Real-Time Polling System

A scalable real-time polling system built with Node.js, Express, PostgreSQL, Kafka, and WebSocket. This system allows users to create polls, cast votes, and get real-time updates on voting results.

Features

• Create and manage polls with multiple options
• Real-time vote tracking using WebSocket
• Event-driven architecture using Kafka
• RESTful API endpoints
• Leaderboard system with time-based filtering
• Comprehensive statistics and analytics
• Database persistence with PostgreSQL
• Scalable and maintainable codebase

Prerequisites

• Node.js (v14 or higher)
• PostgreSQL (v12 or higher)
• Apache Kafka
• npm or yarn

Installation

1. Clone the repository:

git clone [repository-url]
cd polling-system

2. Install dependencies:

npm install

3. Set up environment variables:

Create a .env file in the root directory and add the following configurations:

PORT=3000
DB_HOST=localhost
DB_PORT=5432
DB_USER=postgres
DB_PASSWORD=your_password
DB_NAME=polling_system

4. Set up PostgreSQL database:

CREATE DATABASE polling_system;

5. Start Kafka server and create required topics:

Start Zookeeper

To start the Zookeeper server, run the following command:

bin/zookeeper-server-start.sh config/zookeeper.properties

Start Kafka

To start the Kafka, run the following command:

bin/kafka-server-start.sh config/server.properties

Create topic

bin/kafka-topics.sh --create --topic poll-votes --bootstrap-server localhost:9092 --partitions 1 --replication-factor 1

Project Structure

src/
├── config/
│   ├── database.js
│   └── kafka.js
├── controllers/
│   ├── pollController.js
│   ├── voteController.js
│   └── leaderboardController.js
├── models/
│   ├── index.js
│   ├── Poll.js
│   ├── Option.js
│   └── Vote.js
├── routes/
│   ├── pollRoutes.js
│   ├── voteRoutes.js
│   └── leaderboardRoutes.js
├── services/
│   ├── pollService.js
│   ├── voteService.js
│   ├── kafkaService.js
│   ├── websocketService.js
│   └── leaderboardService.js
└── server.js

API Endpoints

Polls

POST /api/v1/polls/createPoll

• Create a new poll

GET /api/v1/polls/getPoll/:id

• Get poll by ID

GET /api/v1/polls/allpolls

• List all polls

Votes

POST /api/v1/vote/:optionId

• Cast a vote for an option

Leaderboard

GET /api/v1/leaderboard/:pollId?

• Get a leaderboard for a specific poll

GET /api/v1/leaderboard/:pollId/option/:optionId

• Get the leaderboard for a specific option within a poll

WebSocket Events

Client -> Server

// Cast a vote
{
    type: 'vote',
    data: {
        userId: 'string',
        optionId: 'string'
    }
}

Server -> Client

// Vote update
{
    type: 'vote_update',
    data: {
        optionId: 'string',
        newVoteCount: number
    }
}

Running the Application

Start the server:

npm start

Test WebSocket connection (optional):

node src/testWebSocketClient.js

Testing

To run the test WebSocket client:

node src/testWebSocketClient.js

Error Handling

The application includes comprehensive error handling:

• Input validation

• Database connection errors

• WebSocket connection errors

• Kafka producer/consumer errors

• Duplicate vote prevention

Contributing

• Fork the repository

• Create your feature branch (git checkout -b feature/AmazingFeature)

• Commit your changes (git commit -m 'Add some AmazingFeature')

• Push to the branch (git push origin feature/AmazingFeature)

• Open a Pull Request

License

This project is licensed under the MIT License.