rails new

The Rack app you don't have to write

Last module you hand-rolled a Rack app: a call(env) method, an array of [status, headers, body], and a router you wrote yourself with if/elsif matching on env["PATH_INFO"]. It worked, but it was maybe 30 lines of plumbing before you'd written a single line of PawWalk logic — and every new route meant more elsifs.

Rails is that same Rack app, already built, with the plumbing done for you. Routing, database access, HTML rendering, JSON rendering — all wired up, all following one convention, so you almost never write wiring code again. This module builds one small full-stack Rails app, dogpark, so you see every piece of that machine at least once before the course goes API-only for the real PawWalk backend.