The DHCP server on the UniFi Security Gateway is pretty limited; it
cannot manage static leases (reservations), and does not offer any way
to build dynamic values for e.g. hostname or boot filename. Rather than
give up these features, I decided to just move the DHCP server to one of
the Raspberry Pis; the DNS server made the most sense.
To facilitate this move, I created the *pyrocufflink-dhcp* host group,
and moved the DHCP configuration variables there. Thus, it was a simple
matter of adding *dns1.pyrocufflink.blue* to this group to relocate the
service.
Of course, to serve clients on the other subnets, the gateway needs to
have DHCP relay enabled and pointing to the new server.