Nginx from Basics to Advanced

Part 1: Basics

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1. What is Nginx?

Nginx (pronounced "engine-x") is a powerful, high-performance open-source web server developed by Igor Sysoev in 2004. Originally created to solve the C10K problem (handling 10,000 concurrent connections), Nginx has quickly become one of the most popular web servers in the world.

Nginx is not just a web server — it can also function as:

• Reverse proxy server
• Load balancer
• HTTP cache
• Mail proxy server
• API Gateway

Event-driven and Non-blocking I/O Architecture

Nginx's greatest strength lies in its architecture. Unlike the traditional model, Nginx uses an event-driven and non-blocking I/O (asynchronous) architecture.

How it works:

1. Master Process: A single master process reads and evaluates the configuration, and manages worker processes
2. Worker Processes: Multiple worker processes handle the actual connections
3. Event Loop: Each worker process uses an event loop to handle thousands of connections simultaneously

Non-blocking I/O means:

• When a worker process is waiting for I/O (file reads, database queries, network requests), it is not "blocked" — it can handle other requests in the meantime
• A single worker process can handle thousands of connections simultaneously
• Significant savings in CPU and RAM resources

Illustrative example:

Apache (Blocking):
Request 1 → Thread 1 → Wait for file read (blocked) → Complete
Request 2 → Thread 2 → Wait for file read (blocked) → Complete
Request 3 → Thread 3 → Wait for file read (blocked) → Complete
→ 3 threads needed for 3 requests
Nginx (Non-blocking):
Request 1 → Worker → Wait for I/O → Handle Request 2 → Handle Request 3 → Request 1 done
Request 2 → Same Worker
Request 3 → Same Worker
→ Only 1 worker needed for 3 requests

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2. Nginx vs Apache Comparison

Criterion	Nginx	Apache
Architecture	Event-driven, asynchronous	Process/Thread-based
Connection handling	One worker handles many connections	One thread/process per connection
Memory	Very low, stable	Grows with connection count
Static content	Extremely fast	Fast but slower than Nginx
Dynamic content	Requires backend integration (PHP-FPM)	Can handle directly (mod_php)
Configuration	Centralized, file-based	Distributed (.htaccess)
Modules	Must be compiled in advance	Dynamic module loading
Rewrite rules	Different, simpler	Powerful via .htaccess
Best suited for	High traffic, static content, reverse proxy	Shared hosting, dynamic content processing

When to use Nginx:

• Serving static files (HTML, CSS, JS, images)
• Reverse proxy for application servers
• Load balancing
• High concurrency (many simultaneous connections)
• High performance with limited resources

When to use Apache:

• Shared hosting environments
• Need .htaccess flexibility
• Many dynamic modules
• Legacy applications dependent on Apache-specific features

Current trend: Many systems use a combination: Nginx as the front-facing reverse proxy, Apache handling dynamic content behind it.

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3. Installing Nginx

3.1. Install on Ubuntu/Debian

Method 1: Install from default repository (simplest)

# Update package list
sudo apt update
Install Nginx
sudo apt install nginx -y
Check version
nginx -v
Check status
sudo systemctl status nginx

Method 2: Install from official Nginx repository (latest version)

# Install prerequisites
sudo apt install curl gnupg2 ca-certificates lsb-release ubuntu-keyring

Import official nginx signing key
curl https://nginx.org/keys/nginx_signing.key | gpg --dearmor 

| sudo tee /usr/share/keyrings/nginx-archive-keyring.gpg >/dev/null
Setup repository
echo "deb [signed-by=/usr/share/keyrings/nginx-archive-keyring.gpg] 

http://nginx.org/packages/ubuntu lsb_release -cs nginx" 

| sudo tee /etc/apt/sources.list.d/nginx.list
Update and install
sudo apt update
sudo apt install nginx -y

3.2. Install on CentOS/RHEL

Method 1: From EPEL repository

# CentOS 7
sudo yum install epel-release -y
sudo yum install nginx -y

CentOS 8 / Rocky Linux / AlmaLinux
sudo dnf install nginx -y
Start and enable
sudo systemctl start nginx
sudo systemctl enable nginx
Open firewall
sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --permanent --add-service=https
sudo firewall-cmd --reload

Method 2: From official Nginx repository

# Create repo file
sudo tee /etc/yum.repos.d/nginx.repo <<EOF
[nginx-stable]
name=nginx stable repo
baseurl=http://nginx.org/packages/centos/\$releasever/\$basearch/
gpgcheck=1
enabled=1
gpgkey=https://nginx.org/keys/nginx_signing.key
module_hotfixes=true
EOF

Install
sudo yum install nginx -y

3.3. Install on macOS

Using Homebrew:

# Install Homebrew (if not already installed)
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Install Nginx
brew install nginx
Start Nginx
brew services start nginx
Or run in foreground
nginx
Check
nginx -v

Paths on macOS:

• Config: /usr/local/etc/nginx/nginx.conf
• Document root: /usr/local/var/www
• Logs: /usr/local/var/log/nginx

3.4. Install on Windows

Step 1: Download

• Visit: http://nginx.org/en/download.html
• Download the Windows version (nginx-x.x.x.zip)

Step 2: Extract and run

# Extract to C:\nginx

Open Command Prompt as Administrator
cd C:\nginx
Start Nginx
start nginx
Or
nginx.exe

Managing Nginx on Windows:

# Check version
nginx -v

Test configuration
nginx -t
Stop
nginx -s stop
Reload
nginx -s reload
Quit gracefully
nginx -s quit

Note: On Windows, Nginx is less stable than on Linux and should not be used in production.

