[Phpwm] Load Balancing and redundancy

[David Goodwin]

> http://www.linux.com/article.pl?sid=05/07/27/1729229
> 
> that makes it sound amazingly easy. 
> 
> The things I'm not sure about are:
> 
> Redundancy - It can handle one of the web servers going down but what
> happens if the balance server goes down?
> 

With LVS you can protect the routing server with e.g. Heartbeat... but 
you effectively then have a minimum cluster size of 4, (2 routers, 2 web 
servers). Perhaps availability isn't a great issue?

Does : http://bytemark.co.uk/page/Live/hosting/cluster/ help?

> Resources - I guess you need to have an exact copy of the site on each
> server which sounds like a headache. Linux Virtual Server utilizes a shared
> data store so gets around this.

Well, I don't think it would be that much of a pain. I presume you use 
some sort of versioning system (CVS, SVN etc) - so the code should be in 
sync already. Your main issue is that of sessions (and e.g. uploaded 
files). Both would need to be stored in a database, or on a shared file 
system like NFS.

(How does rsync handle deletion when a file could appear on either server?)

My gut reaction is to go for the easier 'move db to seperate box' to 
start with, as it's easy to do, with no headaches involved - although a 
cross over cable between db <-> web server would be nice.

David.


-- 
David Goodwin

[ david at codepoets dot co dot uk ]
[ http://www.codepoets.co.uk       ]