Re: Bind Redundant master server for single zone file.

[Ian Forbes <iforbes@zsd.co.za>]

On Wednesday 22 June 2005 15:29, Ian Forbes wrote:

> Is it possible to setup two bind servers such that they can both be
> "master" for the same zone, and update each other as a master would
> update a slave when ever the zone file is modified?

After much thought and investigation (and not too much sleep) I have 
come up with three options:


OPTION 1: The "right" way.

- Install "Power DNS" with a Postgres backend on each server
- Install "PostgreSQL Replicator" (http://pgreplicator.sourceforge.net/) 
on each server
- Set a time stamp based contention resolution rule
- Modify Dhis to update the local database on each server

( MySQL's native replication won't work in this application, as it is 
one way master-slave only.)


OPTION 2: The "kludge" way. (It should work - particularly as the 
servers will not go down very often - but it won't scale)

- Set up two "master" servers using bind.
- Modify Dhis to run "nsupdate" to update both servers each time an IP 
is updated. It can be set to use tcp instead of udp for reliability.
- Monitor the return codes from nsupdate, and set a "dirty" flag if the 
update fails. This normally means the other server, or the network is 
down or the other server has crashed.
- Run a period script which checks for the presence of a "dirty" flag, 
that the other server is and that it is ping-able. 
- When all of these test are true, restart the Dhis server. 
- This will force all clients to log in again and resubmit their latest 
IP's, which in turn will be propergated onto both servers. (This is not 
as expensive as it seems as each client runs a "ping" process every 
minute anyhow.)


OPTION 3 <grin>: 

- Install a M$ server at each location sharing an Active Directory.
- Install DNS on each server with zone in the AD. 
- Have Dhis nsupdate the DNS running on each local server
- Rely on AD to replicate the zone. 
(For all it's shortcomings, M$ implementation of DNS is supposed to be 
able to do this!).

If anybody has first hand experience with this type of application, 
please let me have your comments. This looks like more work than I 
first expected. I think I will give the last one option a miss.

Thanks


Ian