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4. Directory Structure and Basic Configuration Files

4.1. Directory structure on Ubuntu/Debian

/etc/nginx/
├── nginx.conf                 # Main configuration file
├── mime.types                 # MIME type definitions
├── fastcgi_params            # FastCGI parameters
├── proxy_params              # Proxy parameters
├── sites-available/          # Available site configurations
│   └── default              # Default virtual host
├── sites-enabled/            # Symlinks to active sites
│   └── default -> ../sites-available/default
├── conf.d/                   # Additional configurations
├── modules-available/        # Available modules
└── modules-enabled/          # Enabled modules

/var/log/nginx/
├── access.log                # Access logs
└── error.log                 # Error logs
/var/www/html/                # Default document root
└── index.nginx-debian.html
/usr/share/nginx/html/        # Alternative document root

4.2. Directory structure on CentOS/RHEL

/etc/nginx/
├── nginx.conf                # Main configuration file
├── mime.types
├── fastcgi_params
├── conf.d/                   # Virtual host configs
│   └── default.conf
└── default.d/

/var/log/nginx/
├── access.log
└── error.log
/usr/share/nginx/html/        # Document root
└── index.html

4.3. Basic nginx.conf configuration file

# User running Nginx
user www-data;

Number of worker processes (usually = number of CPU cores)
worker_processes auto;
PID file
pid /run/nginx.pid;
Load dynamic modules
include /etc/nginx/modules-enabled/*.conf;
events {
# Maximum connections per worker
worker_connections 768;
# Event method (epoll for Linux)
use epoll;

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

##
# Logging Settings
##
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;

##
# Gzip Settings
##
gzip on;
gzip_disable "msie6";

##
# Virtual Host Configs
##
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;

}

4.4. Sample Virtual Host file

server {
# Listening port
listen 80;
listen [::]:80;

# Domain name
server_name example.com www.example.com;

# Document root
root /var/www/example.com;
index index.html index.htm;

# Access and error logs
access_log /var/log/nginx/example.com.access.log;
error_log /var/log/nginx/example.com.error.log;

# Location block
location / {
    try_files $uri $uri/ =404;
}

# Deny access to .htaccess
location ~ /\.ht {
    deny all;
}

}

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5. Starting, Stopping, and Reloading Nginx

5.1. Manage with systemctl (Linux)

# Start Nginx
sudo systemctl start nginx

Stop Nginx
sudo systemctl stop nginx
Restart Nginx
sudo systemctl restart nginx
Reload configuration (no downtime)
sudo systemctl reload nginx
Check status
sudo systemctl status nginx
Enable auto-start on boot
sudo systemctl enable nginx
Disable auto-start
sudo systemctl disable nginx

5.2. Manage with nginx command

# Test configuration (very important before reloading)
sudo nginx -t

Test and show config
sudo nginx -T
Reload configuration
sudo nginx -s reload
Stop gracefully (wait for current requests to finish)
sudo nginx -s quit
Stop immediately
sudo nginx -s stop
Reopen log files (after log rotation)
sudo nginx -s reopen
View version and compile options
nginx -V

5.3. Difference between reload, restart, and stop

reload:

• No downtime
• Nginx re-reads the configuration
• Old worker processes finish their current requests then shut down
• New worker processes are created with the new configuration
• Use when: Changing configuration, adding/modifying virtual hosts

sudo nginx -s reload

or
sudo systemctl reload nginx

restart:

• Has downtime (brief)
• Fully stops then starts again
• All connections are dropped
• Use when: Installing new modules, major changes

sudo systemctl restart nginx

stop vs quit:

# Stop immediately (kill connections)
sudo nginx -s stop

Quit gracefully (wait for requests to finish)
sudo nginx -s quit

5.4. Checking that Nginx is running

# Check process
ps aux | grep nginx

Check listening ports
sudo netstat -tulpn | grep nginx
or
sudo ss -tulpn | grep nginx
Check version
nginx -v
Test access
curl http://localhost
or
curl -I http://localhost

5.5. Basic Troubleshooting

Error: nginx.conf test failed

# Check detailed error
sudo nginx -t

View error log
sudo tail -f /var/log/nginx/error.log

Error: Port 80 already in use

# See which process is using port 80
sudo lsof -i :80

or
sudo netstat -tulpn | grep :80
Kill the process if needed
sudo kill -9 <PID>

Error: Permission denied

# Check user in nginx.conf
grep user /etc/nginx/nginx.conf

Check directory permissions
ls -la /var/www/html
Fix ownership
sudo chown -R www-data:www-data /var/www/html

Cannot access via browser:

# Check firewall (Ubuntu/Debian)
sudo ufw status
sudo ufw allow 'Nginx Full'

Check firewall (CentOS)
sudo firewall-cmd --list-all
sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --reload
Check SELinux (CentOS)
sudo getenforce
sudo setenforce 0  # Temporarily disable to test

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6. Practice Exercises

Exercise 1: Install and verify

1. Install Nginx on your operating system
2. Check the version and status
3. Visit http://localhost and view the default welcome page
4. Find and view the access.log file

Exercise 2: Get familiar with commands

1. Test configuration: nginx -t
2. Reload Nginx
3. Stop and restart Nginx
4. Check running processes

Exercise 3: Explore the directory structure

1. Open nginx.conf and read the directives
2. Find the document root in the default virtual host
3. Create a simple HTML file in the document root
4. Access the file via browser

Exercise 4: Intentional error fixing

1. Add an invalid syntax line to nginx.conf
2. Run nginx -t to see the error
3. Fix the error and test again

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Summary

In this lesson, you learned:

• ✅ What Nginx is and its event-driven architecture
• ✅ Nginx vs Apache comparison
• ✅ Installing Nginx on multiple operating systems
• ✅ Directory structure and configuration files
• ✅ Basic Nginx management commands

Next lesson: We will dive deeper into Nginx configuration, exploring contexts, directives, virtual hosts, and serving static files.