I am developing an android application and I am developing the server using Ruby on Rails. I want only admins to be able to access the application database. That is, the server home page should contain a "sign in" (for admins to sign in.. only 2-3 persons are gonna be admins) link but shouldn't contain a "sign up" link to prevent unauthorized users signing up. Basically, I don't want any random person to sign in to the admin page. How do I do this? 

Alternatively, what I can do is keep the "sign up here" link on the home page (with a line saying "admins only") and allow people to register but refuse users to sign in saying "sorry, u are not recognized as an admin"> I believe I can do this by hardcoding admin ids into my code and checking them everytime someone signs in... But this just looks lame

Or I can remove the signup link altogether (only keep a sign in link) and create admins's accounts from the terminal itself from my local machine on which server is running, thus preventing any random user from signing up. Again, this looks inconvenient.. 

This is my first time on web development and I have little knowledge about this. Please help! Thanks!!