Exposing Application with a Service

Types of Services:

  • ClusterIP
  • NodePort
  • LoadBalancer
  • ExternalName

kubernetes service

kubectl get pods
kubectl get svc

Sample Output:

NAME                READY     STATUS    RESTARTS   AGE
voting-appp-1j52x   1/1       Running   0          12m
voting-appp-pr2xz   1/1       Running   0          9m
voting-appp-qpxbm   1/1       Running   0          15m

Setting up monitoring

If you are not running a monitoring screen, start it in a new terminal with the following command.

watch -n 1 kubectl get  pod,deploy,rs,svc

Writing Service Spec

Lets start writing the meta information for service.

Filename: vote-svc.yaml

---
apiVersion: v1
kind: Service
metadata:
  name: vote
  labels:
    role: vote
spec:

And then add the spec to it. Refer to Service (v1 core) api at this page https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/

---
apiVersion: v1
kind: Service
metadata:
  name: vote
  labels:
    role: vote
spec:
  selector:
    role: vote
  ports:
    - port: 80
      targetPort: 80
      nodePort: 30000
  type: NodePort

Save the file.

Now to create a service:

kubectl apply -f vote-svc.yaml --dry-run
kubectl apply -f vote-svc.yaml
kubectl get svc

Now to check which port the pod is connected

kubectl describe service vote

Check for the Nodeport here

Sample Output

Name:                     vote
Namespace:                instavote
Labels:                   role=svc
                          tier=front
Annotations:              kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"role":"svc","tier":"front"},"name":"vote","namespace":"instavote"},"spec":{...
Selector:                 app=vote
Type:                     NodePort
IP:                       10.108.108.157
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
NodePort:                 <unset>  31429/TCP
Endpoints:                10.38.0.4:80,10.38.0.5:80,10.38.0.6:80 + 2 more...
Session Affinity:         None
External Traffic Policy:  Cluster
Events:                   <none>

Go to browser and check hostip:NodePort

Here the node port is 31429.

Sample output will be:

Vote

Exposing the app with ExternalIP

spec:
  selector:
    role: vote
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  type: NodePort
  externalIPs:
    - xx.xx.xx.xx
    - yy.yy.yy.yy

Where

replace xx.xx.xx.xx and yy.yy.yy.yy with IP addresses of the nodes on two of the kubernetes hosts.

apply

kubectl  get svc
kubectl apply -f vote-svc.yaml
kubectl  get svc
kubectl describe svc vote

[sample output]

NAME      TYPE       CLUSTER-IP      EXTERNAL-IP                    PORT(S)        AGE
vote      NodePort   10.107.71.204   206.189.150.190,159.65.8.227   80:30000/TCP   11m

where,

EXTERNAL-IP column shows which IPs the application is been exposed on. You could go to http://: to access this application. e.g. http://206.189.150.190:80 where you should replace 206.189.150.190 with the actual IP address of the node that you exposed this on.

Internal Service Discovery

  • Visit the vote app from browser
  • Attemp to vote by clicking on one of the options

observe what happens. Does it go through?

Debugging,

kubectl get pod
kubectl exec vote-xxxx ping redis

[replace xxxx with the actual pod id of one of the vote pods ]

keep the above command on a watch. You should create a new terminal to run the watch command.

e.g.

watch  kubectl exec vote-kvc7j ping redis

where, vote-kvc7j is one of the vote pods that I am running. Replace this with the actual pod id.

Now create redis service

kubectl apply -f redis-svc.yaml

kubectl get svc

kubectl describe svc redis

Watch the ping and observe if its able to resolve redis by hostname and its pointing to an IP address.

e.g.

PING redis (10.102.77.6): 56 data bytes

where 10.102.77.6 is the ClusterIP assigned to the service.

What happened here?

  • Service redis was created with a ClusterIP e.g. 10.102.77.6
  • A DNS entry was created for this service. The fqdn of the service is redis.instavote.svc.cluster.local and it takes the form of my-svc.my-namespace.svc.cluster.local
  • Each pod points to internal DNS server running in the cluster. You could see the details of this by running the following commands
kubectl exec vote-xxxx cat /etc/resolv.conf

[replace vote-xxxx with actual pod id]

[sample output]

nameserver 10.96.0.10
search instavote.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

where 10.96.0.10 is the ClusterIP assigned to the DNS service. You could co relate that with,

kubectl get svc -n kube-system


NAME                   TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)         AGE
kube-dns               ClusterIP   10.96.0.10     <none>        53/UDP,53/TCP   1h
kubernetes-dashboard   NodePort    10.104.42.73   <none>        80:31000/TCP    23m

where, 10.96.0.10 is the ClusterIP assigned to kube-dns and matches the configuration in /etc/resolv.conf above.

Creating Endpoints for Redis

Service is been created, but you still need to launch the actual pods running redis application.

Create the endpoints now,

kubectl apply -f redis-deploy.yaml
kubectl describe svc redis

[sample output]

Name:              redis
Namespace:         instavote
Labels:            role=redis
                   tier=back
Annotations:       kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"role":"redis","tier":"back"},"name":"redis","namespace":"instavote"},"spec"...
Selector:          app=redis
Type:              ClusterIP
IP:                10.102.77.6
Port:              <unset>  6379/TCP
TargetPort:        6379/TCP
Endpoints:         10.32.0.6:6379,10.46.0.6:6379
Session Affinity:  None
Events:            <none>

Again, visit the vote app from browser, attempt to register your vote and observe what happens now.

Reading

Debugging
* Services * Kubernetes Services Documentation * Service API Specs for Kubernetes Version 1.10