I get a lot of questions how people have to install the Unifi Controller software on a Raspberry Pi. This is not a big deal and can be easily done by a few steps. And please remember, this is how I do it, there are some other possibilites.
echo 'deb http://www.ubnt.com/downloads/unifi/debian stable ubiquiti' | sudo tee -a /etc/apt/sources.list.d/ubnt.list > /dev/null
sudo apt-get install dirmngr
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv C0A52C50
sudo apt-get update
sudo apt-get install unifi
sudo apt-get install oracle-java8-jdk
echo 'JAVA_HOME=/usr/lib/jvm/jdk-8-oracle-arm32-vfp-hflt' | sudo tee /etc/default/unifi > /dev/null
sudo systemctl disable mongodb
sudo systemctl stop mongodb
sudo reboot
This reboot can take two or three minutes until the controller is fully loaded and reachable. After a cup of coffee you can point your browser to https://localhost:8443
and start with your controller setup.