[K12OSN] TeacherTool and dhcpd load balancing.

Robert Arkiletian robark at gmail.com
Wed Mar 21 16:16:37 UTC 2007

On 3/21/07, Jim Kronebusch <jim at winonacotter.org> wrote:
> On Tue, 20 Mar 2007 22:18:57 -0700, Robert Arkiletian wrote
> > On 3/20/07, Krsnendu dasa <krsnendu108 at gmail.com> wrote:
> > > I have successfully set up dhcpd load balancing. Now when I run
> > > TeacherTool I can only see the students logged into the same server as
> > > me. Is there a way to see all users that are logged on including
> > > students on the other ltsp server?
> >
> > Currently what others in your situation are doing is running FreeNX on
> > one server and connecting to it from the other server. So you launch
> > two instances of fl-teachertool in separate windows. It's not the best
> > solution but it works for now.
> If all users booted from the same boot server, but pulled apps from different app
> servers, would TeacherTool still pick up all users and all processes?  I am guessing

I think it would pick up the username and ip's but not all the processes.

> that TeacherTool only picks up processes show as running on the server it is running from?


> How does TeacherTool find users and processes?  Say you had 3 servers in your load

I use this line to find user id's and ip's

netstat -t -e -n|grep :6000| grep ESTABLISHED |sed -e 's/:/ /g'| sed
-e 's/ESTABLISHED/ESTABLISHED /' | awk '{print $9,$6}'|sort|uniq

The last sed is for the difference in the way Debian and Fedora
netstat output is displayed.
BTW if you are using a system that is not using english you have to
modify the above line since the word ESTABLISHED will appear in a
different language. I will try to fix this in my next version. Someone
suggested I use LANG=C netstat...
Once I have all uid's which I can then change into usernames. I
collect processes in a loop for each user like this

ps --User username -o  pid,rss,comm --sort -rss

> balance cluster.  Could an ssh tunnel be setup in all directions from server to server
> so that no matter which server you ran your teacher tool from you could get a list of
> logged in users and running apps from another server?

It's possible to do that. You would have to setup root ssh-keys
without a passphrase. But some things would break. Big problem would
be broadcasting, which is the best feature of fl-tt (in my opinion).
You can only run one session of vncreflector (which server?). Pick
one. Now I have to ssh into the other server launch vncviewer for each
user that connects to an ip OUTSIDE the lan of that server. So in
addition to setting up fl-tt, which people sometimes have trouble with
you're going to have firewall issues since vncviewer has to get
through BOTH server firewalls. Not to mention the huge ip traffic
that's going to get created through eth1 and one of the NAT servers. I
guess what I'm saying is I'm not sure if it's worth doing if there are
not that many people using load balancinng. And anyone who is, is
probably not using more than 2 servers. So by using FreeNX you can
have a quick fix. That said, if anyone is willing to hack on my code I
would be willing to provide some guidance. The new feature I'm going
to concentrate on now is the vncsnapshot window.

Robert Arkiletian
Eric Hamber Secondary, Vancouver, Canada
Fl_TeacherTool http://www3.telus.net/public/robark/Fl_TeacherTool/
C++ GUI tutorial http://www3.telus.net/public/robark/

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