AW: How to modify "A" records on the slave when master is down?

Melbinger Christian Christian.Melbinger at
Wed Dec 3 14:58:45 UTC 2008


I don't think there's a clean way to modify the zone of a slave. The only way to do this is stopping the service (or freezing the zone, if possible), modify the zonefile by hand (since it's a flat file) and start the service up again. Since all the slaves replicate only from the master, you'll have to change the entry on every machine.

Once the master is up again, you'll have to make the change there again, which end up being replicated automatically... Depending on the design of your zonefiles, this would work

The major backdraw is that modifying the slaves can, when using differential updates, (guessing) have unexpected results... So you would be advised deleting the journalling file on the master before starting the service

If not using dhcp into these zones, you could deligate one of the slaves to a new master (by changing the named.conf),  normal updates and let everyone replicate from this machine. (But check first whichi zone ist most up2date... Just to be sure)

There's also the question how you manage the entries normally. Some sort of management software? By hand? If by software you may not be able to delegate another one as master

We're planning to set up our prim. dns in failover setup, meaning the zonefiles are live mirrored to another server, which in case of failure of the real prim takes over the virtual ip and playes along. (the machines are in the same ip range, but on different locations)
The files are mirrored using DRBD, and a breakdown recognized by Linux-HA
The failover peer has a second interface on which another inscance of bind runs, beeing the secondary server. So in case of breakdown one server is primary and secondary, but thats better than no prim at all..

This setup also enables us to do any maintanace on the machines, whilst only having a few seconds downtime of the primary (you can initiate the failover by hand).

Christian Melbinger
Netzwerk & Security

WienIT EDV Dienstleistungsgesellschaft mbH & Co KG
A-1120 Wien, Hetzendorfer Stra?e 30-32
tel: +43 (1) 90405 6702
fax: +43 (1) 90405 88 6700
mailto:christian.melbinger at

-----Urspr?ngliche Nachricht-----
Von: bind-users-bounces at [mailto:bind-users-bounces at] Im Auftrag von stevehunter_1 at
Gesendet: Samstag, 22. November 2008 06:10
An: comp-protocols-dns-bind at
Betreff: How to modify "A" records on the slave when master is down?

Hello.  I have two geographically different datacenters.  Each
datacenter has two instances of BIND.

There is one master out of these four.  The zones will have multiple
"A" records (pointing to the two datacenters to provide some minimal
amount of redundancy and load balancing)

What I want to do is put together a plan for when the master either
fails or the master becomes unavailable.

So if your master fails, or more likely, it becomes unavailable, and I
need to change the "A" records on the other slaves, how do you do it?

Can I have a master in each datacenter and a slave in each datacenter,
but a change made to any master propagates to all slaves?  For that
matter, can I just have four masters and be done with it?

It doesnt make sense that I could have multiple masters.. but I have
no idea how to solve this problem.  If datacenter A goes down for
three days, i want to be able to modify the slave "A" records to stop
pointing to the bad datacenter.  And when the datacenter comes back up
and the old master is alive, I want everything to work.

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