[mistwang]

To reload a RoR app, currently i use capistrano to restart mongrel processes, very simple, and it won't affect other vhost. how is it done using LSAPI, disable/enable vhost, or restart whole webserver?

For LSWS + Ruby LSAPI, just restart LSWS, restart is graceful, no downtime at all.

under which scenario would one use LSRR instead of LSAPI? I mean what LSRR attempt to accomplish that LSAPI can't do?

LSRR is implemented on top of LSAPI, it is for running plain CGI scripts written in Ruby.

If traffic grows, I think I can still use one LS vhost to load balance more mongrel processes on several servers, correct? how is scalability done using LSAPI cross several servers?

Yes, you can do that. In that case, I would recommend running LSWS + LSAPI on each every cluster node with a front-end load balancer. It should be easier to setup than running LSAPI on a node along, faster than using Mongrel, and pages cached in file system on a node can served by LSWS directly.

For how to use capistrano together with LSWS + LSAPI in a cluster, please read the discussion in
http://www.litespeedtech.com/support/forum/showthread.php?t=522&page=2