deb ddns package has different socket path than CA
I've installed packages from cloudsmith.io:
dpkg -l 'isc-kea*'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-========================-=============================-============-================================================
ii isc-kea-admin 1.7.10-isc0030920200728082656 amd64 Administration utilities for ISC Kea DHCP server
ii isc-kea-common 1.7.10-isc0030920200728082656 amd64 Common libraries for the ISC Kea DHCP server
ii isc-kea-ctrl-agent 1.7.10-isc0030920200728082656 amd64 ISC Kea DHCP server REST API service
ii isc-kea-dhcp-ddns-server 1.7.10-isc0030920200728082656 amd64 ISC Kea DHCP Dynamic DNS service
ii isc-kea-dhcp4-server 1.7.10-isc0030920200728082656 amd64 ISC Kea IPv4 DHCP server
isc-kea-ctrl-agent package has /tmp/kea-ddns-ctrl-socket in /etc/kea/kea-ctrl-agent.conf, but isc-kea-dhcp-ddns-server package has /tmp/ddns-ctrl-socket in /etc/kea/kea-dhcp-ddns.conf. Those two must match for the solution to work out of the box.