In the May 2013 survey we received responses from 672,837,096 sites, which is 23.8M more than last month.

Apache had the largest growth this month, gaining 28.3M websites and increasing its market share by 2.41 percentage points to 53.4%. The majority of this growth was attributable to Apache Traffic Server (ATS), which gained 28M websites and increased its market share from 0.03% to 4.2%. Nearly all of the Apache Traffic Server growth occurred at Go Daddy — 75% of websites hosted by Go Daddy now use ATS and Go Daddy now hosts 99% of all sites using this server software.

Originally created as a commercial product by Inktomi in 1997, Apache Traffic Server is an extensible multi-threaded event-driven caching proxy server which is claimed to scale well on modern multi-core systems. Yahoo! acquired Inktomi in 2005, and in November 2009, the project was donated to the Apache Software Foundation.

The vast majority of the ATS served websites at Go Daddy were previously served by Microsoft IIS, resulting in the rather noticeable loss of 3.26 percentage points of market share. Microsoft IIS's market share is now 16.7%. Despite the loss at Go Daddy it gained more new sites than any competitor this month, with 43% of all new websites being served on Microsoft IIS, while accounting for only 30% of expired websites (this includes inactive blogs, as well as sites which no longer exist).

nginx reached a new milestone this month: it is now used by more than 100M websites, and within the Million Busiest Websites has overtaken Microsoft IIS to take second place with a market share of 13.5%. Overall, nginx's market share now stands at 15.5%, just 1.2 percentage points behind Microsoft, helped by a growth of 8.3M sites this month.

The latest stable version, nginx 1.4.0, was released last week, integrating OCSP stapling and experimental SPDY draft 2 support. nginx is used extensively by the WordPress.com blog hosting service, whose owners – Automattic – sponsored development of the ngx_http_spdy_module. Development of OCSP stapling support was sponsored by Comodo, DigiCert, and GlobalSign.

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