Challenge 3: Design an Optional Debug Service — Possible Solution
====================================================================

services:
  adminer:
    image: adminer:latest
    ports:
      - "8080:8080"
    profiles: ["debug"]

Normal startup (adminer never starts):
  docker compose up

Deliberately starting it when needed:
  docker compose --profile debug up

WHY THIS WORKS AS AN ANSWER
------------------------------
profiles: ["debug"] marks adminer as belonging ONLY to the "debug"
profile — Compose's default behavior is to skip any service tagged
with a profile unless that specific profile is explicitly activated.
This means a plain docker compose up (with no --profile flag) starts
every OTHER service normally defined without a profiles key, while
adminer is simply excluded from that run entirely — exactly the "never
starts during a normal up" requirement.

Running docker compose --profile debug up explicitly opts into the
"debug" profile, which includes both adminer (tagged with that
profile) and every other service that has no profiles key at all
(services without a profiles key always start regardless of which
profiles are active) — giving a deliberate, opt-in way to bring up the
admin UI only when it's actually needed for debugging, without it
cluttering every normal development or CI run.