Depending on who you ask, Nginx is either the second- or third-most widely used Web server. But among the most heavily trafficked sites, it's headed straight to the top.
Originally released in 2002, the open source server was created to address problems associated with high-volume Web traffic, such as heavy CPU load or memory consumption. Apache's HTTPD server has long been the default choice for most Web hosts, but Nginx's speed and economy have been steadily winning over a growing share of sites from all corners of the Web.
The most tangible example of Nginx's growing dominance can be seen in Netcraft's latest chart of Web server stats for the top million busiest sites. Since late 2008, Nginx's market share has risen steadily, matching Apache's decline almost one-for-one. The other major competitor, Microsoft IIS, has seen its share of the top sites slowly decline by about half over the course of the last six years. Google has remained consistently flat as a source of traffic for that top million.
With Netcraft's total market share for all Web servers, the spread is markedly different. Apache still show a steep plunge with no end in sight, but Nginx's growth is far flatter. Rather, Microsoft and Google show the greatest growth over the last couple of years. Some of Microsoft's gain may be attributable to the growth of Azure, where IIS is used as the Web serving infrastructure for applications hosted there. (Virtual machines within Azure that don't run Windows are bound to use something else -- Apache or Nginx, most likely -- so that may further skew the results.)
Proof of Nginx's growth among top sites can also be found courtesy of W3Techs, another aggregator of Web server statistics. That group lists Nginx even higher in the rankings overall than Netcraft: Apache claims 59.1 percent, Nginx at 22.5 percent, and Microsoft IIS at 13.5 percent. And of the top 1,000 sites in the W3Techs ranking, Nginx holds the lead at a whopping 42.1 percent; for the top million, it's 25.1 percent.
Some top sites are not likely to ever use Nginx because they are unlikely to use any third-party Web server. Facebook, for instance, opted to roll its own Web stack, Proxygen. That said, the odds are low that a significant percentage of the top websites will do the same -- not everyone faces problems of the same magnitude as Facebook.
One statistic that remains unclear, and could shed light on how Nginx is being adopted by heavily trafficked sites, is what percentage of the sites using Nginx are opting for the BSD-licensed open source version over the commercial version with enterprise-level features.
Nginx launched the commercial version as a way to finance further development of the underlying project, but the move has coarsened a few hairs with those worried about possibly comprising the project's open source roots. On the whole, it doesn't seem to have hurt Nginx's base popularity.