Correct way to synchronise Pi-Hole acting as DHCP server?

[jpbaril]

Hi and thank you for your app.
I'm evaluating the idea of having a second DNS server for redundancy.
My Pi-Hole is also acting as the DHCP server. I read that you cannot have two DHCP servers on a same subnet.

So what is the correct way to configure Nebula-Sync in this setup of Pi-Hole also acting as the DHCP server?

Thanks

[lovelaze]

Hi @jpbaril

Are you looking at turning off dhcp completely for the second pihole?

If so, you can use selective sync and skip syncing the dhcp settings to the replica, then just turn off the dhcp server on the replica as well:

FULL_SYNC=false
SYNC_CONFIG_DHCP=false

Rest of the sync settings you may leave on or off depending on what you need

[jpbaril]

Hi @jpbaril

Are you looking at turning off dhcp completely for the second pihole?

That's the thing, I don't know.
As I said I was with the impression you could not have two DHCP servers at the same time, so I guess I would have to disable DHCP on the second Pi-hole server, right? In that case then thanks for the suggested settings, I'll try these.

Yet, while I'm at it, so related to the fact I asked the question in the first place, and even though I understand it is somewhat a bit beyond the scope of your responsibilities, I would say that I think it could be good for the adoption of your app if you provided in the documentation a few config exemples of the typical use cases people could have that indeed made people have to use your app. For example the one I'm asking about today.

Thanks again

[manoloxxl]

For sure can run several DHCP Server in the same subnet. But they should not have the same dhcp range.

So you can configure pi-hole master by using 192.168.1.50 to 192.168.1.100 and the backup pi can use .101 up to 150

The trick is to set a delay in the config for backup pi to answer some seconds later (I use 2s) so the master pi is always the first who is answering for request. In case of failure (master offline, backup online) the dhcp will answer a bit slower than regular.

But, I don’t know if nebula does sync the static dhcp settings list without sync the other dhcp settings. You don’t want to sync the settings because then it will duplicate the dhcp ranges. But you want to sync the static list because you may want them global in your network.

Maybe it’s also possible to use keepalived to remove the delay config in case of switch to backup pi and set it back when master is online again. It’s just a line in config file.

[lovelaze]

But, I don’t know if nebula does sync the static dhcp settings list without sync the other dhcp settings. You don’t want to sync the settings because then it will duplicate the dhcp ranges. But you want to sync the static list because you may want them global in your network.

With the include/exclude config filters, nebula sync can sync any dhcp config that pihole supports.

[auyer]

Interesting take!
Mind sharing your configs ? :)

[jpbaril]

In my case, as I was fine with DHCP temporarily not being able to lease new IPs in case of my main server being down, I simply made a full unidirectional sync, but used the new exclude configs: SYNC_CONFIG_DHCP_EXCLUDE=active,start so that the second server does not activate DHCP.

In manoloxxl way of doing, I understand the static lease would need to be synchronized in both directions, which I did not want to bother doing since I wanted to keep things simple.

Yet, in the end, my more-simple setup still required a more-complex thing to really work: On the second Pi-Hole I had to create a cronjob to synchronise its static dhcp lease list with its list of local DNS. That's because DNSMasq will not take into account the DHCP leases if DHCP is not activated.

# Every hour
0 * * * * cat /etc/pihole/dhcp.leases | awk '{if ($4 != "*") print $3 " " $4}' | sort -t . -k 3,3n -k 4,4n > /etc/pihole/hosts/dhcp-leases.list