## Kubernetes DNS example This is a toy example demonstrating how to use kubernetes DNS. ### Step Zero: Prerequisites This example assumes that you have forked the repository and [turned up a Kubernetes cluster](../../docs/getting-started-guides/). Make sure DNS is enabled in your setup, see [DNS doc](https://github.com/kubernetes/dns). ```sh $ cd kubernetes $ hack/dev-build-and-up.sh ``` ### Step One: Create two namespaces We'll see how cluster DNS works across multiple [namespaces](../../docs/user-guide/namespaces.md), first we need to create two namespaces: ```sh $ kubectl create -f examples/cluster-dns/namespace-dev.yaml $ kubectl create -f examples/cluster-dns/namespace-prod.yaml ``` Now list all namespaces: ```sh $ kubectl get namespaces NAME LABELS STATUS default Active development name=development Active production name=production Active ``` For kubectl client to work with each namespace, we define two contexts: ```sh $ 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`](dns-backend-rc.yaml) to create a backend server [replication controller](../../docs/user-guide/replication-controller.md) in each namespace. ```sh $ 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: ```sh $ 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: ```sh $ 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`](dns-backend-service.yaml) to create a [service](../../docs/user-guide/services.md) for the backend server. ```sh $ 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: ```sh $ kubectl get service dns-backend NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE dns-backend 10.0.2.3 8000/TCP name=dns-backend 1d ``` Again, repeat the same process for prod namespace: ```sh $ kubectl config use-context prod $ kubectl create -f examples/cluster-dns/dns-backend-service.yaml $ kubectl get service dns-backend NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE dns-backend 10.0.2.4 8000/TCP name=dns-backend 1d ``` ### Step Four: Create client pod in one namespace Use the file [`examples/cluster-dns/dns-frontend-pod.yaml`](dns-frontend-pod.yaml) to create a client [pod](../../docs/user-guide/pods.md) 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`. ```sh $ 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: ```sh $ 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: ```sh $ 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 2015-05-07T20:13:54.147738295Z Hello World! ``` Please refer to the [source code](images/frontend/client.py) 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. ```sh $ 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 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.svc.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`. ```sh # 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 ``` [![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/examples/cluster-dns/README.md?pixel)]()