[Dnsmasq-discuss] Further thoughts/questions on failover

Kevin Tedder kevintedder at hotmail.com
Thu Sep 2 13:58:44 UTC 2021


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 192.168.1.2
nameserver 192.168.1.3

The client will now ask both DNS servers. It will get a response even if one
of them is off-line.


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?

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.
The added benefit is maintenance.  You can take one off-line to
update/upgrade whilst the other continues to provide service. 
 
Kevin


-----Original Message-----
From: Dnsmasq-discuss
[mailto:dnsmasq-discuss-bounces at lists.thekelleys.org.uk] On Behalf Of Chris
Green
Sent: 02 September 2021 13:45
To: dnsmasq-discuss at lists.thekelleys.org.uk
Subject: [Dnsmasq-discuss] Further thoughts/questions on failover

I'm still ruminating on this problem! :-)

A number of people are using docker containers to manage this, one
live dnsmasq in a container is the default DNS/DHCP for the system and
another dnsmasq container is maintained to keep its files in sync with
the running one.

So far so good.

What I don't follow is what happens if/when failure occurs as I don't
see how the replacement dnsmasq instance can appear at the same
address on the LAN.  So, unless all systems are rebooted they will
lose DNS won't they?

E.g. My default dnsmasq instance runs on a system at 192.168.1.2, if I
had a 'clone' docker container on my desktop machine it would be at
address 192.168.1.3.  So, if 192.168.1.2 dies and I start the dnsmasq
container on my desktop machine it's at 192.168.1.3 but all machines
on the network are configured (until reboot or DHCP reload time) to
use 192.168.1.2.

Am I missing something very obvious here (probably!).  

Just maintaining a Rasberry Pi image and updating the dnsmasq files
on it would actually work better (for me anyway) as I could copy it
out to an actual SD card regularly and all I'd need to do to recover
after a failure would be to plug the SD card into a non-dead Pi and
turn it on.

-- 
Chris Green

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