[FreeNX-kNX] Load balancing with FreeNX

[Prakash Velayutham]

Hi,

I have the sessions in a shared NFS area now (just the db part and not
the home), but I still see issues with the load-balancing. Could you
please explain a little more about your setup? Here is mine.

frontier (load-balancer)
headnode (NXserver1)
cellulose (NXserver2)
protein (NFS server)

All systems running OpenSUSE - 10.2 with NX-1.5.0-73 and FreeNX 0.6. I
have copied the /var/lib/nxserver/db folder from one of the machines
upto the NFS server and set the uid, gid as required.
I have mounted this shared folder in all the systems under
/var/lib/nxserver/db. Only nx user or anyone from root group is able to
write to this folder now.

I have set up round-robin load-balancing algo in frontier. I have added
the 2 load-balanced NX servers in frontier's node.conf like this.

SERVER_LOADBALANCING="Yes"
LOAD_BALANCE_SERVERS="headnode.chmccorp.cchmc.org cellulose.cchmc.org"
LOAD_BALANCE_ALGORITHM="round-robin"

I will set it to "load" once I get this simple setup working.

Now if I start a client session to connect to frontier, I can see that
the sessions gets started in cellulose transparently. I can also see
that the corresponding files get created in the shared NFS area.

protein:~ # ls -al /home/var/lib/nxserver/db
total 24
drwxr-xr-x  5 vdr  root 4096 Jun 22 10:06 .
drwxr-xr-x  3 root root 4096 Jun 22 10:00 ..
drwx------  2 vdr  root 4096 Jun 22 10:00 closed
drwx------  2 vdr  root 4096 Jun 22 10:00 failed
-rw-r--r--  1 vdr  1051    2 Jun 22 10:06 round-robin
-rw-------  2 vdr  1051    0 Jun 22 10:06 round-robin.lock
-rw-------  2 vdr  1051    0 Jun 22 10:06 round-robin.lock.mFTX14846
drwx------  2 vdr  root 4096 Jun 22 10:08 running

But if I start another session from the same client (a Mac OS X client),
and try to connect to frontier again, even though the first session is
still running, it says "Trying to resume session" and actually kills the
first session and then fails in resuming too.

That is a major issue. Any ideas?

Thanks,
Prakash

>>> mallah at tradeindia.com 06/21/07 4:02 PM >>>

> Hi Mallah,
>
> Could you please explain a little bit more about the shared session
> storage and how you have it setup? I saw a document saying either we
can
> setup forwarding on all the FreeNX backend servers to forward all the
> requests to the frontend load-balance server or setup shared sessions.
I
> tried doing "forwarding" from the slave servers to the frontend
server,
> but did not see any difference.
>   
My personal experience was that the documentation of setting
up load balancing is not up to the mark for someone doing it
for the first time.

I do not have in depth knowledge abt the FreeNX . fortunately
nxserver of FreeNX itself is a shell script so reading it does
provide help in debugging / understanding.

nxserver use the folder /var/lib/nxserver/db for storing session
status and information. for session persistence an use should be
connected to same server where his (suspended) session exists.
for this the session storage space should be available to the
load balancer as well as the participating servers. we achieved
it here via NFS (note this is not the best way , some one used a
RDBMS for that !!). However if u do not need session persistence
forget abt this shared stuff to start with.

I find the comments in node.conf confusing , i dumped it and read
the code of nxserver instead , it was more helpful *as far as load
balancing is concerned*

i have not done round-robin , i did "load" method that required
setting up of password less communication between the load
balancer and rest of servers. it was required so that scripts
can be run on the rest of servers for probing their "fitness"
(weight) for serving the client.

overall this process is interesting and challenging
i regret that due to short of time i cannot give exact answer
of ur question at the moment all i can say is that ITS DOABLE.
and IT WORKS. all the best

regds
mallah.











> Thanks,
> Prakash
>
>   

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