Re: [Vserver] clusters/farms/failovers?

From: Christian Affolter <c.affolter_at_stepping-stone.ch>
Date: Thu 21 Jun 2007 - 08:14:29 BST
Message-ID: <467A2555.1060008@stepping-stone.ch>

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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Received on Thu Jun 21 09:02:13 2007

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