I use OpenWRT on a few devices as dumb APs. I typically have removed all settings in /etc/config/dhcp except for the 'config dnsmasq' settings, but I've noticed that every time I upgrade, OpenWRT recreates a local DHCP server.
I've read in another thread that this is expected behavior of OpenWRT, so my question is: What are the minimum settings I need to maintain so that the DHCP will stay disabled during an upgrade? Is it as simple as this?
config dhcp 'lan'
option ignore '1'
The ignore line is the key one. As long as that is in place, it will remain persistent in the configuration. With that done, you do not need to disable the dnsmasq service, nor would it be an issue if the service becomes re-enabled (if you did disable it).
Likewise, the firewall does not need to be disabled, but you should always make sure that the network (lan in your case) is associated with a zone that has input 'ACCEPT' so that you don't get locked out.
You can add
config dnsmasq
...
list interface 'loopback'
to make also DNS(cache) to listen on localhost.