Kubernetes DNS 实例实战

译者：钟健鑫 校对：无

这是一个好玩的例子来演示如何使用kubernetes DNS

第0步: 前提条件

当前例子会假设你已经从仓库获取并启动了一个Kubernetes集群。请确保已经在设置中启动了DNS, 具体请移步DNS 文档:

$ cd kubernetes
$ hack/dev-build-and-up.sh

第一步: 创建两个namespace

接下来我们会明白集群的DNS如何在跨多个namespace的情况下工作，首先我们需要创建两个namespace:

$ kubectl create -f examples/cluster-dns/namespace-dev.yaml
$ kubectl create -f examples/cluster-dns/namespace-prod.yaml

现在我们列出所有的 namespaces:

$ kubectl get namespaces
NAME          LABELS             STATUS
default       <none>             Active
development   name=development   Active
production    name=production    Active

For kubectl client to work with each namespace, we define two contexts: 为了让kubectl客户端操作每一个不同的namespace，我们定义了两个上下文环境：

$ kubectl config set-context dev --namespace=development --cluster=${CLUSTER_NAME} --user=${USER_NAME}
$ kubectl config set-context prod --namespace=production --cluster=${CLUSTER_NAME} --user=${USER_NAME}

You can view your cluster name and user name in kubernetes config at ~/.kube/config.

Step Two: Create backend replication controller in each namespace

Use the file examples/cluster-dns/dns-backend-rc.yaml to create a backend server replication controller in each namespace.

$ kubectl config use-context dev
$ kubectl create -f examples/cluster-dns/dns-backend-rc.yaml

Once that's up you can list the pod in the cluster:

$ kubectl get rc
CONTROLLER    CONTAINER(S)   IMAGE(S)              SELECTOR           REPLICAS
dns-backend   dns-backend    ddysher/dns-backend   name=dns-backend   1

Now repeat the above commands to create a replication controller in prod namespace:

$ kubectl config use-context prod
$ kubectl create -f examples/cluster-dns/dns-backend-rc.yaml
$ kubectl get rc
CONTROLLER    CONTAINER(S)   IMAGE(S)              SELECTOR           REPLICAS
dns-backend   dns-backend    ddysher/dns-backend   name=dns-backend   1

Step Three: Create backend service

Use the file examples/cluster-dns/dns-backend-service.yaml to create a service for the backend server.

$ kubectl config use-context dev
$ kubectl create -f
examples/cluster-dns/dns-backend-service.yaml

Once that's up you can list the service in the cluster:

$ kubectl get service dns-backend
NAME          LABELS    SELECTOR           IP(S)          PORT(S)
dns-backend   <none>    name=dns-backend   10.0.236.129   8000/TCP

Again, repeat the same process for prod namespace:

$ kubectl config use-context prod
$ kubectl create -f examples/cluster-dns/dns-backend-service.yaml
$ kubectl get service dns-backend
NAME          LABELS    SELECTOR           IP(S)         PORT(S)
dns-backend   <none>    name=dns-backend   10.0.35.246   8000/TCP

Step Four: Create client pod in one namespace

Use the file examples/cluster-dns/dns-frontend-pod.yaml to create a client pod in dev namespace. The client pod will make a connection to backend and exit. Specifically, it tries to connect to address http://dns-backend.development.cluster.local:8000.

$ kubectl config use-context dev
$ kubectl create -f
examples/cluster-dns/dns-frontend-pod.yaml

Once that's up you can list the pod in the cluster:

$ kubectl get pods dns-frontend
NAME           READY     STATUS       RESTARTS   AGE
dns-frontend   0/1       ExitCode:0   0          1m

Wait until the pod succeeds, then we can see the output from the client pod:

$ kubectl logs dns-frontend
2015-05-07T20:13:54.147664936Z 10.0.236.129
2015-05-07T20:13:54.147721290Z Send request to: http://dns-backend.development.cluster.local:8000
2015-05-07T20:13:54.147733438Z <Response [200]>
2015-05-07T20:13:54.147738295Z Hello World!

Please refer to the source code about the log. First line prints out the ip address associated with the service in dev namespace; remaining lines print out our request and server response.

If we switch to prod namespace with the same pod config, we'll see the same result, i.e. dns will resolve across namespace.

$ kubectl config use-context prod
$ kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
$ kubectl logs dns-frontend
2015-05-07T20:13:54.147664936Z 10.0.236.129
2015-05-07T20:13:54.147721290Z Send request to: http://dns-backend.development.cluster.local:8000
2015-05-07T20:13:54.147733438Z <Response [200]>
2015-05-07T20:13:54.147738295Z Hello World!

Note about default namespace If you prefer not using namespace, then all your services can be addressed using default namespace, e.g. http://dns-backend.default.cluster.local:8000, or shorthand version http://dns-backend:8000

tl; dr;

For those of you who are impatient, here is the summary of the commands we ran in this tutorial. Remember to set first $CLUSTER_NAME and $USER_NAME to the values found in ~/.kube/config.

# create dev and prod namespaces
kubectl create -f examples/cluster-dns/namespace-dev.yaml
kubectl create -f examples/cluster-dns/namespace-prod.yaml

# create two contexts
kubectl config set-context dev --namespace=development --cluster=${CLUSTER_NAME} --user=${USER_NAME}
kubectl config set-context prod --namespace=production --cluster=${CLUSTER_NAME} --user=${USER_NAME}

# create two backend replication controllers
kubectl config use-context dev
kubectl create -f examples/cluster-dns/dns-backend-rc.yaml
kubectl config use-context prod
kubectl create -f examples/cluster-dns/dns-backend-rc.yaml

# create backend services
kubectl config use-context dev
kubectl create -f examples/cluster-dns/dns-backend-service.yaml
kubectl config use-context prod
kubectl create -f examples/cluster-dns/dns-backend-service.yaml

# create a pod in each namespace and get its output
kubectl config use-context dev
kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
kubectl logs dns-frontend

kubectl config use-context prod
kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
kubectl logs dns-frontend