SUMMARY: Load Balancing PC-Admin Server

From: Peter Marelas (
Date: Sat Mar 08 1997 - 00:08:55 CST

I originally posted:

On Mon, 3 Mar 1997, Peter Marelas wrote:
> We are in the process of installing a PC-Admin server on 2 hosts,
> the NIS+ master and NIS+ replica.
> The purpose of this configuration is to provide:
> 1. Load Balancing
> 2. Redundancy
> We will be dividing the clients evenly across both servers, so depending
> on the subnet the client belongs too, one of the two PC-Admin servers
> will be the preferred, while the other being the secondary.
> What I am concerned about is the Plum license manager. Is it possible to
> keep 2 copies of all the licenses on both hosts?
> Do the Plum license servers keep each other up to date, as to what
> licenses have been used? If so, how..
> If not, does it matter if 2 clients are using the same license?

This is what I found:

Unfortunately I received 1 reply which mentioned PC-Admin should be scrapped,
and NT should be used.

Regardless, I went ahead with it and we were successful.

Heres what the configuration looks like:

        SS20 - serverA SS20 - serverB
        * Nis+ Master * NIS+ Replica
        * pcnfsd server * pcnfsd server
        * plum license server * plum license server
        * solarnetd server * solarnetd server
        * S: NFS server * S: NFS server
        * DHCP server * DHCP server

        E3000 - serverC E3000 - serverC-r
        * pcnfsd server * pcnfsd server
        * Other Apps * Other Apps

NIS+ was used for the dhcptab and subnet maps.

The dhcptab properties for serverA and serverB were modified like so:

        serverA - SNadmfw="serverA serverB"
                - Pcnfsd="serverC"
                - SNCserv="serverA serverB"
                - Licserv="serverA serverB"

        serverB - SNadmfw="serverB serverA"
                - Pcnfsd="serverC"
                - SNCserv="serverB serverA"
                - Licserv="serverB serverA"

Basically for all the services except pcnfsd, a fallback server exists.

Then we modified the client definitions in the subnet maps, so the DHCP
server and property would be halved between serverA and serverB.

If a clients primary PC-Admin server is available, it would bind to it,
except for the pcnfsd service which is on serverC (More about this later.)
If the primary PC-Admin server was not available, then on boot the PC
will continue to poll its primary PC-Admin server (which is down) and then
use the secondary after a timeout. The time a PC will take too boot if its
primary PC-Admin server is down, is about 1 minute after DHCP negotiation

The pcnfsd service is on a third system that in a High Availability Pair. The
reason for this is because we could not get the PC-Admin clients to modify
the Authentication Server used. For some reason, the PC-Admin login screen
would always use the first defined PCnfsd server for user authentication, even
if it was down.
Therefore we opted to put this service on a Highly Available server which
was already established.

Another problem is the DHCP server. If a PC's primary DHCP server is "serverA"
and serverA happens to be down. Then on boot the PC will negotiate with
serverB for an IP. But the request will fail, because it seems the in.dhcpd
process which queries the NIS+ namespace, explicitly queries the Master. Since
serverA is the master, serverB fails to update NIS+ maps when the DHCP request
is received. Not all is lost tho, because the PC-Admin client will then
fallback to using its previous "DHCP" configuration that is stored in files
on its local hard disk. I imagine this can cause problems when an
environment consists of temporary leases rather than permanent leases
like ours.

You might also be wondering why pcnfs servers are running on serverA and
serverB, when serverC is used for pcnfsd. The reason for this is because
the PC Client/User Admin tools will authenticate the administrators (pcadm)
login using pcnfsd on the "PC-Admin" server specified in the dialog box.

The last comment I'ld like to make is we did not have problems with the
License Manager. We used the same license database on both License Servers.
We did not split the database in half. The License Servers do not communicate
at all, regarding what licenses are in use etc..

Apart from the 2 gotchas (pcnfsd, dhcp), it works.

Peter Marelas

The Fulcrum Consulting Group               Peter Marelas - Consultant
12/10-16 Queen St, Melbourne VIC 3000,Australia   Ph: +61-3-9621-2100
PGP Key -> finger  Fx: +61-3-9621-2724

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