# Nginx Quick Reference

*Server blocks, proxying, SSL, load balancing, logging*

> Source: Nginx Documentation (nginx.org/en/docs) · MIT

## Installation

### Install by OS

| Command | Description |
|---------|-------------|
| `Ubuntu / Debian` | `sudo apt install nginx` |
| `RHEL / CentOS` | `sudo dnf install nginx` |
| `macOS` | `brew install nginx` |
| `Alpine` | `apk add nginx` |
| `Docker` | `docker run -p 80:80 nginx` |

### Service Management

| Command | Description |
|---------|-------------|
| `sudo systemctl start nginx` | Start Nginx |
| `sudo systemctl stop nginx` | Stop Nginx |
| `sudo systemctl reload nginx` | Reload config (no downtime) |
| `sudo systemctl enable nginx` | Enable on boot |
| `nginx -t` | Test config syntax |
| `nginx -T` | Test and dump full config |
| `nginx -s reload` | Signal running process to reload |

## Basic Config

### File Locations

| Command | Description |
|---------|-------------|
| `/etc/nginx/nginx.conf` | Main configuration file |
| `/etc/nginx/conf.d/` | Drop-in site configs (*.conf) |
| `/etc/nginx/sites-available/` | Available site configs (Debian) |
| `/etc/nginx/sites-enabled/` | Symlinks to active configs |
| `/var/log/nginx/` | Access and error logs |
| `/var/www/html/` | Default document root |

### Minimal Config

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

### Config Structure

| Command | Description |
|---------|-------------|
| `http { }` | HTTP server settings (top level) |
| `server { }` | Virtual host definition |
| `location { }` | URI matching block |
| `upstream { }` | Backend server group |
| `events { }` | Connection handling settings |

## Server Blocks

### Name-Based Virtual Hosts

```
server {
    listen 80;
    server_name site-a.com;
    root /var/www/site-a;
}
server {
    listen 80;
    server_name site-b.com;
    root /var/www/site-b;
}
```

### Default & Catch-All

```
server {
    listen 80 default_server;
    server_name _;
    return 444;  # drop connection
}
```

### HTTPS Redirect

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

## Location Blocks

### Match Priority (high to low)

| Command | Description |
|---------|-------------|
| `= /path` | Exact match (highest priority) |
| `^~ /path` | Prefix match, skip regex |
| `~ regex` | Case-sensitive regex |
| `~* regex` | Case-insensitive regex |
| `/path` | Prefix match (lowest priority) |

### Location Examples

```
location = / {
    # exact root only
}
location /api/ {
    proxy_pass http://backend;
}
location ~* \.(jpg|png|gif)$ {
    expires 30d;
}
```

### try_files

```
location / {
    try_files $uri $uri/ /index.html;
}
```

*Try file, then directory, then fallback -- essential for SPAs*

## Reverse Proxy

### Basic Proxy

```
location /api/ {
    proxy_pass http://localhost:3000/;
    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;
}
```

### WebSocket Proxy

```
location /ws/ {
    proxy_pass http://localhost:3000;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
}
```

### Proxy Directives

| Command | Description |
|---------|-------------|
| `proxy_pass` | Backend URL |
| `proxy_set_header` | Pass custom headers to backend |
| `proxy_read_timeout` | Timeout for backend response (default 60s) |
| `proxy_buffering off` | Disable response buffering |
| `proxy_redirect` | Rewrite Location headers from backend |

## SSL / TLS

### HTTPS Server

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

    ssl_certificate     /etc/ssl/certs/example.crt;
    ssl_certificate_key /etc/ssl/private/example.key;
    ssl_protocols       TLSv1.2 TLSv1.3;
    ssl_ciphers         HIGH:!aNULL:!MD5;
}
```

### Let's Encrypt with Certbot

