This project demonstrates how to set up an Nginx server as both a reverse proxy and load balancer. It distributes incoming HTTP requests between two backend servers (with hidden IP addresses) and provides a monitoring endpoint and custom logging to track which backend server handled each request.

Table of Contents

• Overview
• Prerequisites
• Project Structure
• Nginx Basics
• Configuration Details
  • Global Configuration (nginx.conf)
  • Site Configuration (default in sites-enabled)
• Commands & Testing
• Monitoring & Logs
• Summary

Overview

This setup allows a local Ubuntu server to act as a gateway for incoming requests by:

• Reverse Proxying: Accepting client requests and forwarding them to backend servers.
• Load Balancing: Distributing requests between multiple backend servers using a round-robin mechanism.
• Monitoring: Using the stub_status module to monitor active connections and performance metrics.
• Custom Logging: Recording which backend server (using hidden IP addresses) handled each request via a custom log format.

Prerequisites

• Ubuntu server with Nginx installed.
• Two backend servers running a web server (Nginx, Apache, etc.) serving your HTML page.
• Basic knowledge of Linux command-line operations.

Project Structure

The key Nginx configuration files used are:

/etc/nginx/
├── nginx.conf            # Global configuration
├── sites-available/
│   └── default           # Site-specific configuration for reverse proxy/load balancing
└── sites-enabled/
    └── default           # Symlink to sites-available/default

Nginx Basics

Nginx is a powerful web server used for:

• Serving static and dynamic content.
• Acting as a reverse proxy to hide backend server details.
• Load balancing incoming requests to multiple servers.
• Monitoring performance via modules like stub_status.

Key Directives

• upstream: Groups backend servers for load balancing.
• server: Defines a virtual host.
• location: Specifies how to handle requests for specific URIs.
• proxy_pass: Forwards requests to the backend.
• stub_status: Provides basic server status information for monitoring.

Configuration Details

Install Nginx

If Nginx is not already installed, you can install it using:

sudo apt update
sudo apt install nginx

Global Configuration (nginx.conf)

This file sets up general server settings, including a custom log format that logs which backend handled each request.

sudo nano /etc/nginx/nginx.conf

user www-data;
worker_processes auto;
pid /run/nginx.pid;
error_log /var/log/nginx/error.log;
include /etc/nginx/modules-enabled/*.conf;

events {
    worker_connections 768;
}

http {
    # Basic Settings
    sendfile on;
    tcp_nopush on;
    types_hash_max_size 2048;
    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    # SSL Settings (adjust as needed)
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3;
    ssl_prefer_server_ciphers on;

    # Custom Logging Settings
    log_format upstreamlog '$remote_addr - $remote_user [$time_local] '
                           '"$request" $status $body_bytes_sent '
                           '"$http_referer" "$http_user_agent" '
                           'upstream: "$upstream_addr" '
                           'request_time: $request_time '
                           'upstream_response_time: $upstream_response_time';
    access_log /var/log/nginx/access.log upstreamlog;

    # Gzip Compression
    gzip on;

    # Include Additional Configuration Files
    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

Site Configuration (/etc/nginx/sites-enabled/default)

This file defines the reverse proxy and load balancing configuration along with a monitoring endpoint. The backend IP addresses are hidden (represented as placeholders).

sudo nano /etc/nginx/sites-enabled/default

# Define the backend servers (hidden IPs)
upstream backend {
    server 192.0.2.1;  # Backend Server 1 (hidden IP)
    server 192.0.2.2;  # Backend Server 2 (hidden IP)
}

server {
    listen 80 default_server;
    listen [::]:80 default_server;
    server_name _;

    # Monitoring endpoint using stub_status
    location /nginx_status {
        stub_status;
        allow 127.0.0.1;  # Restrict access to local machine; adjust as needed
        deny all;
    }

    # Reverse Proxy and Load Balancing
    location / {
        proxy_pass http://backend;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Commands & Testing

1. Test Nginx Configuration

Before reloading Nginx, check for syntax errors:

sudo nginx -t

2. Reload Nginx

If the configuration test passes, reload Nginx to apply the changes:

sudo systemctl reload nginx

3. Generate a New Request

To ensure your requests are not cached (which may skip the proxy logic), use:

curl -H "Cache-Control: no-cache" http://<YOUR_LOCAL_SERVER_IP>/

Monitoring & Logs

View Nginx Status

Access the monitoring endpoint from the local machine:

curl http://127.0.0.1/nginx_status

This will display active connections and other metrics provided by Nginx.

Check the Logs

To monitor which backend server handled each request, tail the access log:

sudo tail -f /var/log/nginx/access.log

In the log entries, look for the upstream: "..." field which shows the backend IP (e.g., "192.0.2.1" or "192.0.2.2").

Summary

• Reverse Proxy & Load Balancing:
  Incoming requests to your local server are forwarded to one of the backend servers (hidden IPs) using the upstream block. Load balancing is done using a round-robin mechanism.

• Monitoring:
  The /nginx_status endpoint provides real-time metrics about Nginx performance.

• Custom Logging:
  The custom log format in nginx.conf includes the $upstream_addr variable so you can see which backend server processed each request.

• Testing & Deployment:
  Use the provided commands (nginx -t, systemctl reload nginx, curl, and tail) to test and monitor your configuration.