[Dnsmasq-discuss] Further thoughts/questions on failover

Geoff Back geoff at demonlair.co.uk
Thu Sep 2 14:46:12 UTC 2021

On 02/09/2021 15:30, Chris Green wrote:
> On Thu, Sep 02, 2021 at 02:58:44PM +0100, Kevin Tedder wrote:
>> Chris
>> You just need to update the /etc/resolv.conf file on each of your clients to
>> point them at both DNS's.
>> e.g
>> nameserver
>> nameserver
>> The client will now ask both DNS servers. It will get a response even if one
>> of them is off-line.
> Does that work satisfactorily though?  OK, there's a secondary DNS
> server on the system but it won't have all the local systems' names in
> its cache will it?  My main reason for running a local DNS is so that
> all systems on my LAN have proper names.  These names will only be in
> the DNS instance which was their DHCP server as well won't they?

What about if each instance was set to forward queries for the local
domain to the other one?
So if each is configured with "domain=example.com", also add
"server=/example.com/<address>" where on each server the <address> is
the IP of the other one?

I haven't tried this, but I believe example.com names known to the local
server would be returned immediately and any others would be forwarded
to the other one.

>> Your solution to move the SD card to another RPI is fine, unless the issue
>> is a corrupted SD Card.  Wasn't this the original issue that you are trying
>> to avoid?
> I wasn't aiming to move the SD card, I was aiming to keep an 'as up to
> date as possible' image of the running DNS system.  Possibly, in
> addition, writing the image out to an actual, spare, SD card at
> intervals.
>> Personally, I'd rather have two systems fully operational all the time. To
>> discover that the back up solution is not working at the critical moment is
>> the same as not having a backup at all.
> Is there some way the two systems can share the client names supplied
> at DHCP time?
>> The added benefit is maintenance.  You can take one off-line to
>> update/upgrade whilst the other continues to provide service. 
> Yes, I quite agree there.


Geoff Back
What if we're all just characters in someone's nightmares?

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