Nagios has check_log but that is not great for memory, I believe it loads the entire log file into memory to take a diff to only check on the entries missed.

There is check_logfile which has a similar name but is a different library, I wrote about how to set this up a while ago: https://medium.com/luma-consulting/how-to-install-check-logf...

It's not super obvious how this plugin works unfortunately. Not the craziest thing in the world to configure but certainly not easy starting from zero!