Nginx as a Reverse Proxy and Load Balancer

Nginx is a high-performance web server that is widely used as a reverse proxy and load balancer for handling traffic to backend application servers. It efficiently manages request routing, distributes load, and improves fault tolerance.

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1. Basic Reverse Proxy Configuration

A reverse proxy forwards client requests to backend servers, which helps in load balancing, caching, and security.

Example: Proxying Requests to a Backend Server

server {
    listen 80;
    server_name example.com;

    location / {
        proxy_pass http://backend_app;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

upstream backend_app {
    server 127.0.0.1:5000;
}

In this example:

• Requests to example.com are forwarded to the backend application at 127.0.0.1:5000.

• Headers are preserved to ensure correct request information.

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2. Proxying Dynamic Content to Application Servers

Modern applications use various backend technologies. Nginx can proxy requests to Node.js, Python, Java (Spring Boot), PHP, etc.

Example: Proxying Requests to a Node.js Application

server {
    listen 80;
    server_name api.example.com;

    location / {
        proxy_pass http://localhost:3000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
    }
}

Here, requests are forwarded to a Node.js app running on port 3000.

Example: Proxying Requests to a Spring Boot Application

server {
    listen 80;
    server_name spring.example.com;

    location /api/ {
        proxy_pass http://localhost:8080/;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

This proxies API calls to a Spring Boot backend running on 8080.

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3. Load Balancing Algorithms

Nginx supports multiple load balancing strategies to distribute traffic across multiple backend servers.

1. Round Robin (Default)

Requests are evenly distributed among available servers.

upstream backend {
    server app1.example.com;
    server app2.example.com;
}
server {
    location / {
        proxy_pass http://backend;
    }
}

2. Least Connections

Traffic is routed to the server with the fewest active connections.

upstream backend {
    least_conn;
    server app1.example.com;
    server app2.example.com;
}

3. IP Hash (Sticky Sessions)

Requests from the same client IP always go to the same backend server.

upstream backend {
    ip_hash;
    server app1.example.com;
    server app2.example.com;
}

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4. Health Checks & Failover Strategies

Nginx can detect failing servers and redirect traffic accordingly.

Example: Setting Up Health Checks

upstream backend {
    server app1.example.com max_fails=3 fail_timeout=30s;
    server app2.example.com;
}

• If app1.example.com fails 3 times within 30 seconds, it is marked as down.

• Traffic is automatically rerouted to app2.example.com.

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5. Handling WebSockets with Nginx

WebSockets require special handling in Nginx to support persistent connections.

Example: Reverse Proxy WebSockets

server {
    listen 80;
    server_name ws.example.com;

    location /ws/ {
        proxy_pass http://websocket_server;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
    }
}

• WebSockets use the Upgrade header for persistent connections.

• The proxy_http_version 1.1; directive ensures WebSocket compatibility.

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6. Handling CORS with Nginx

CORS (Cross-Origin Resource Sharing) must be configured when serving APIs to prevent security issues.

Example: Allowing CORS for APIs

server {
    listen 80;
    server_name api.example.com;

    location / {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'Content-Type, Authorization';

        if ($request_method = 'OPTIONS') {
            return 204;
        }
    }
}

This configuration allows cross-origin requests and preflight OPTIONS requests for APIs.

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7. Conclusion

Nginx is a powerful tool for proxying requests, balancing traffic, and optimizing application performance. By using the right configurations, you can:

• Distribute load across multiple servers efficiently.

• Ensure high availability with failover strategies.

• Handle WebSockets and CORS seamlessly.