Failover Questions

[Glenn Satchell]

>Date: Fri, 19 Jan 2007 16:54:34 -0500
>From: Jonathan Brockmeier <brockj at hope.edu>
>To: dhcp-users at isc.org
>Subject: Failover Questions
>
>We are getting ready to move from 1 DHCP server to 2 that load balance.  
>I have been having a headache for the last couple of days on some question:
>
>1)  In the failover peer section defining the connection between 
>primary+seconday and secondary+primary should that be the same "name" on 
>both the primary and secondary servers?

Here's a working example, primary first and then secondary:

failover peer "Uniq14subnet" {
  primary;
  address drill.uniq.com.au;
  port 519;
  peer address lager.uniq.com.au;
  peer port 519;
  max-response-delay 60;
  max-unacked-updates 10;
  mclt 3600;
  split 128;
  load balance max seconds 3;
}

failover peer "Uniq14subnet" {
  secondary;
  address lager.uniq.com.au;
  port 519;
  peer address drill.uniq.com.au;
  peer port 519;
  max-response-delay 60;
  max-unacked-updates 10;
  load balance max seconds 3;
}

>2) Right now we use subclass statements to put various hardware 
>addresses into different pools.  We write them to an include file and 
>restart the server right now.  This seems like a very dangerous thing to 
>do on two different servers and maintain better overall service.  Does 
>anyone have examples of how to dynamically do this via omshell or other 
>ways to do this?

The general best practise for failover systems is to use a master
dhcpd.conf file that is the same for both hosts and include a file
containing the failover peer declarations, as this bit is unique to
each host.

So, edit the master file, then copy it to the other host. Restart the
secondary then restart the primary. This order is importantin the case
of new subnets being added. If you do it theother way the primary will
try tosendthem tothe secondary which will reject the new subnets
because they are not in its configuration.

>3) Does actions done in omshell (on primary) get propagated to the 
>secondary or they need to be done via omshell on both?

No. You need to do equivalent actions to both hosts.

regards,
-glenn