Hi Chuck!
I am in the idea stage for something I am not positive is entirely worth the
effort and I am in totally uncharted territory.
I am not sure what terminology is i am looking for here...
Virtual servers, load balancing, fail over, high availability to name a
few ;)
what i am thinking i want to do is:
have 2 hosts one a mirror of the other including all vserver guests etc. the 2
machines are identical in every way.
rather than have the mirror machine on 'standby' waiting for some fateful day
it is needed, i would like both servers and all guests to be running
simultaneously. this would be accomplished by having everything running
unique private network ip addresses. this would allow adding
additional 'mirror' machines as necessary.
the existing public ips from the production server we have running would be
moved to some 'control' computer which would have a listing of the private
ips that would serve what the public ip wants and would call on either one as
needed. if one of the private ip servers doesnt respond (down) the control
computer would simply choose the working ip until the first one comes back
online.
what do i need to do in the 'control' machine to accomplish this? is this some
kind of configuration that already exists in the linux distro? we run gentoo.
beowolf (whatever that is)?
For the fail over or even load balancing in the future, have a look at
the Linux Virtual Server project [1]. Probably the NAT approach [2]
suits you best (as you want to use private IP addresses).
is there another way of accomplishing what i wish to do? also how messy will
keeping the mirror machines 'in sync' be? would i be better off having all
machines but the controller share a common nfs mount for all the guests?
Well it depends on what services you're going to run. If you want an
active-passive setup (only one backend-servers is running at the same
time) you "can" use NFS. However there are some services which are a
little bit hairy to play nice with NFS mounts. Otherwise you can sync
your data on the service level ~ replication (if the service provides
the ability to do so). Last but not least DRBD block devices [3] is an
option to keep machines in sync on the block device level.
If you want to achieve an active-active setup consider to use some sort
of SAN or DRBD running with a cluster file system like OCFS2 [4] or GFS
[5] (to prevent locking and other issues).
some of these virtual servers are very high volume usage so if all the data
must route through the control computer, i am thinking that computer would
have to be a monster. or maybe have several control computers each handling a
different class of service.
I don't think they have to be a monster ;) However a fair amount of
RAM would not be amiss.
sorry if i sound like i have no clue what i am talking about, but that is the
truth :) , i only think i know what i want to accomplish.
I'm sure there are other ways to accomplish this (Hardware load
balancers etc.), nonetheless I hope I gave you some pointers in the
right direction. Remember that this isn't the sort of setup which is up
and running in 15min.
Good luck and regards
Chris
[1] http://www.linuxvirtualserver.org/
[2] http://www.linuxvirtualserver.org/VS-NAT.html
[3] http://www.drbd.org/
[4] http://oss.oracle.com/projects/ocfs2/
[5] http://www.redhat.com/software/rha/gfs/
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