How to create power failure event based web app?

I am just looking to do certain actions on power failures for instance I want to enable a Firewall Rule in my Mikrotik Router when power fails so I am wondering how would I be exactly able to do that?? I have thought about solutions..But can't get any??? Any way to make it web based so that the power failure results are added to a text file through php etc so that I can host that page on my hosting and then read that text file through my Mikrotik router and perform certain actions according to the data stored???