noitu/docs/deployment.md

# Deployment

The whole game is one binary. It serves the WebSocket API, the built frontend,
and its own health, readiness and version endpoints, and it reads a single
database file at startup. The supported shape is the container image behind a
reverse proxy that terminates TLS.

## Configuration

Every setting is an environment variable and every one has a working default,
so the image runs with nothing set.

| Variable | Default | Meaning |
|---|---|---|
| `NOITU_ADDR` | `:8080` | Listen address |
| `NOITU_DB_PATH` | `data/noitu.db` | Derived dictionary, opened read-only at startup |
| `NOITU_TURN_LIMIT` | `30s` | Turn deadline, identical for bot and online games |
| `NOITU_GRACE` | `30s` | How long a disconnected player's seat is held for a reconnect |
| `NOITU_ALLOWED_ORIGINS` | *(unset)* | Comma-separated origin allowlist. Unset means same-origin only |
| `NOITU_WEB_DIR` | *(unset)* | Built frontend to serve. Unset serves the API alone |
| `NOITU_TRUSTED_PROXIES` | *(unset)* | Comma-separated proxy addresses or CIDRs whose `X-Forwarded-For` is believed. Unset keys limiters on the socket peer |
| `NOITU_MAX_ROOMS` | `1000` | Ceiling on live rooms across the process; a creator past it is told `server_full` |
| `NOITU_MAX_CONNECTIONS` | `2000` | Ceiling on open WebSockets; the next upgrade gets HTTP 503 |
| `NOITU_DEBUG_ADDR` | *(unset)* | Separate listen address for `GET /debug/vars` (expvar counters). Unset means the counters exist in the process but nothing serves them |
| `NOITU_DRAIN_TIMEOUT` | `0s` | How long a shutdown waits for live games to finish before ending them anyway; see "Draining on deploy" below |

An invalid duration or count is logged and ignored rather than silently
changing the rules of the game.

One timing is not configurable: an online room closes after 10 minutes in its
lobby with no game started. It is a fixed constant because nothing about a
deployment should change how long two people have to agree on a game, and a
running game is bounded by the turn clock rather than by this. Chatting
deliberately does not reset that window — talking is not playing, or a room
could be held open for the life of the process by one message every nine
minutes.

Chat's own bounds are fixed constants for the same reason: a room keeps its
last 20 messages and one message is capped at 200 runes
(`server/internal/wsapi/room.go`).

The image sets `NOITU_ADDR`, `NOITU_DB_PATH` and `NOITU_WEB_DIR` for you.

### Origins

Leave `NOITU_ALLOWED_ORIGINS` unset when the binary serves the frontend, which
is the normal case: the page and the socket share an origin and the browser's
own check is enough. Set it only when the frontend is served from somewhere
else, and then list exactly those origins. An allowlist that is wrong in the
permissive direction lets any page open a socket as one of your players.

## The image

```sh
docker build --build-arg VERSION="$(git describe --tags --always --dirty)" -t noitu:latest .
docker run -p 8080:8080 noitu:latest
```

`make image` runs the same build with `VERSION` filled in for you; see
"Version" below.

The build downloads the ~62 MB upstream Wiktionary export in a builder stage and
derives the ~2 MB database the game uses. Only the derived file is copied into
the final image, so the upstream export never ships. The result is a
distroless image of about 25 MB running as a non-root user.

Passing `--build-arg FIXTURE_DICT=1` builds the same image against the
checked-in word sample instead. It produces a playable but tiny dictionary and
exists so the image can be tested without the download; do not ship it.

### Version

`GET /version` answers with the build's version, and the same string opens
the startup log line — the fastest way to confirm a deploy actually replaced
the running process rather than restarted the old one. It comes from
`-X main.version=...` at link time, populated from `git describe --tags
--always --dirty`. `make server` runs that command directly; the Dockerfile
cannot — `.dockerignore` deliberately keeps `.git` out of the build context,
so a stale copy never ships in the image — so it takes the version as the
`VERSION` build-arg instead, which `make image` supplies. Building the image
directly with `docker build .` and no `--build-arg VERSION=...` reports
`dev`, which is an honest answer for an unstamped build rather than a wrong
one.

### What travels with the data

The derived wordlist is CC BY-SA 4.0 while the code is Apache-2.0, so the image
carries `data/LICENSE`, `data/ATTRIBUTION.md` and `NOTICE` alongside it. CI
asserts all three are present, and that the upstream file is not. Removing them
would put the image out of compliance.

