Spring Boot + Kubernetes Tutorial - Difference between ClusterIP, NodePort and LoadBalancer Service

In previous tutorial we deployed spring boot application to kubernetes pod. In this tutorial we will be looking at what are services. Using services we will be able to access the application deployed on pods. In Kubernetes, services are a fundamental concept that allows applications to communicate with each other within the cluster. Think of services as an abstraction layer that acts as a single entry point, providing a stable and reliable way for different components of your application to find and interact with each other.

Spring Boot + Kubernetes Tutorial
What is Kubernetes? Need for it?
Install Ubuntu on Windows using WSL 
Installing Kubectl, Minikube and Docker on Ubuntu
Create Docker Image
Deploy to Minikube Pods
Difference between ClusterIP, NodePort and LoadBalancer Service
Service Hello World Example

Services Overview

In the kubernetes documentation they have given sample service file. We will be making use of this sample file as a reference. There are 3 types of services-

1. ClusterIP - In Kubernetes, Clusterip services help applications within the cluster communicate with each other.
   For example we have microservice-consumer consuming the REST endpoint exposed by microservice-producer programatically.
   
   
   In such a scenario when we deploy these applications as kubernetes pods,we do not want the employee-producer pod exposed outside the cluster, but just internally for employee-consumer pod. So we will define a service of type clusterip for employee-producer.
   
   
   
   In the below diagram I have a scenario where we have 3 replicas of the employee-producer and single instance of employee-consumer. When the employee-consumer calls the service, the request can be forwarded to any of the employee-producer pod by the clusterip service.
   
   

   apiVersion: v1
   kind: Service
   metadata:
     name: employee-producer-service
   spec:
     selector:
       app: boot-jar
     ports:
       - protocol: TCP
         port: 80
         targetPort: 8080
     type: ClusterIP
   

   Clusterip provides loadbalancing at the pod level and not the node level.
2. NodePort - NodePort services in Kubernetes are a way to expose your application to the outside world or make it accessible from outside the cluster.
   Again consider the employee-producer service which has exposed some rest endpoints. This is deployed as a kubernetes pod. The exposed REST endpoints are now to be consumed not by an internal client within the kubernetes but external client outside the cluster. So in this scenario for the employee producer pod we define a service of type nodeport.
   
   
   With NodePort services, a specific port on every node in the cluster is allocated to your application. This port should be above 30000.
   
   

   apiVersion: v1
   kind: Service
   metadata:
     name: employee-producer-service
   spec:
     selector:
       app: boot-jar
     ports:
       - protocol: TCP
         port: 80
         targetPort: 8080
         nodePort: 30080
     type: NodePort
   

   Within the cluster nodeport works similar to the way clusterip works. If any external client wants to access the application running on pod then it will need to make a call to the node directly on the nodeport. The main disadvantage of using nodeport is exposing the nodes directly to the external client. Also the unusual port numbers may cause firewall issues. So this type of service is mostly used for development purpose.
3. LoadBalancer - LoadBalancer services provide a public IP address and port that act as an entry point for external traffic.
   Again consider the employee-producer service which has exposed some rest endpoints. This is deployed as a kubernetes pod. The exposed REST endpoints are to be consumed not by an internal client within the kubernetes but external client outside the cluster. So in this scenario for the employee producer pod we define a service of type loadbalancer.
   
   
   Unlike the nodeport service there are no port restrictions for loadbalancer service.
   
   

   apiVersion: v1
   kind: Service
   metadata:
     name: employee-producer-service
   spec:
     selector:
       app: boot-jar
     ports:
       - protocol: TCP
         port: 80
         targetPort: 8080
     type: LoadBalancer
   

   Loadbalancer works similar to nodeport in exposing the deployed pod applications to external clients. So if nodeport already exposes the pod application to the external client then what is the need for loadbalancer. Loadbalancer creates an abstraction layer for the external client which redirect their requests to the appropriate node. With loadbalancer the client is not aware of the internal node structure and also if the request is being forwarded to which of the available nodes. As the name suggests loadbalancer balances the load between different nodes by distributing the requests between the nodes. Cloud platforms like Azure, AWS, GCP provide out of the box loadbalancer which can be used. The major downside of using loadbalancer is the additional cloud billing cost associated with using them.