General questions about failover, config changes and restarting

Glenn Satchell glenn.satchell at uniq.com.au
Wed Mar 2 15:34:25 UTC 2016


Hi James

The configurations for the subnets and everything except the failover (and
possibly the keys) should be exactly the same, so editting one and scp the
file to the other server is exactly the right thing to do.

It doesn't matter too much which server is restarted first, but you should
not restart the second until the first has finished synchronising lease
information. This may take a little while if there are many thousands of
leases - I see you have a /22 and /16, so maybe up to 17000 or so leases.
Could take a few minuted depending on network speed and latency between
the servers.

Once the first server has finished synchronising, then it's ok to restart
the other server, and this should synchronise much quicker.

regards,
-glenn

On Wed, March 2, 2016 11:36 pm, James Dore wrote:
> Hi all,
>
> I’ve had a pair of DHCP servers running in a load balance/failover
> cluster for about 9 months, but haven’t really got my head round what
> happens when I make a change to the configuration.
>
> I have a bunch of config files called from the main config file thus:
>
> ##########################
> #                        #
> # Failover configuration #
> #                        #
> ##########################
> failover peer "newc-dhcp" {
>     primary;
>     address 129.67.111.199; # address of this server
>     port 519;
>     peer address 129.67.111.243; # address of the secondary dhcpd
>     peer port 519;
>    max-response-delay 60;
>    max-unacked-updates 10;
>    mclt 600;
>    split 128;
>    load balance max seconds 3;
> }
>
> key primaryhost {
>     algorithm hmac-md5;
>     secret <ssshhh!>
> };
>
> omapi-key primaryhost;
> omapi-port 7911;
>
>
> ###########################
> #                         #
> # Load the golbal options #
> #                         #
> ###########################
>
> include "/etc/dhcpd.d/master.conf"; # (Rarely!) Edit this file to set
> global options
>
> ########################
> #                      #
> # Subnet config files  #
> #                      #
> ########################
>
> include "/etc/dhcpd.d/vlan1.conf"; # 129.67.108.0/22 Main subnet and
> static assignments
> include "/etc/dhcpd.d/vlan3.conf"; # 10.30.0.0/22 Devices subnet config
> and static assignments
> include "/etc/dhcpd.d/vlan4.conf"; # 10.4.0.0/16 NAT Vlan4 Subnet config
> and static assignments
> include "/etc/dhcpd.d/annexe.conf"; # 163.1.173.0/24 Annexe subnet config
> and static assignments
>
> Both peers have pretty similar config files, the only difference being the
> secret and the address/peer address settings. Everything else is the same.
> (Should it be?)
>
> The things I’m curious about are what happens when I make a change to
> one of the Subnet config files, for instance to add a new static
> assignment. My usual method has been to edit the file one peer, and then
> scp it over to the other peer. After that, it seems like I need to do a
> number of restarts of each peer before they both return to Normal status.
> They seem to get stuck in Partner-down, Recover, or Recover Wait status
> for a while.
>
> If I can get them both in Recover Wait, then they will synchronise, but it
> seems to be difficult to get them there.
>
> Is there anything I can do to smooth the process?
>
> I can’t find much info about troubleshooting failover or load balancing,
> all my googling has turned up is instructions on initial setup. Does
> anyone have some useful pointers or links?
>
> Cheers,
> James
>
>
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> dhcp-users at lists.isc.org
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>
>




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