I want to automate log files using ansible automation.
How can I scan log files & take action on them ?

You first need to write to a file, scan the file, take an action and shove it up your butt.

Commonly log files are send to a central log server, which would then do the analysis for you.
On the log server, the blogs will be parsed and commonly analyzed.

A common product for doing so is ELK (ElasticSearch, Logstash, Kibana). While not trivial to use, it has some advantages.

If your use case is "brute force protection": ELK is an overkill, setup fail2ban.