dnsmichi I know, I just upgraded from 2.7 to 2.8 whit yum and read documentatin, I made db schema upgrade too, but when I restarted Icinga, it didn't started anymore, so I had to search log for a solution:
1) after upgrading, the folder /etc/icinga2/repository.d didn't exists anymore, here the log:
Nov 20 12:37:51 vm-lxmonitor icinga2: [2017-11-20 12:37:51 +0100] critical/config: Error: Error while evaluating expression: Function call 'opendir' for file '/etc/icinga2/repository.d' failed with error code 2, 'No such file or directory'
Removing 'include_recursive “repository.d”' in etc/icinga2.conf solved this issue.
2) the cert files problem, I had to manually copy cert files to the new location