[svlug] Multiple Web Servers on One IP

[Luke S Crawford]

"Sargun Dhillon" <xbmodder at gmail.com> writes:
> Uhm. some VPS providers run modified kernels that you cannot add your
> own swap under (even xen!). Also, swap is slow sucks, etc.. Swap
> thrashes you.

I've not heard of a xen provider doing that... it is possible, 
but I don't see what the provider would gain from doing so.  I mean,
your swap would come out of your existing disk allocation,
so I don't see why the provider would care if you used your disk allocation
for swap vs, say, a database.  

Many Xen hosts let you install your own kernel with PyGrub, though, 
and in that case, it would be impossible for them to stop you from 
using swap.
 
having swap allocated is fine;   If you have swap allocated, but it's
not swapping in or out (check the 'si' and 'so' values in vmstat)  
then swap is giving you ram without a performance penalty.  (well, until
it needs to swap that memory back in-  in some applications, though,
swap, along with a decent memory manager, can  give you a significant
performance boost by freeing up ram for disk cache.)  

Swap is great for the situation where you have a large blob of memory
allocated, but you mostly access a small portion of that memory (such as
in the case of using a giant apache mod_* binary to serve static html.) 

In the optimal situation, swap is a nice system-level hack to work around 
programs that allocate and hold memory that is seldom accessed.   

In the suboptimal situation, it means that your applications run slow rather
than crashing.  Either way, I think it's a win.  

> Also from chris' prior email:
> 
> I do not want to use any non-80 ports, since I do not want to run into
> a restrictive firewall.  I also don't want to run into any possible
> issues that may be caused by serving non-SSL pages and files through
> the SSL port (which would solve the problem and circumvent the wrath
> of the firewalls, but I may need SSL later, too!)

Ah.  right then.  I should pay attention or shut up.  :)