CourseDevops

Pet Shelter App - MERN Stack

A simplified 3-tier application built with MongoDB, Express, React (HTML/JS), and Node.js for demonstration purposes.

Project Overview

This is a basic Pet Shelter application that allows users to:

• View all pets in the shelter
• Add new pets to the shelter

The application consists of:

• Frontend: Simple HTML/JavaScript interface served by Express
• Backend: Node.js REST API with two endpoints
• Database: MongoDB for data persistence

Architecture

Frontend (Port 3000) --> Backend API (Port 5100:5000) --> MongoDB (Port 27017)

API Endpoints

• GET /api/pets - Retrieve all pets
• POST /api/pets - Add a new pet

Backend runs on port 5000 inside Docker, mapped to port 5100 on host (Mac uses port 5000 for AirPlay).

Running with Docker Compose

Build and run all services:

docker-compose up --build

Access the application at http://localhost:3000

Building Docker Images for Kubernetes

Build and tag images:

# Backend
cd backend
docker build -t dimilan/pet-shelter-backend:latest .
docker push dimilan/pet-shelter-backend:latest

# Frontend
cd ../frontend
docker build -t dimilan/pet-shelter-frontend:latest .
docker push dimilan/pet-shelter-frontend:latest

Deploying to Kubernetes (Minikube)

1. Start Minikube:

   minikube start
   

2. Build Docker images in Minikube’s Docker daemon: ```bash

   Point shell to minikube’s docker

   eval $(minikube docker-env)

Build backend

cd backend docker build -t dimilan/pet-shelter-backend:latest .

Build frontend

cd ../frontend docker build -t dimilan/pet-shelter-frontend:latest .

cd ..

3. Apply Kubernetes configurations:
```bash
kubectl apply -f k8s/mongodb-secret.yaml
kubectl apply -f k8s/mongodb-configmap.yaml
kubectl apply -f k8s/mongodb-deployment.yaml
kubectl apply -f k8s/backend-deployment.yaml
kubectl apply -f k8s/frontend-deployment.yaml

1. Wait for pods to be ready:

   kubectl get pods -w
   

2. Access the frontend service: ```bash

   Option 1: Use minikube service (creates a tunnel)

   minikube service frontend-service

Option 2: Direct access via NodePort

Get minikube IP

minikube ip

Access at http://:32500

6. Verify the application:
```bash
# Check backend logs for database seeding
kubectl logs -l app=backend

# Should show:
# Connecting to MongoDB...
# Server running on port 5000
# Connected to MongoDB
# Database seeded with initial pets

Note: Images use imagePullPolicy: Never to use locally built images in Minikube instead of pulling from DockerHub.

Kubernetes Resources

• Secret: MongoDB credentials stored as base64 encoded values
  • username: admin (base64: YWRtaW4=)
  • password: password (base64: cGFzc3dvcmQ=)
• ConfigMap: MongoDB connection parameters
  • database-url: mongodb-service
  • database-port: 27017
  • database-name: petshelter
• Deployments: MongoDB, Backend, Frontend
• Services:
  • mongodb-service (ClusterIP on port 27017)
  • backend-service (ClusterIP on port 5000)
  • frontend-service (NodePort on port 32500)

The backend constructs the MongoDB connection string from individual environment variables sourced from the Secret and ConfigMap, following security best practices.

Environment Variables

Backend

• MONGO_URL: MongoDB connection string (from ConfigMap in K8s)
• PORT: Server port (default: 5000)

MongoDB

• MONGO_INITDB_ROOT_USERNAME: Admin username (from Secret in K8s)
• MONGO_INITDB_ROOT_PASSWORD: Admin password (from Secret in K8s)

Notes

• No authentication/authorization implemented
• Minimal error handling
• Designed for learning Docker and Kubernetes concepts
• Uses NodePort service type for easy access in Minikube