Is there a plug in for Icinga2 that can read a log or text file on a host that needs to be monitored and search for specific words which triggers a notofication? If not, is there a tutorial on how to write a Icinga plug in myself.
Kind regards
check_logfiles might be an option for you. For writing your own plugins please check development guidelines (do worry about the name Nagios, the guidelines are valid for icinga as well).
Please use our own documentation in the future, this mimics the plugin development guidelines but enriches that with more clear details and programmatic examples 
https://icinga.com/docs/icinga2/latest/doc/05-service-monitoring/#plugin-api
Cheers,
Michael