我正在尝试在 Centos 7 上的 Kubernetes 1.2 中设置 DNS 支持。根据文档，有两种方法可以做到这一点。第一个适用于“支持的 kubernetes 集群设置”并涉及设置环境变量：
ENABLE_CLUSTER_DNS="${KUBE_ENABLE_CLUSTER_DNS:-true}"
DNS_SERVER_IP="10.0.0.10"
DNS_DOMAIN="cluster.local"
DNS_REPLICAS=1
我将这些设置添加到 /etc/kubernetes/config 并重新启动，但没有任何效果，所以要么我没有受支持的 kubernetes 集群设置（那是什么？），要么需要其他一些东西来设置它的环境。
第二种方法需要更多的手动设置。它向 kubelet 添加了两个标志，我通过更新 /etc/kubernetes/kubelet 来设置它们以包括：
KUBELET_ARGS="--cluster-dns=10.0.0.10 --cluster-domain=cluster.local"
并使用 重新启动 kubelet systemctl restart kubelet。然后有必要启动一个复制控制器和一个服务。上面引用的文档页面为此提供了几个模板文件，需要进行一些编辑，都用于本地更改（我的 Kubernetes API 服务器侦听主机名的实际 IP 地址而不是 127.0.0.1，因此有必要添加一个 -- kube-master-url 设置）并删除一些 Salt 依赖项。当我这样做时，复制控制器成功启动了四个容器，但 kube2sky 容器在完成初始化大约一分钟后终止：
[david@centos dns]$ kubectl --server="http://centos:8080" --namespace="kube-system" logs -f kube-dns-v11-t7nlb -c kube2sky
I0325 20:58:18.516905 1 kube2sky.go:462] Etcd server found: http://127.0.0.1:4001
I0325 20:58:19.518337 1 kube2sky.go:529] Using http://192.168.87.159:8080 for kubernetes master
I0325 20:58:19.518364 1 kube2sky.go:530] Using kubernetes API v1
I0325 20:58:19.518468 1 kube2sky.go:598] Waiting for service: default/kubernetes
I0325 20:58:19.533597 1 kube2sky.go:660] Successfully added DNS record for Kubernetes service.
F0325 20:59:25.698507 1 kube2sky.go:625] Received signal terminated
我已经确定终止是由 healthz 容器在报告后完成的：
2016/03/25 21:00:35 Client ip 172.17.42.1:58939 requesting /healthz probe servicing cmd nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
2016/03/25 21:00:35 Healthz probe error: Result of last exec: nslookup: can't resolve 'kubernetes.default.svc.cluster.local', at 2016-03-25 21:00:35.608106622 +0000 UTC, error exit status 1
除此之外，所有其他日志看起来都正常。但是，有一个异常情况：在创建复制控制器时必须指定 --validate=false，否则该命令会收到以下消息：
error validating "skydns-rc.yaml": error validating data: [found invalid field successThreshold for v1.Probe, found invalid field failureThreshold for v1.Probe]; if you choose to ignore these errors, turn validation off with --validate=false
这可能有关系吗？这些论点直接来自 Kubernetes 文档。如果没有，需要什么来运行它？
这是我使用的skydns-rc.yaml：
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"
- --kube-master-url=http://192.168.87.159:8080
- 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.
和skydns-svc.yaml：
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: "10.0.0.10"
ports:
- name: dns
port: 53
protocol: UDP
- name: dns-tcp
port: 53
protocol: TCP