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

-> 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

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.


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
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,


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