Nginx: the High-Performance Web Server and Reverse Proxy

Apache is the most popular Web server and one of the most successful open-source projects of all time. Since April 1996, Apache has served more Web sites than any other Web server. Many of the world's largest Web sites, including YouTube, Facebook, Wikipedia and Craigslist, use Apache to serve billions of page views per month. Over the years, Apache has proven itself to be a very stable, secure and configurable Web server. Although Apache is an excellent Web server, what if there were an alternative with the same functionality, a simpler configuration and better performance? That Web server exists, and it's called Nginx.

Nginx, pronounced “Engine X”, is a high-performance Web server and reverse proxy. It was created by Igor Sysoev for www.rambler.ru, Russia's second-largest Web site. Rambler has used Nginx since summer 2004, and it's currently serving about 500 million requests per day. Like Apache, Nginx is used by some of the largest Web sites in the US, including WordPress (#26), YouPorn (#27), Hulu and MochiMedia. As of May 2008, Nginx is the fourth-most-popular Web server, and it is currently serving more than two million Web sites. As it is only trailing behind Apache, IIS and GFE, it is effectively the second-most-popular Web server available for Linux.

Like Apache, Nginx has all the features you would expect from a leading Web server:

It is stable, secure and very easy to configure, as you will see later in the article. However, the main advantages of Nginx over Apache are performance and efficiency.

I ran a simple test against Nginx v0.5.22 and Apache v2.2.8 using ab (Apache's benchmarking tool). During the tests, I monitored the system with vmstat and top. The results indicate that Nginx outperforms Apache when serving static content. Both servers performed best with a concurrency of 100. Apache used four worker processes (threaded mode), 30% CPU and 17MB of memory to serve 6,500 requests per second. Nginx used one worker, 15% CPU and 1MB of memory to serve 11,500 requests per second.

Nginx is able to serve more requests per second with less resources because of its architecture. It consists of a master process, which delegates work to one or more worker processes. Each worker handles multiple requests in an event-driven or asynchronous manner using special functionality from the Linux kernel (epoll/select/poll). This allows Nginx to handle a large number of concurrent requests quickly with very little overhead. Apache can be configured to use either a process per request (pre-fork) or a thread for each request (worker). Although Apache's threaded mode performs much better than its pre-fork mode, it still uses more memory and CPU than Nginx's event-driven architecture.

Nginx is available in most Linux distributions. For this article, I use Ubuntu 8.04 (Hardy), which includes Nginx version 0.5.33. If your distro does not have Nginx, or if you want to run a newer version, you always can download the latest stable version (v0.6.31 at the time of this writing) and install from source.

Run the following command as root to install Nginx:

# apt-get install nginx

Now that Nginx is installed, you can use the startup script to start, stop or restart the Web server:

# /etc/init.d/nginx start
# /etc/init.d/nginx stop
# /etc/init.d/nginx restart 

Most configuration changes do not require a restart, in which case you can use the reload command. It is generally a good idea to test the Nginx configuration file for errors before reloading:

# nginx -t
# /etc/init.d/nginx reload

Let's go ahead and start the server:

# /etc/init.d/nginx start

Nginx now should be running on your machine. If you open http://127.0.0.1/ in your browser, you should see a page with “Welcome to nginx!”.

Now that Nginx is installed, let's take a look at its config file, located at /etc/nginx/nginx.conf. This file contains the server-wide settings for Nginx, and it should look similar to this:

user www-data;
worker_processes  1;
error_log  /var/log/nginx/error.log;
pid  /var/run/nginx.pid;
events {
  worker_connections  1024;
}
http {
  include  /etc/nginx/mime.types;
  default_type  application/octet-stream;
  access_log  /var/log/nginx/access.log;
  sendfile  on;
  keepalive_timeout  65;
  tcp_nodelay  on;
  gzip  on;
  include /etc/nginx/sites-enabled/*;
}

We are not going to change any of these settings, but let's talk about some of them to help us understand how Nginx works. The worker_processes setting tells Nginx how many child processes to start. If your server has more than one processor or is performing large amounts of disk IO, you might want to try increasing this number to see if you get better performance. The worker_connections setting limits the number of concurrent connections per worker process. To determine the maximum number of concurrent requests, you simply multiply worker_processes by worker_connections.

The error_log and access_log settings indicate the default logging locations. You also can configure these settings on a per-site basis, as you will see later in the article. Like Apache, Nginx is configured to run as the www-data user, but you easily can change this with the user setting. The startup script for Nginx needs to know the process ID for the master process, which is stored in /var/run/nginx.pid, as indicated by the pid setting.

The sendfile setting allows Nginx to use a special Linux system call to send a file over the network in a very efficient manner. The gzip option instructs Nginx to compress each response, which uses more CPU but saves bandwidth and decreases response time. Additionally, Nginx provides another compression module called gzip precompression (available as of version 0.6.24). This module looks for a compressed copy of the file with a .gz extension in the same location and serves it to gzip-enabled clients. This prevents having to compress the file each time it's requested.

The last setting we are concerned with is the include directive for the sites-enabled directory. Inside /etc/nginx, you'll see two other directories, /etc/nginx/sites-available and /etc/nginx/sites-enabled. For each Web site you want to host with Nginx, you should create a config file in /etc/nginx/sites-available, then create a symlink in /etc/nginx/sites-enabled that points to the config file you created. The main Nginx config file includes all the files in /etc/nginx/sites-enabled. This helps organize your configuration files and makes it very easy to enable and disable specific Web sites.