Do I have to host something myself for halion clock:it go?

No. We operate the complete backend for the mobile application for halion clock:it go at a German hosting partner with a data center in Frankfurt / Main. The mobile devices communicate exclusively with this backend and not directly with halion clock:it or your HR solution in your company network. And even for communication between the mobile backend and the local installation of halion clock:it or your HR solution, no ports need to be opened in your firewall for incoming communication.