Deploying Web Application on Kubernetes Cluster Using Helm

Step 1: Create a Simple Web Application

We'll use Node.js and Express for the web application. Here's the code for a basic server that takes a name as input and responds with "Happy Learning ".

1.1: Setup the Project

Initialize the Project

 mkdir happy-learning-app
 cd happy-learning-app
 npm init -y

Install Dependencies
```
 npm install express
```

Create the Server Code

Create a file named server.js and add the following code:

 const express = require('express');
 const app = express();
 const port = 3000;

 app.use(express.json());

 app.post('/greet', (req, res) => {
     const name = req.body.name;
     res.send(`Happy Learning ${name}`);
 });

 app.listen(port, () => {
     console.log(`Server running on http://localhost:${port}`);
 });

Create a Dockerfile

Create a Dockerfile in the project root:

 FROM node:14

 # Create app directory
 WORKDIR /usr/src/app

 # Install app dependencies
 COPY package*.json ./
 RUN npm install

 # Bundle app source
 COPY . .

 EXPOSE 3000
 CMD ["node", "server.js"]

Build the Docker Image
```
 docker build -t happy-learning-app .
```

Step 2: Deploy on Kubernetes Using Helm

Setup Helm and Kubernetes Cluster

Ensure you have a Kubernetes cluster running and Helm installed. If you're using a local setup like Minikube, you can start it with:
```
 minikube start
```
Create Helm Chart
```
 helm create happy-learning-chart
```

Modify the Helm Chart

Edit happy-learning-chart/values.yaml to set the image repository and tag:

 image:
   repository: happy-learning-app
   tag: "latest"
   pullPolicy: IfNotPresent

 service:
   type: ClusterIP
   port: 80

 ingress:
   enabled: false

Edit the Deployment Template

Edit happy-learning-chart/templates/deployment.yaml to reflect the port used by our application:

 apiVersion: apps/v1
 kind: Deployment
 metadata:
   name: {{ include "happy-learning-chart.fullname" . }}
   labels:
     {{- include "happy-learning-chart.labels" . | nindent 4 }}
 spec:
   replicas: {{ .Values.replicaCount }}
   selector:
     matchLabels:
       {{- include "happy-learning-chart.selectorLabels" . | nindent 6 }}
   template:
     metadata:
       labels:
         {{- include "happy-learning-chart.selectorLabels" . | nindent 8 }}
     spec:
       containers:
         - name: {{ .Chart.Name }}
           image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
           ports:
             - containerPort: 3000
           livenessProbe:
             httpGet:
               path: /
               port: 3000
           readinessProbe:
             httpGet:
               path: /
               port: 3000
           resources:
             {{- toYaml .Values.resources | nindent 12 }}

Build and Push Docker Image to a Registry

If you are using Docker Hub, tag and push your image:

 docker tag happy-learning-app <your-dockerhub-username>/happy-learning-app:latest
 docker push <your-dockerhub-username>/happy-learning-app:latest

Install the Helm Chart

Update the values.yaml with the appropriate image repository (your Docker Hub username) and then install the chart:
```
 helm install happy-learning happy-learning-chart
```
Access the Application

Find the service IP to access the application:
```
 kubectl get svc
```
Use the cluster IP and the exposed port (default 80 in our values.yaml) to access the application.

Conclusion

You now have a simple web application that takes a name as input and responds with a greeting. This application has been containerized using Docker and deployed to a Kubernetes cluster using Helm. You can access the application by making a POST request to /greet with a JSON payload containing the name field.