Ruby on Rails 4: Where i have to put Common code?

I am new to Ruby on rails. i am using rails 4.1.6 and what i want is to make log of all the process in one text file (like index page accessed, view page access etc..). for that i want to create common function, in which i can pass my text as agrs, i had do some R&D on that and i found this : In Rails, where to put useful functions for both controllers and models, but it seems that it is not working with active admin resources. so, for active admin controller and model, i have to create any other modules (i.e. on other location let say /admin/) or anything else i have to do ?

is there any global location that we can use in active admin like component in cakephp.

thanks