🚀 Node.js Express Load Balancer

This project is a simple HTTP Load Balancer built with Node.js and Express. It distributes incoming client requests to multiple backend servers using a round-robin scheduling algorithm. It also performs periodic health checks to ensure only healthy backend servers receive traffic.

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Features

• Round-robin distribution of requests among backend servers
• Periodic health checks to monitor backend server availability
• Automatic removal and re-addition of backends based on health status
• Handles multiple concurrent client requests
• Easy to test with Python's built-in HTTP server

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Requirements

• Node.js (v14 or later)
• Python 3 (optional, for running test backend servers)

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Setup and Usage

1. Clone this repository

git clone https://github.com/Harsh72019/loadBalancer.git
cd loadBalancer

2. Install dependencies

npm install

3. Run backend servers (for testing)

Use Python's built-in HTTP server to quickly start backend servers:

mkdir server8080 && echo "Hello from 8080" > server8080/index.html
mkdir server8081 && echo "Hello from 8081" > server8081/index.html
mkdir server8082 && echo "Hello from 8082" > server8082/index.html

# Open three terminals and run:
python3 -m http.server 8080 --directory server8080
python3 -m http.server 8081 --directory server8081
python3 -m http.server 8082 --directory server8082

4. Start the load balancer

node loadBalancer.js

The load balancer listens on port 3000 by default.

5. Test the load balancer

Use curl or a browser to send requests to the load balancer:

curl http://localhost:3000

You should see responses rotating between the backend servers (8080, 8081, 8082).

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Health Checks

The load balancer performs a health check every 10 seconds (configurable in loadBalancer.js) by sending a GET request to each backend’s root path (/). Only servers responding with HTTP 200 are considered healthy.

If a backend fails the health check, it is temporarily removed from rotation. When it passes again, it is added back automatically.

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Testing Concurrent Requests

Create a file urls.txt with repeated URLs:

url = "http://localhost:3000"
url = "http://localhost:3000"
url = "http://localhost:3000"
url = "http://localhost:3000"

Run parallel curl requests:

curl --parallel --parallel-max 3 --config urls.txt

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Customization

• Change backend servers by editing the backends array in loadBalancer.js
• Adjust health check interval by modifying HEALTH_CHECK_INTERVAL
• Modify health check path by changing HEALTH_CHECK_PATH

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License

MIT License

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Author

Harsh Bali — harshbali374@gmail.com

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Feel free to open issues or submit pull requests for improvements!