I installed an icinga2 monitoring system on a Centos8 system. It was installed well. I wanted to set Icingaweb2 to https, but I get the following message:
Backend unavailable
It seems that the PHP FPM service is not running. Make sure to start PHP FPM service in order to access Icinga Web 2. If you upgraded Icinga Web 2 recently, make sure to read the docs regarding PHP FPM, also locally available under /usr/share/icingaweb2/doc/02-Installation.md.
php-fm service is installed and running. The web interface starts without encryption.
httpd configuration file (icingaweb2-ssl.conf) what settings are recommended or possibly selinux error. In principle, I set up selinux well.
Assuming that PHP FPM is installed/configured according to docs, we can move to the web server.
While creating the OP, it asked you for information reguard versions of various things like PHP, Webserver, Icinga2, Icingaweb2, etc, but none of that information is present.
Assuming you are using Apache or Nginx, you will need to make sure your config files are correct, and check the logs for whichever webserver you are using to see what is going on there.
If you suspect selinux is causing pain, you can quickly test with setenforce 0 to put SELinux in permissive mode (this does NOT disable selinux, but tells it to run, allowing things to happen as if it were disabled). If everything works there, then you will need to do some selinux troubleshooting. Here are some selinux troubleshooting tips
I searched the apache config file from the internet to use https, in the meantime I found this file to be the source of the error. In this config i am not so used to it so i used one by one, of course correcting the data about me.
I took out the next part at the end of the config file and it already works.