I am using apache2 with mod_php and mpm_itk_module to run every virtualhost under its user. Now I am looking at mono (mod_mono) and I am not sure, if it is secure to run mono as only one process, whom the request is given by apache. The same I see with nginx & fastcgi mono. Are these really secure ways to run ASP.NET mono application on linux server?
Yes, it's secure to do this but all AppDomain's will be subject to the same configuration. If you need to define different quotas, isolate experimental code or use a different version of mono you will need to run multiple instances of mod-mono-server.
See the documentation for more information