183 lines
6.6 KiB
Markdown
183 lines
6.6 KiB
Markdown
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## Kubernetes DNS example
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This is a toy example demonstrating how to use kubernetes DNS.
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### Step Zero: Prerequisites
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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](../../build/kube-dns/).
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```sh
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$ cd kubernetes
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$ hack/dev-build-and-up.sh
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```
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### Step One: Create two namespaces
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We'll see how cluster DNS works across multiple [namespaces](../../docs/user-guide/namespaces.md), first we need to create two namespaces:
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```sh
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$ kubectl create -f examples/cluster-dns/namespace-dev.yaml
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$ kubectl create -f examples/cluster-dns/namespace-prod.yaml
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```
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Now list all namespaces:
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```sh
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$ kubectl get namespaces
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NAME LABELS STATUS
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default <none> Active
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development name=development Active
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production name=production Active
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```
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For kubectl client to work with each namespace, we define two contexts:
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```sh
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$ kubectl config set-context dev --namespace=development --cluster=${CLUSTER_NAME} --user=${USER_NAME}
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$ kubectl config set-context prod --namespace=production --cluster=${CLUSTER_NAME} --user=${USER_NAME}
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```
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You can view your cluster name and user name in kubernetes config at ~/.kube/config.
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### Step Two: Create backend replication controller in each namespace
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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.
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```sh
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$ kubectl config use-context dev
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$ kubectl create -f examples/cluster-dns/dns-backend-rc.yaml
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```
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Once that's up you can list the pod in the cluster:
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```sh
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$ kubectl get rc
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CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
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dns-backend dns-backend ddysher/dns-backend name=dns-backend 1
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```
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Now repeat the above commands to create a replication controller in prod namespace:
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```sh
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$ kubectl config use-context prod
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$ kubectl create -f examples/cluster-dns/dns-backend-rc.yaml
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$ kubectl get rc
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CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
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dns-backend dns-backend ddysher/dns-backend name=dns-backend 1
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```
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### Step Three: Create backend service
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Use the file [`examples/cluster-dns/dns-backend-service.yaml`](dns-backend-service.yaml) to create
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a [service](../../docs/user-guide/services.md) for the backend server.
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```sh
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$ kubectl config use-context dev
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$ kubectl create -f examples/cluster-dns/dns-backend-service.yaml
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```
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Once that's up you can list the service in the cluster:
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```sh
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$ kubectl get service dns-backend
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NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
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dns-backend 10.0.2.3 <none> 8000/TCP name=dns-backend 1d
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```
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Again, repeat the same process for prod namespace:
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```sh
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$ kubectl config use-context prod
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$ kubectl create -f examples/cluster-dns/dns-backend-service.yaml
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$ kubectl get service dns-backend
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NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
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dns-backend 10.0.2.4 <none> 8000/TCP name=dns-backend 1d
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```
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### Step Four: Create client pod in one namespace
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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`.
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```sh
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$ kubectl config use-context dev
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$ kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
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```
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Once that's up you can list the pod in the cluster:
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```sh
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$ kubectl get pods dns-frontend
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NAME READY STATUS RESTARTS AGE
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dns-frontend 0/1 ExitCode:0 0 1m
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```
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Wait until the pod succeeds, then we can see the output from the client pod:
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```sh
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$ kubectl logs dns-frontend
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2015-05-07T20:13:54.147664936Z 10.0.236.129
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2015-05-07T20:13:54.147721290Z Send request to: http://dns-backend.development.cluster.local:8000
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2015-05-07T20:13:54.147733438Z <Response [200]>
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2015-05-07T20:13:54.147738295Z Hello World!
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```
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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.
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If we switch to prod namespace with the same pod config, we'll see the same result, i.e. dns will resolve across namespace.
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```sh
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$ kubectl config use-context prod
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$ kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
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$ kubectl logs dns-frontend
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2015-05-07T20:13:54.147664936Z 10.0.236.129
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2015-05-07T20:13:54.147721290Z Send request to: http://dns-backend.development.cluster.local:8000
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2015-05-07T20:13:54.147733438Z <Response [200]>
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2015-05-07T20:13:54.147738295Z Hello World!
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```
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#### Note about default namespace
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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`
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### tl; dr;
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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`.
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```sh
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# create dev and prod namespaces
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kubectl create -f examples/cluster-dns/namespace-dev.yaml
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kubectl create -f examples/cluster-dns/namespace-prod.yaml
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# create two contexts
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kubectl config set-context dev --namespace=development --cluster=${CLUSTER_NAME} --user=${USER_NAME}
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kubectl config set-context prod --namespace=production --cluster=${CLUSTER_NAME} --user=${USER_NAME}
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# create two backend replication controllers
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kubectl config use-context dev
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kubectl create -f examples/cluster-dns/dns-backend-rc.yaml
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kubectl config use-context prod
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kubectl create -f examples/cluster-dns/dns-backend-rc.yaml
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# create backend services
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kubectl config use-context dev
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kubectl create -f examples/cluster-dns/dns-backend-service.yaml
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kubectl config use-context prod
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kubectl create -f examples/cluster-dns/dns-backend-service.yaml
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# create a pod in each namespace and get its output
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kubectl config use-context dev
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kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
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kubectl logs dns-frontend
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kubectl config use-context prod
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kubectl create -f examples/cluster-dns/dns-frontend-pod.yaml
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kubectl logs dns-frontend
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```
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<!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
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[]()
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<!-- END MUNGE: GENERATED_ANALYTICS -->
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