What are the differences? What are the advantages of litespeed over apache? Any experience on both?
I use LiteSpeed as my primary webserver. It more or less replaces Apache in most functionality (including rewrites and bytelogging), will drop directly in with CPanel/WHM. It has an extensive featureset really designed for performance and scalability (and DDoS mitigation). The web interface is nice versus digging through configuration files. My favorite feature is the PHP SAPI module they provide which increases PHP performance. I really find LiteSpeed to be a refreshing change from Apache and gives me only the functionality I need to host my personal sites. There is a downside however, Litespeed costs money. The standard version is free (which is what I use), but it caps max concurrent connections. One of my sites is active with hundreds of simultaneous users and I never run into concurrency problems.
I would say LiteSpeed's strength lies in static fileserving and dynamic content with either Python, PHP, or Ruby (especially Ruby on Rails). In older benchmarks it performs better which in my experience is true, but at the same time tuning Apache can get close to similar results, but the LSAPI module is pretty unique (similar to fast-cgi) and works well. The main developer is really attentive and implemented a few things I needed in LiteSpeed.
I'd say give it a try. It can import your existing Apache configuration and run on an offset port and is free unless you need the Enterprise edition.
This is really an update so that folks arriving at this question aren't misled.
The reason was simply this:
Like most popular PHP applications, WordPress is written for Apache, which serves more than half of the web. However, WordPress.com sysadmins got sick of Apache crashing at super high workloads and especially when deploying configuration changes. So they chose a superfast and superstable server (LiteSpeed) which is Apache compatible - i.e. is a drop-in replacement, i.e. just simply works using Apache settings including virtual hosts and .htaccess files.
The problem was that LiteSpeed was commercial, and WordPress felt some pressure to live up to its OpenSource ideals (LiteSpeed was commercial....a much more limited "Standard" edition was available for free). So, in 2008 WordPress.com moved to nginx and WordPress.org dropped its LiteSpeed recommendation.
In mid-2013, OpenLiteSpeed was released as an open source edition of the web server. Compared to LiteSpeed Enterprise (the commercial edition), OpenLiteSpeed does not have 100% Apache compatibility (e.g. .htaccess is not supported, Apache rewrite rules are supported but must be copy-pasted from .htaccess into the config), control panels support (can't have cPanel, Plesk, VirtualMin etc on OpenLiteSpeed), mod_security compatibily and page cache (Enterprise edition has page cache for static content while OpenLiteSpeed doesnt...though OpenLiteSpeed can be used with Varnish so this is not a major hurdle).
So, with that background, the advantages of LiteSpeed over Apache:
- It is generally believed that most servers, including Apache, nginx and LiteSpeed are mostly comparable in performance of dynamic content.
- At very high concurrencies, LiteSpeed is faster than nginx which is faster than Apache.
- LiteSpeed and nginx are fantastic (and way ahead of Apache) at serving static content.
- OpenLiteSpeed is really adopting some new, cool stuff like Google's SPDY protocol while Apache lags in implementation.
- LiteSpeed will also likely use a fraction of the resources that Apache uses for the same load...
Looks like WordPress.com is using varnishd, pound, Amazon S3, and an unnamed 'http daemon' : http://blog.apokalyptik.com/2007/10/10/so-you-wanna-see-an-image/