```
sudo certbot --nginx -d example.com
sudo certbot renew --dry-run
```

### SSL Best Practices

| Command | Description |
|---------|-------------|
| `ssl_protocols TLSv1.2 TLSv1.3` | Disable old TLS versions |
| `ssl_prefer_server_ciphers on` | Server chooses cipher |
| `ssl_session_cache shared:SSL:10m` | Session reuse for performance |
| `add_header Strict-Transport-Security` | HSTS header |
| `ssl_stapling on` | OCSP stapling for faster handshake |

## Load Balancing

### Upstream Block

```
upstream backend {
    server 10.0.0.1:3000;
    server 10.0.0.2:3000;
    server 10.0.0.3:3000;
}
server {
    location / {
        proxy_pass http://backend;
    }
}
```

### Load Balancing Methods

| Command | Description |
|---------|-------------|
| `(default)` | Round-robin |
| `least_conn` | Fewest active connections |
| `ip_hash` | Client IP sticky sessions |
| `hash $request_uri` | Consistent hash by URI |

### Server Options

| Command | Description |
|---------|-------------|
| `weight=3` | Send 3x more traffic |
| `max_fails=3` | Failures before marking down |
| `fail_timeout=30s` | Time to mark server as down |
| `backup` | Use only when others are down |
| `down` | Mark server as permanently offline |

## Static Files & Caching

### Serve Static Files

```
location /static/ {
    alias /var/www/assets/;
    expires 30d;
    add_header Cache-Control "public, immutable";
}
```

### Gzip Compression

```
gzip on;
gzip_types text/plain text/css
           application/json application/javascript;
gzip_min_length 1000;
gzip_comp_level 5;
```

### Caching Directives

| Command | Description |
|---------|-------------|
| `expires 30d` | Set Expires and Cache-Control max-age |
| `expires off` | Disable expires header |
| `etag on` | Enable ETag header (default) |
| `sendfile on` | Efficient file serving via kernel |
| `tcp_nopush on` | Optimize packet sending |

## Logging

### Log Configuration

```
access_log /var/log/nginx/access.log;
error_log  /var/log/nginx/error.log warn;

# Custom log format
log_format main '$remote_addr - $status '
                '"$request" $body_bytes_sent';
access_log /var/log/nginx/access.log main;
```

### Error Log Levels

| Command | Description |
|---------|-------------|
| `debug` | Verbose (requires --with-debug) |
| `info` | Informational |
| `notice` | Normal but notable |
| `warn` | Warnings |
| `error` | Errors (default) |
| `crit` | Critical issues |

### Conditional Logging

```
map $status $loggable {
    ~^[23] 0;
    default 1;
}
access_log /var/log/nginx/access.log combined if=$loggable;
```

*Skip logging 2xx/3xx responses to reduce log volume*

## Security

### Rate Limiting

```
limit_req_zone $binary_remote_addr
    zone=api:10m rate=10r/s;

location /api/ {
    limit_req zone=api burst=20 nodelay;
}
```

### Access Control

```
location /admin/ {
    allow 192.168.1.0/24;
    deny all;
}
```

### Security Headers

| Command | Description |
|---------|-------------|
| `X-Frame-Options DENY` | Prevent clickjacking |
| `X-Content-Type-Options nosniff` | Prevent MIME sniffing |
| `X-XSS-Protection "1; mode=block"` | XSS filter (legacy browsers) |
| `Content-Security-Policy` | Control resource loading sources |
| `Referrer-Policy no-referrer` | Control referrer information |

## Common Patterns

### SPA (Single-Page App)

```
location / {
    root /var/www/app;
    try_files $uri $uri/ /index.html;
}
```

### CORS Headers

```
location /api/ {
    add_header Access-Control-Allow-Origin *;
    add_header Access-Control-Allow-Methods
               "GET, POST, PUT, DELETE, OPTIONS";
    if ($request_method = OPTIONS) {
        return 204;
    }
    proxy_pass http://backend;
}
```

### Useful Variables

| Command | Description |
|---------|-------------|
| `$host` | Request Host header |
| `$uri` | Current URI (normalized) |
| `$request_uri` | Original URI with query string |
| `$remote_addr` | Client IP address |
| `$scheme` | http or https |
| `$args` | Query string parameters |
| `$status` | Response status code |