configuring-nginx

# Configuring nginx

## Purpose

Guide engineers through configuring nginx for common web infrastructure needs: static file serving, reverse proxying backend applications, load balancing across multiple servers, SSL/TLS termination, caching, and performance optimization. Provides production-ready configurations with security best practices.

## When to Use This Skill

Use when working with:
- Setting up web server for static sites or single-page applications
- Configuring reverse proxy for Node.js, Python, Ruby, or Go applications
- Implementing load balancing across multiple backend servers
- Terminating SSL/TLS for HTTPS traffic
- Adding caching layer for performance improvement
- Building API gateway functionality
- Protecting against DDoS with rate limiting
- Proxying WebSocket connections

Trigger phrases: "configure nginx", "nginx reverse proxy", "nginx load balancer", "enable SSL in nginx", "nginx performance tuning", "nginx caching", "nginx rate limiting"

## Installation

**Ubuntu/Debian:**
```bash
sudo apt update && sudo apt install nginx -y
sudo systemctl enable nginx
sudo systemctl start nginx
```

**RHEL/CentOS/Rocky:**
```bash
sudo dnf install nginx -y
sudo systemctl enable nginx
sudo systemctl start nginx
```

**Docker:**
```bash
docker run -d -p 80:80 -v /path/to/config:/etc/nginx/conf.d nginx:alpine
```

## Quick Start Examples

### Static Website

Serve HTML/CSS/JS files from a directory:

```nginx
server {
    listen 80;
    server_name example.com www.example.com;
    root /var/www/example.com/html;
    index index.html;

    location / {
        try_files $uri $uri/ =404;
    }

    location ~* \.(jpg|jpeg|png|gif|ico|css|js|woff2)$ {
        expires 1y;
        add_header Cache-Control "public, immutable";
    }
}
```

Enable site:
```bash
sudo ln -s /etc/nginx/sites-available/example.com /etc/nginx/sites-enabled/
sudo nginx -t && sudo systemctl reload nginx
```

See `references/static-sites.md` for SPA configurations and advanced patterns.

### Reverse Proxy

Proxy requests to a backend application server:

```nginx
upstream app_backend {
    server 127.0.0.1:3000;
    keepalive 32;
}

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

    location / {
        proxy_pass http://app_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;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
    }
}
```

See `references/reverse-proxy.md` for WebSocket proxying and API gateway patterns.

### SSL/TLS Configuration

Enable HTTPS with modern TLS configuration:

```nginx
server {
    listen 443 ssl http2;
    server_name example.com;

    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    ssl_protocols TLSv1.3 TLSv1.2;
    ssl_prefer_server_ciphers off;
    ssl_session_cache shared:SSL:50m;
    ssl_session_timeout 1d;

    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;

    location / {
        try_files $uri $uri/ =404;
    }
}

server {
    listen 80;
    server_name example.com;
    return 301 https://$server_name$request_uri;
}
```

See `references/ssl-tls-config.md` for complete TLS configuration and certificate setup.

## Core Concepts

### Configuration Structure

nginx uses hierarchical configuration contexts:

```
nginx.conf (global settings)
├── events { } (connection processing)
└── http { } (HTTP-level settings)
    └── server { } (virtual host)
        └── location { } (URL routing)
```

**File locations:**
- `/etc/nginx/nginx.conf` - Main configuration
- `/etc/nginx/sites-available/` - Available site configs
- `/etc/nginx/sites-enabled/` - Enabled sites (symlinks)
- `/etc/nginx/conf.d/*.conf` - Additional configs
- `/etc/nginx/snippets/` - Reusable config snippets

See `references/configuration-structure.md` for detailed anatomy.

### Location Matching Priority

nginx evaluates location blocks in this order:

1. `location = /exact` - Exact match (highest priority)
2. `location ^~ /prefix` - Prefix match, stop searching
3. `location ~ \.php$` - Regex, case-sensitive
4. `location ~* \.(jpg|png)$` - Regex, case-insensitive
5. `location /` - Prefix match (lowest priority)

Example:
```nginx
location = /api/status {
    return 200 "OK\n";
}

location ^~ /static/ {
    root /var/www;
}

location ~ \.php$ {
    fastcgi_pass unix:/var/run/php/php-fpm.sock;
}

location / {
    proxy_pass http://backend;
}
```

### Essential Proxy Headers

When proxying to backends, preserve client information:

```nginx
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;
```

Create reusable snippet at `/etc/nginx/snippets/proxy-params.conf` and include with:
```nginx
include snippets/proxy-params.conf;
```

## Common Patterns

### Load Balancing

Distribute traffic across multiple backend servers:

**Round Robin (default):**
```nginx
upstream backend {
    server backend1.example.com:8080;
    server backend2.example.com:8080;
    server backend3.example.com:8080;
    keepalive 32;
}

server {
    listen 80;
    location / {
        proxy_pass http://backend;
        include snippets/proxy-params.conf;
    }
}
```

**Least Connections:**
```nginx
upstream backend {
    least_conn;
    server backend1.example.com:8080;
    server backend2.example.com:8080;
}
```

**IP Hash (sticky sessions):**
```nginx
upstream backend {
    ip_hash;
    server backend1.example.com:8080;
    server backend2.example.com:8080;
}
```

**Health Checks:**
```nginx
upstream backend {
    server backend1.example.com:8080 max_fails=3 fail_timeout=30s;
    server backend2.example.com:8080 max_fails=3 fail_timeout=30s;
    server backup.example.com:8080 backup;
}
```

See `r