Re: [K12OSN] Question about multiple servers...

Hans Ekbrand (hans@sociologi.cjb.net)
Fri, 11 Oct 2002 10:22:01 +0200 


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> > So, given my probably overly-detailed explanation, what would be the=20
> > best way to cluster these three servers. Should I give each it on=20
> > unique switch and separate the lab into three groups, one for each=20
> > server. Should I use Mosix to cluster the three servers together (my=20
> > knowledge on Mosix is limited, but I'm definitely willing to go this=20
> > route if it yields the result I want). Should I have all three share a=
=20
> > switch and then use some sort of DHCP/MAC Address trick to make sure=20
> > that the 40 clients get spread across the 3 servers. Or am I looking at=
=20
> > this in completely the wrong way and is there a better way to do this?

On Thu, Oct 10, 2002 at 09:28:51PM -0700, James Jensen wrote:
> In any case, IMHO, I would suggest the following cluster scenario for your
> servers (based as it is on my limited experience in openMosix):

As several other have pointed out in the tread about the real benefit
of mosix-clusters, typical LTSP applications (OO, browsers) don't tend
to migrate.

Therefore, I would suggest other means of load-balancing. I have had
an email exchange with Tom Lisjac  on this. He
might have some working config files for you to copy.

1. Load-balance at boot time. (and get take-over at the same time)

The latest version of dhcpd3, 3.0.1rc9, has built in support for
combined load-balancing and fall-over functions. Basically you have to
identical servers, that only differs in hostname, ipnumber and that
one of them is defined as the primary dhcpd. Use the hba option in
dhcpd.conf to get fine graid load balancing. (NB. if you use the
default kernels with initrd from LTSP, then the split option in dhcpd
will not do what you want, since every terminal does TWO dhcpd calls
one server will get all terminals)

2. Load-balance at XDMCP time.

Change the following lines in /opt/ltsp/i386/etc/rc.local. Substitute
"-query" with "-broadcast"
=20
     if [ -w /proc/progress ]; then
         echo "/usr/X11R6/bin/${XBINARY} ${ACC_CTRL} -query
     ${XDM_SERVER} >/dev/tty3 2>&1" >/tmp/start_ws
     else
         echo "/usr/X11R6/bin/${XBINARY} ${ACC_CTRL} -query
     ${XDM_SERVER}" >/tmp/start_ws
     fi
=20
This way the servers will compete on the XDMCP call, and likely the
least loaded one will answer first and thus win the client. AFAIK no
changes in the Xaccess file should be necessary.

Optionally you could set up a third (and more) server, but don't run
dhcpd/tftpd/nfsd on it, just a display manager, The reason you cannot
use three (or more) alternate dhcpds is that dhcpds built-in take-over
function cannot be used with more than two servers. Since all servers
are on the same subnet, network bandwidth will probably eventually be
the bottleneck.

Good Luck.

--=20

Hans Ekbrand
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