Kubernetes-Services

 

Kubernetes-Services

An abstract way to expose an application running on a set of Pods as a network service.

With Kubernetes you don't need to modify your application to use an unfamiliar service discovery mechanism. Kubernetes gives Pods their own IP addresses and a single DNS name for a set of Pods, and can load-balance across them

CLUSTER IP

ClusterIP is the default kubernetes service. This service is created inside a cluster and can only be accessed by other pods in that cluster. So basically we use this type of service when we want to expose a service to other pods within the same cluster.

Nodeport:

NodePort opens a specific port on your node/VM and when that port gets traffic, that traffic is forwarded directly to the service.

There are a few limitations and hence its not advised to use NodePort

- only one service per port

- You can only use ports 30000-32767

LoadBalancer:

This is the standard way to expose service to the internet. All the traffic on the port is forwarded to the service. It's designed to assign an external IP to act as a load balancer for the service.  There's no filtering, no routing. LoadBalancer uses cloud service

Few limitations with LoadBalancer:

- every service exposed will it's own ip address 

- It gets very expensive 

Lab for Cluster IP service

1. Create a deployment

2. Access the application which is deployed internally using ClusterIP

Deployment YAML file:

# Deployment

# nginx-deploy.yaml

apiVersion: apps/v1

kind: Deployment

metadata:

  name: nginx-deployment

  labels:

    app: nginx-app

spec:

  replicas: 3

  selector:

    matchLabels:

      app: nginx-app

  template:

    metadata:

      labels:

        app: nginx-app

    spec:

      containers:

      - name: nginx-container

        image: nginx

        ports:

        - containerPort: 80

kubectl create -f nginx-deploy.yaml

Kubectl get pods -o wide

Create a ClusterIP service

# Service- ClusterIP

# nginx-svc-ci.yaml

apiVersion: v1

kind: Service

metadata:

  name: internal-service

  labels:

    app: nginx-app

spec:

  selector:

    app: nginx-app

  type: ClusterIP

  ports:

  - port: 80

    targetPort: 80

kubectl create -f nginx-svc-ci.yml

 Run below command and You can see the internal-service in the list with a static IP address.

kubectl get svc  

To see all the End Points (IP addresses of the Pods which are associated with service)

kubectl describe svc internal-service

Remove one of the pod and monitor the Endpoints

To access the application you need to use the IP address of service with port number.

Delete the CI service

 kubectl delete svc internal-service

NodePort Service

Create Node Port service

# Service- NodePort

# nginx-svc-np.yaml

apiVersion: v1

kind: Service

metadata:

  name: external-service

  labels:

    app: nginx-app

spec:

  selector:

    app: nginx-app

  type: NodePort

  ports:

  - nodePort: 31869

    port: 80

    targetPort: 80

Create NodePort service

kubectl create -f nginx-svc-np.yml

kubectl get svc

kubectl describe svc  external-service

Remove one of the pod and monitor the Endpoints

To access the application you need to use the IP address of service with port number.

You can access the application on browser by providing the IP address of you any node with port number 31869 ...IP:31869

kubectl delete svc external-service

LoadBalancer service

# Service- LoadBalancer

# nginx-svc-lb.yaml

apiVersion: v1

kind: Service

metadata:

  name: external-service

  labels:

    app: nginx-app

spec:

  selector:

    app: nginx-app

  type: LoadBalancer

  ports:

  - nodePort: 31869

    port: 80

    targetPort: 80

Create LoadBalancer service

kubectl create -f nginx-svc-lb.yml

kubectl get svc

The External IP is to be provided by the load balancer ( more suitable in cloud based environment) if there is not load balancer then the external ip is in the pending state.

kubectl describe svc  external-service

Remove one of the pod and monitor the Endpoints

To access the application you need to use the IP address of service with port number.

You can access the application on browser by providing the IP address of you any node with port number 31869 ...IP:31869

kubectl delete svc external-service

Delete the Deploy

kubectl delete deploy nginx-deployment

Ingress

Ingress exposes HTTP and HTTPS routes from outside the cluster to services within the cluster. Traffic routing is controlled by rules defined on the Ingress resource.

    internet
        |
   [ Ingress ]
   --|-----|--
   [ Services ]

An Ingress may be configured to give Services externally-reachable URLs, load balance traffic, terminate SSL / TLS, and offer name-based virtual hosting. An Ingress controller is responsible for fulfilling the Ingress, usually with a load balancer, though it may also configure your edge router or additional frontends to help handle the traffic.

Install nginx ingress Controller

kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v0.35.0/deploy/static/provider/baremetal/deploy.yaml

A new namespace ingress-nginx will be created.

kubectl get ns

Find the services under ingress-nginx namespace

kubectl get svc -n ingress-nginx

Create a pod with image nginx

kubectl run nginx --image=nginx

Create a Cluster IP service nginx which targets nginx pod.

kubectl expose pod nginx --type=ClusterIP --port=80

Create a pod with image tomcat

kubectl run tomcat --image=tomcat

Create another Cluster  IP service which points to tomcat pod

kubectl expose pod tomcat --type=ClusterIP --port=8080

Create a ingress to access the cluster ip services externally.

#ingress.yaml

apiVersion: extensions/v1beta1

kind: Ingress

metadata:

  name: simple-fanout-example

  annotations:

   nginx.ingress.kubernetes.io/rewrite-target: /

spec:

  rules:

  - http:

     paths:

     - path: /nginx

       backend:

        serviceName: nginx

        servicePort: 80

     - path: /web

       backend:

        serviceName: tomcat

        servicePort: 8080  

kubectl create -f ingress.yaml

kubectl get ingress

Find the http port number for the ingress controller's NodePort service.

kubectl get svc -n ingress-nginx