-dns
    version: v10
  template:
    metadata:
      labels:
        k8s-app: kube-dns
        version: v10
        kubernetes.io/cluster-service: "true"
    spec:
      containers:
      - name: etcd
        image: gcr.io/google_containers/etcd-amd64:2.2.1
        resources:
          # keep request = limit to keep this container in guaranteed class
          limits:
            cpu: 100m
            memory: 50Mi
          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:1.12
        resources:
          # keep request = limit to keep this container in guaranteed class
          limits:
            cpu: 100m
            memory: 50Mi
          requests:
            cpu: 100m
            memory: 50Mi
        args:
        # command = "/kube2sky"
        - --domain=cluster.local
      - name: skydns
        image: gcr.io/google_containers/skydns:2015-10-13-8c72f8c
        resources:
          # keep request = limit to keep this container in guaranteed class
          limits:
            cpu: 100m
            memory: 50Mi
          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
        livenessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 30
          timeoutSeconds: 5
        readinessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 1
          timeoutSeconds: 5
      - 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.

---

apiVersion: v1
kind: Service
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    kubernetes.io/name: "KubeDNS"
spec:
  selector:
    k8s-app: kube-dns
  clusterIP: 10.3.0.10
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

Why isn't DNS lookup for services working in my Kubernetes setup? Please let me know what other info I need to provide.

回答1:

There were two things I needed to do:

1. Configure kube2sky via kubeconfig, so that it's properly configured for TLS.
2. Configure kube-proxy via kubeconfig, so that it's properly configured for TLS and finds the master node.

/etc/kubernetes/kube.conf on master node

apiVersion: v1
kind: Config
clusters:
- name: kube
  cluster:
    server: https://127.0.0.1:443
    certificate-authority: /etc/ssl/etcd/ca.pem
users:
- name: kubelet
  user:
    client-certificate: /etc/ssl/etcd/master-client.pem
    client-key: /etc/ssl/etcd/master-client-key.pem
contexts:
- context:
  cluster: kube
  user: kubelet

/etc/kubernetes/kube.conf on worker node

apiVersion: v1
kind: Config
clusters:
- name: local
  cluster:
    certificate-authority: /etc/ssl/etcd/ca.pem
    server: https://<master IP>:443
users:
- name: kubelet
  user:
    client-certificate: /etc/ssl/etcd/worker.pem
    client-key: /etc/ssl/etcd/worker-key.pem
contexts:
- context:
    cluster: local
    user: kubelet
  name: kubelet-context
current-context: kubelet-context

dns-addon.yaml (install this on master)

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
        volumeMounts:
        - name: kubernetes-etc
          mountPath: /etc/kubernetes
          readOnly: true
        - name: etcd-ssl
          mountPath: /etc/ssl/etcd
          readOnly: true
        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.
        - --kubecfg-file=/etc/kubernetes/kube.conf
      - 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: {}
      - name: kubernetes-etc
        hostPath:
          path: /etc/kubernetes
      - name: etcd-ssl
        hostPath:
          path: /etc/ssl/etcd
      dnsPolicy: Default  # Don't use cluster DNS.

/etc/kubernetes/manifests/kube-proxy.yaml on master node

apiVersion: v1
kind: Pod
metadata:
  name: kube-proxy
  namespace: kube-system
spec:
  hostNetwork: true
  containers:
  - name: kube-proxy
    image: gcr.io/google_containers/hyperkube:v1.1.2
    command:
    - /hyperkube
    - proxy
    - --master=https://127.0.0.1:443
    - --proxy-mode=iptables
    - --kubeconfig=/etc/kubernetes/kube.conf
    securityContext:
      privileged: true
    volumeMounts:
    - mountPath: /etc/ssl/certs
      name: ssl-certs-host
      readOnly: true
    - mountPath: /etc/kubernetes
      name: kubernetes
      readOnly: true
    - mountPath: /etc/ssl/etcd
      name: kubernetes-certs
      readOnly: true
  volumes:
  - hostPath:
      path: /usr/share/ca-certificates
    name: ssl-certs-host
  - hostPath:
      path: /etc/kubernetes
    name: kubernetes
  - hostPath:
      path: /etc/ssl/etcd
    name: kubernetes-certs

/etc/kubernetes/manifests/kube-proxy.yaml on worker node

apiVersion: v1
kind: Pod
metadata:
  name: kube-proxy
  namespace: kube-system
spec:
  hostNetwork: true
  containers:
  - name: kube-proxy
    image: gcr.io/google_containers/hyperkube:v1.1.2
    command:
    - /hyperkube
    - proxy
    - --kubeconfig=/etc/kubernetes/kube.conf
    - --proxy-mode=iptables
    - --v=2
    securityContext:
      privileged: true
    volumeMounts:
      - mountPath: /etc/ssl/certs
        name: "ssl-certs"
      - mountPath: /etc/kubernetes/kube.conf
        name: "kubeconfig"
        readOnly: true
      - mountPath: /etc/ssl/etcd
        name: "etc-kube-ssl"
        readOnly: true
  volumes:
    - name: "ssl-certs"
      hostPath:
        path: "/usr/share/ca-certificates"
    - name: "kubeconfig"
      hostPath:
        path: "/etc/kubernetes/kube.conf"
    - name: "etc-kube-ssl"
      hostPath:
        path: "/etc/ssl/etcd"

来源：https://stackoverflow.com/questions/35849569/why-isnt-kubernetes-service-dns-working