nginx resolves a plain `proxy_pass http://server:8080;` hostname once at
config-load time. On a cold `docker compose up` that creates every
container at once, the `server` container isn't always registered in
Docker's embedded DNS yet by the time the client's nginx starts — nginx
then fails immediately ("host not found in upstream") and doesn't retry,
so it just crash-loops.
Route the target through a variable instead (`set $upstream_server ...;
proxy_pass $upstream_server;`) with an explicit `resolver`, which makes
nginx resolve the hostname lazily per-request via Docker's DNS rather than
once at startup. Also add `depends_on: [server]` on the client service so
it at least doesn't start before the server container exists at all.
Verified with repeated `docker compose down && docker compose up` cycles
locally — this only reliably reproduced starting every container from
nothing simultaneously, which prior local testing hadn't actually done
(the server container had usually stayed running across rebuilds).
The client always called a hardcoded http://localhost:5144, which only
worked when browser and server shared the same "localhost" — breaks for
any real remote deployment, since the browser would try to reach that
port on the visitor's own machine instead of the actual server.
Now every environment routes /api/* to the server under the same origin
the page was loaded from, so the client code needs no per-environment URL:
- Docker (client container's own nginx) proxies /api/ to the server
container.
- `npm run dev` (Vite) proxies /api to localhost:5144 via server.proxy.
- Production nginx (reverse proxy + TLS) just needs to forward everything
to the client container, which already knows how to route /api itself.
Also incidentally removes CORS from the picture everywhere, since none of
these setups make a cross-origin request anymore.
Full-stack F# (Domain/Server/Client via Fable+Elmish+Feliz), PostgreSQL
persistence via Dapper, Docker Compose deployment. Student quiz-taking flow
with time-limit enforcement and focus-loss tracking, Teacher question bank
and quiz builder with results analytics, Admin user management.
