This shouldn’t have been this difficult, but it has because while there are many cool tutorials are out there, they are mostly outdated, and for some reason, the instruction on Heroku was not accessible.
While I picked acts_as_ferret because Heroku supports it, many seemed to prefer Thinking Sphinx. So, if you are not constrained (like me with Heroku), you should try that out too.
1. Install acts_as_ferret
While the instruction asks you to put version name, since Heroku only has version 0.4.3 installed, specifying a version will break it.