Re: [Xen-users] Few Questions / Application of Xen

["M.A. Williamson" <maw48@xxxxxxxxx>]

> -> How is it possible to load balance virtual machines between
> physical hosts ? And more generally is it possible to
> interconnect/autodiscover a network of physical hosts (like OpenMosix
> for example) ?
> On the RedHat flash on virtualization, it seems possible...
Currently you need to do this manually. More powerful automatic load 
balancers are likely to appear on the market at some point, as an 
additional management product.
It should be possible to script some sort of basic management application 
that would suit your needs, however.
> -> How is it possible to manage the fail over ?  (like physical host A
> is down, let's migrate its virtual machines to physical host B for
> example)
Two aspects: for a planned shutdown you'd want the management software to 
live migrate domains off a server you were planning to take down. You'd 
also like it to detect a crash, and reboot the domains on other hosts (and 
lock out the downed server from shared storage so that if it comes back on 
the network any remaining domain images it's running can't confuse the 
situation)
> -> Is it possible to "burst" RAM usage ?
You can change the RAM footprint using xm mem-set (or something like that). 
Again, this is manual but it's possible in principle to script a tool that 
will automatically allocate memory to a domain which is swapping more, and 
revoke memory from domains with low swap activity.
Again, this is a management plane function that isn't provided by the 
current set of tools, but it is possible to write in principle.
HTH,
Mark

> Here's my more general problem, I would like to host game servers
> (Quake, Counter Strike, etc...) applications....
> The common problem with hosting those servers, is that most of the
> time they are not used, so basically you have to load balance the
> servers by hand (like putting 8 game servers per machine and that's
> all)... so you have a lot of manual work to do... and you can't really
> balance correctly the load amongst the server (eg : a machine can have
> 7 servers out of 8 who are running with players, another one totally
> free, etc...)....
>
> That's why I was looking at cluster solutions....
>
> I first started with Single System Image clusters like OpenMosix and
> OpenSSI, but I don't really think the way socket migration is handled
> is correct for such I/O and Network intensive applications... maybe I
> am wrong.... but from what I've read the socket has to stay on the
> first  machine..... so it could lead to a saturation of the NIC.
>
> That's why I ended with Xen, I could basically set up one server per
> virtual machine, and migrate the virtual machine amongst the physical
> servers to load balance, the only problem is that I can't predict how
> much RAM a virtual machine could take, if there is 0 players the
> process is quite lite, is there are tons of players it can be quite
> heavy....
> And setting 256M of RAM per virtual machine just to be sure, would be
> a total waste of memory....
>
> If you have any ideas that would help :),
>
> Thanks a lot,
>
> Ugo PARSI
>
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