8-Service

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SERVICE in kubernetes

service is a object in kubernetes that helps in communication between pods and also help in communincation between users or a batabase outside kebernets to talk with pods

types of services - 

NodePort - this makes an internal pod on a node accessable to outside
	nodeport rage - 30000 - 32767
	
	example yml - cat > service-definition.yaml -
	
apiVersion: apps/v1
kind: Service
metadata:
   name:myapp-service(this is name of service)
   labels:
      app: my-app
      costCenter: US
      
spec:
   type: NodePort
   ports:
      - targetPort: 80
        port: 80
        nodeport: 30001
   selector:
      app: my-app
command - kubectl create -f service-definition.yaml
kubectl get services

command to create a nodeport yaml - kubectl expose deployment <name of deployment> --name=<service name> --target-port=<target port> --type=NodePort --port=<port> --dry-run=client -o yaml > service-definition.yaml
ex - kubectl expose deployment simple-webapp-deployment --name=webapp-service --target-port=8080 --type=NodePort --port=8080 --dry-run=client -o yaml > service-definition.yaml
	

ClusterIP - this creates a virual ip inside the cluster that enables the communication b/w different services in the cluster
frnt end service has 3 pods
backend 3pods
key-value store 3 pods
in order to enable comminuincation between them we use clusterIP 

example yml - cat > service-definition.yaml -

apiVersion: apps/v1
kind: Service
metadata:
   name: back-end(this is name of service)
   labels:
      app: my-app
      costCenter: US
      
spec:
   type: ClusterIP
   ports:
      - targetPort: 80
        port: 80
   selector:
      app: my-app
command - kubectl create -f service-definition.yaml
kubectl get services

loadbalancer - node port is useful to expose port to outside but the user need to hits the ip of the pod in order to reach the pod
ex - 
if 3 pods are on ip's 192.168.1.2,3,4
then user can reach the pod using curl http://192.168.1.1 or http://192.168.1.2 or http://192.168.1.2 but the end user need a single ip to hit on to reach the service
Load balancer does this.

This works only in native cloud like aws azure or GCP

example yml - cat > service-definition.yaml -
	
apiVersion: apps/v1
kind: Service
metadata:
   name:myapp-service(this is name of service)
   labels:
      app: my-app
      costCenter: US
      
spec:
   type: LoadBalancer
   ports:
      - targetPort: 80
        port: 80
        nodeport: 30001
   selector:
      app: my-app

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