best practices for two-location DDNS for a single domain

Chuck Swiger cswiger at mac.com
Fri Jan 13 01:34:28 UTC 2012


Hi--

On Jan 12, 2012, at 5:04 PM, Chris McCraw wrote:
> But those aren't an option here - they both need to serve the same
> domain and both need to allow local DDNS updates visible from both
> sides, and work in the absence of a network between the two.  I've
> done some searching and it does not appear that BIND fully supports
> this setup natively.  Please correct me if I'm wrong!

I'm not sure that anything will fully solve your requirements as stated.

The normal implementation of a fault-tolerant system requires a single master server, and the backups simply write through changes they see back to that master.  If the master drops out, then a backup promotes itself to master, but the old master needs to no longer be accepting updates.  Trying to update two "masters" without some kind of network link available between them means you've created a split horizon [1], and they will move out of sync with each other as they get updates which the other side(s) doesn't/don't see.

> I found a potential workaround using a dual-master setup with some
> magic to manually sync the updates back and forth, but that magic
> seems like it might end up being fragile.

Yeah, "fragile" meaning it will fail if the link between them drops out and a conflicting update is received which cannot be reconciled with the other side(s).

Regards,
-- 
-Chuck

[1]: "split horizon" in the terminology of cluster failover; not "split horizon DNS" meaning views based upon (ie) request source address.




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