Upgraded firmware cloudkey gen 2 to 5.12.22

From version
Controller: 5.11.50 (Build: atag_5.11.50_12745)
CLOUD KEY FIRMWARE: UCKP.apq8053.v1.1.0.aa44aee.190826.2316

Upgrade to new version
Controller: 5.12.22 (Build: atag_5.12.22_12966)
CLOUD KEY FIRMWARE: UCKP.apq8053.v1.1.0.aa44aee.190826.2316

Steps:
# ssh ubnt@${IP_ADDRESS_CONTROLLER}
# cd /tmp
# wget https://dl.ui.com/unifi/5.12.22/unifi_sysvinit_all.deb
# dpkg -i unifi_sysvinit_all.deb
(Reading database ... 30572 files and directories currently installed.)
Preparing to unpack unifi_sysvinit_all.deb ...
Unpacking unifi (5.12.22-12966-1) over (5.11.50-12745-1) ...
Setting up unifi (5.12.22-12966-1) ...
Processing triggers for systemd (241-5~bpo9+1) ...
UniFi-CloudKey-Gen2-Plus:/tmp# rm -f unifi_sysvinit_all.deb
UniFi-CloudKey-Gen2-Plus:/tmp# reboot

Access again the web interface of Unifi controller and the software should be updated.

Good Resources:
1. https://community.ui.com/releases/UniFi-Network-Controller-5-12-22/263c8b60-def8-4667-85c3-87a6200a6c9b

2. https://www.ui.com/download/unifi/unifi-cloud-key-gen2/default/unifi-network-controller-51222-debianubuntu-linux-and-unifi-cloud-key

3. https://help.ubnt.com/hc/en-us/articles/360012282453-UniFi-How-to-Install-Upgrade-the-UniFi-Network-Controller-Software

4. https://www.youtube.com/watch?v=YEm8tKkVJUg