nginx (pronounced as 'engine x') is a powerful HTTPWeb server/reverse proxy and IMAP/POP3 reverse proxy. According to a survey conducted in December 2008 by Netcraft, nginx has grown significantly and has surpassed lighttpd (also known as Lighty). Because of its small memory footprint and high scalability, nginx has found tremendous usage in virtual private servers (VPS).

A reverse proxy is a front end to one or more Web servers. All connections originating from the Internet and destined for Web servers (behind the reverse proxy) are routed through the proxy. Based on the configuration, the proxy may decide to serve the request itself or pass it either partially or totally to one of the member Web servers behind it. In this manner, the reverse proxy presents a single interface for a set of server. to the caller. A reverse proxy can thus work as a load balancer distributing the incoming load to member servers. It can also cache th€ contents being served.

The architecture: A layered approach

I typically use Debian or RHEL in my serve and try to stick with the packages available in the base distribution as far as possible. For the purpose of this article, I will use four Debian Etch servers and will divide the entire set-up into two layers. The first layer (Layer 1) will have a pair of highly-available (using Heartbeat) nginx reverse proxy installations that will be used to load balance the Web servers located in the second layer (Layer 2). In Layer 2,

I will set up two nginx installations that serve websites, including PHP pages. Instead of two, you can of course have as many Web servers as required. The number of Web servers should be dependent on the total load on the servers. If you feel that the load on the servers is increasing, you can easily add another Web server to the cluster.

In addition to this, there can be a third layer (Layer 3) of database servers. The database is typically used by the applications running on the Web/application servers, where the application directly makes a call to the database using an appropriate method. Database clustering has a slightly different approach and we will take up this subject at a later date. Also, the database layer is independent of our current configuration, and can be added and removed at will without impacting the current set-up.

The installation method of nginx is identical on all the four servers in our set-up. From the configuration perspective, the Layer 1 reverse-proxy servers will have ide?tical active-passive configurations and the Layer 2 Web servers will have identical configurations.

The Debian Etch has quite a dated version of nginx, but it is good enough for our purposes. So I have decided to stick with this old but stable version. In order to install nginx in Debian Etch, issue the following command as the root user: