Premier League Predictor: FastAPI & Redis — Chapter 12, Exercise 1
==================================================================

TASK
Mount the app at /tools/predictor/ instead, and separately try a location
whose proxy_pass has no trailing slash. Report the status codes for the
page, a script file and an API call in each case, and say what changed in
the app (nothing) versus in nginx.

SOLUTION

nginx, first case:

  location = /tools/predictor { return 301 /tools/predictor/; }
  location /tools/predictor/ {
    proxy_pass http://plapp:8000/;          # trailing slash
    proxy_set_header Host $host;
  }

  /tools/predictor/                 -> 200
  /tools/predictor/app.js           -> 200
  /tools/predictor/api/seasons      -> 200

nginx, second case (no trailing slash on proxy_pass):

  location = /nostrip { return 301 /nostrip/; }
  location /nostrip/ {
    proxy_pass http://plapp:8000;           # no trailing slash
    proxy_set_header Host $host;
  }

  /nostrip/                         -> 404
  /nostrip/api/seasons              -> 404

With a URI on proxy_pass (even just "/"), nginx replaces the matched
location prefix with it, so the app receives / and /api/seasons. With no
URI, nginx forwards the request path unchanged, so the app is asked for
/nostrip/ and /nostrip/api/seasons, which it has no routes for. (The
script file under this second prefix was not requested in the test.)

What changed: only nginx. The app was not touched between the two
mounts, and the page works at both prefixes because its asset and fetch
URLs are relative and resolve against wherever the page is served from.

WHY THIS WORKS AS AN ANSWER
----------------------------
It reports real status codes for both nginx forms, explains the 404 from
how proxy_pass treats the location prefix, and says exactly which layer
changed.