6. Networking (13%)

1. Routing Traffic to Pods from Inside and Outside of a Cluster

Create a deployment named myapp that creates 2 replicas for Pods with the image nginx. Expose the container port 80.
Expose the Pods so that requests can be made against the service from inside of the cluster.
Create a temporary Pods using the image busybox and run a wget command against the IP of the service.
Change the service type so that the Pods can be reached from outside of the cluster.
Run a wget command against the service from outside of the cluster.
(Optional) Can you expose the Pods as a service without a deployment?

答案： Create a deployment with 2 replicas first. You should end up with one deployment and two Pods. 参考官网：deployment

$ kubectl run myapp --image=nginx --restart=Always --replicas=2 --port=80
deployment.apps/myapp created
$ kubectl get deployments,pods
NAME                          DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
deployment.extensions/myapp   2         2         2            2           59s

NAME                         READY   STATUS    RESTARTS   AGE
pod/myapp-7bc568bfdd-972wg   1/1     Running   0          59s
pod/myapp-7bc568bfdd-l5nmz   1/1     Running   0          59s

Expose the service with the type ClusterIP and the target port 80.

$ kubectl expose deploy myapp --target-port=80
service/myapp exposed
$ kubectl get services
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
myapp        ClusterIP   10.108.88.208   <none>        80/TCP    15s

Determine the cluster IP and use it for the wget command.

$ kubectl run tmp --image=busybox --restart=Never -it --rm -- wget -O- 10.108.88.208:80
Connecting to 10.108.88.208:80 (10.108.88.208:80)
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>
-                    100% |********************************|   612  0:00:00 ETA
pod "tmp" deleted

Turn the type of the service into NodePort to expose it outside of the cluster. Now, the service should expose a port in the 30000 range.

$ kubectl edit service myapp
...
spec:
  type: NodePort
...

kubectl get services
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
myapp        NodePort    10.108.88.208   <none>        80:30441/TCP   3m

Run a wget or curl command against the service using port 30441. On Docker for Windows/Mac you may have to use localhost or 127.0.0.1 (see issue).

$ wget -O- localhost:30441
--2019-05-10 16:32:35--  http://localhost:30441/
Resolving localhost (localhost)... ::1, 127.0.0.1
Connecting to localhost (localhost)|::1|:30441... connected.
HTTP request sent, awaiting response... 200 OK
Length: 612 [text/html]
Saving to: ‘STDOUT’

-                                          0%[                                                                                   ]       0  --.-KB/s               <!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>
-                                        100%[==================================================================================>]     612  --.-KB/s    in 0s

2019-05-10 16:32:35 (24.3 MB/s) - written to stdout [612/612]

Restricting Access to and from a Pod

Let’s assume we are working on an application stack that defines three different layers: a frontend, a backend and a database. Each of the layers runs in a Pod. You can find the definition in the YAML file app-stack.yaml. The application needs to run in the namespace app-stack.

kind: Pod
apiVersion: v1
metadata:
  name: frontend
  namespace: app-stack
  labels:
    app: todo
    tier: frontend
spec:
  containers:
    - name: frontend
      image: nginx

---

kind: Pod
apiVersion: v1
metadata:
  name: backend
  namespace: app-stack
  labels:
    app: todo
    tier: backend
spec:
  containers:
    - name: backend
      image: nginx

---

kind: Pod
apiVersion: v1
metadata:
  name: database
  namespace: app-stack
  labels:
    app: todo
    tier: database
spec:
  containers:
    - name: database
      image: mysql
      env:
      - name: MYSQL_ROOT_PASSWORD
        value: example

任务：

Create the required namespace.
Copy the Pod definition to the file app-stack.yaml and create all three Pods. Notice that the namespace has already been defined in the YAML definition.
Create a network policy in the YAML file app-stack-network-policy.yaml.
The network policy should allow incoming traffic from the backend to the database but disallow incoming traffic from the frontend.
Incoming traffic to the database should only be allowed on TCP port 3306 and no other port.

参考官网：networkpolicy Create the namespace

$ kubectl create namespace app-stack
namespace/app-stack created

$ vim app-stack.yaml
$ kubectl create -f app-stack.yaml
pod/frontend created
pod/backend created
pod/database created

$ kubectl get pods --namespace app-stack
NAME       READY   STATUS    RESTARTS   AGE
backend    1/1     Running   0          22s
database   1/1     Running   0          22s
frontend   1/1     Running   0          22s

The following definition ensure that all rules are fulfilled.

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: app-stack-network-policy
  namespace: app-stack
spec:
  podSelector:
    matchLabels:
      app: todo
      tier: database
  policyTypes:
  - Ingress
  - Egress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: todo
          tier: backend
    ports:
    - protocol: TCP
      port: 3306

Create the network policy.

$ vim app-stack-network-policy.yaml
$ kubectl create -f app-stack-network-policy.yaml
$ kubectl get networkpolicy --namespace app-stack
NAME                       POD-SELECTOR             AGE
app-stack-network-policy   app=todo,tier=database   5s

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