I have various heterogenous services from my company able to log things into files, but e.g. not able to send mails on their own. Additionally, I have logging into files from Apache httpd and Tomcat, Postgres, Upstart and various other sources by default not using e.g. Syslog. The commons sense of all those services is using files, but log size, formats of the messages, rotation or not etc. differ.
So what I'm looking for is some log monitor which focusses on configured files and provides triggers to match newly added content to those files against some regular expressions or such to send mails with error messages.
I would like to have something stand-alone, focussing on log file monitoring with triggers and being somewhat efficient by e.g. using file system events to get notified of changed files, only reading the end of files on changes instead of parsing the whole file and such. I need some flexibility in defining triggers, though, but besides that it only needs to send mails with log messages to some arbitrary addresses. Not even on its own, supporting a local sendmail is absolutely enough, with very little templating features for those mails. I don't even care much for things like recognizing multiple error messages or such.
I've read the whole day about that topic and found various different solutions, things like Graylog, Logstash, plugins for Nagios/Zabbix etc. But from what I've read, all of those have serious drawbacks for my environment: Graylog and Logstash seem to have a heavy setup and dependencies and provide functions I simply don't need, like searching in logs. I currently don't use Nagios and Zabbix either and am not sure how their log monitoring plugins perform, because they seem to poll log files time based and such. Additionally, Zabbix's config looks a bit hard to maintain as well.
So is there something more focussed available?