## Behind a reverse proxy

The socket is a normal HTTP upgrade, but three settings are easy to get wrong
and each one breaks the game in a way that looks like something else.

**Forward the upgrade.** Without `Upgrade` and `Connection` the handshake
returns 400 or 502 and the page sits on "Đang kết nối…" forever.

**Set a read timeout longer than the keepalive.** The server pings every 20
seconds. A proxy that closes idle connections sooner will cut players off mid
game, and it will look like a client bug because the server logs a clean close.

**Turn response buffering off.** A proxy that buffers will hold frames until it
has enough to flush, which turns a 30-second turn into a guess.

nginx:

```nginx
location /ws {
    proxy_pass http://127.0.0.1:8080;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    proxy_read_timeout 120s;
    proxy_send_timeout 120s;
    proxy_buffering off;
}

location / {
    proxy_pass http://127.0.0.1:8080;
    proxy_set_header Host $host;
}
```

Caddy needs none of this: it forwards upgrades and streams by default.

```caddy
noitu.example {
    reverse_proxy 127.0.0.1:8080
}
```

### The client's own address

Rate limiting keys on the client's address, and by default that is the
socket's own peer, `RemoteAddr`. `X-Forwarded-For` is attacker-controlled
unless the proxy is known to append to it, so it is ignored until told
otherwise. Behind a proxy every player therefore shares one bucket, which
means one client brute-forcing room codes spends everybody's join budget.

The fix is to name the proxy. Set `NOITU_TRUSTED_PROXIES` to the address, or
CIDR range, the proxy connects from — `127.0.0.1` for the nginx and Caddy
examples above, or the container network's range under Compose — and the
server walks `X-Forwarded-For` from the right, taking the first hop that is
not itself a trusted proxy. Entries a client forged sit to the left of the one
the proxy appended, so they are never reached. A peer that is not on the list
is still keyed on its socket address, header or not.

Both proxies above append the real client to `X-Forwarded-For` by default.
Do not list a range the public can connect from; that is the same as trusting
the header unconditionally.

### Capacity

Two ceilings bound the process as a whole, on top of the per-connection rate
limits: `NOITU_MAX_ROOMS` live rooms and `NOITU_MAX_CONNECTIONS` open
sockets. Past the first, creating a room answers `server_full` and the player
is asked to wait; past the second, the upgrade itself is refused with HTTP 503
so the proxy can count it. Each connection also has a frame-rate ceiling, and a
client past it is disconnected rather than throttled. The defaults are
generous for one binary on a small host; lower them if memory is tight,
because a room is a goroutine and an engine held for up to its idle window.

## Observability

Set `NOITU_DEBUG_ADDR` to a second listen address — one that is not the one
players reach — to expose `GET /debug/vars` there: standard-library
[`expvar`](https://pkg.go.dev/expvar), zero extra dependencies, a JSON object
of process counters refreshed on every write. It is never mounted on the
public address, unset or not, so leaving `NOITU_DEBUG_ADDR` unset is the same
as not having it. The counters, all prefixed `noitu_`: connections open and
total; rooms live and total, each split `bot`/`pvp`; games started and
finished the same way; words submitted, accepted, and rejected by reason;
eliminations by reason; chat lines; join attempts refused, by whether it was
the rate limit, an unknown code, or a full room; bot moves by difficulty; and
resumes attempted versus succeeded. None of it is read by the game itself —
it is a second write next to a decision already made, not an input to one.

Every rejected word also gets one structured log line at `Info`,
`word_rejected`, carrying `reason`, `word`, `link` (the syllable it had to
start with), `mode` (`bot`/`pvp`) and `room`. `word` is never the raw text a
player typed — it is normalized the same way the engine matches it (NFC,
lowercase, single-spaced) and capped at 64 runes — so the line is safe to
collect and is exactly the corpus-review question this project has open:
which words players type that the dictionary does not have. Nothing else a
player types is logged: not chat, not a nickname, not an accepted word.

## Health and readiness

`GET /healthz` returns 200 once the dictionary has loaded, for the rest of the
process's life. It does not report on live games, so it is a liveness check
rather than a readiness one, and it never moves — a proxy or orchestrator
using it to decide whether to kill the process must not see it fail during a
drain, because the process is still correctly finishing the games it has.

```sh
curl -fsS https://noitu.example/healthz
```

`GET /readyz` is the readiness check: 200 while the server is accepting new
rooms, 503 once it has started draining (see below). Point a load balancer's
"stop sending me new traffic" check here and its "restart me" check at
`/healthz`; pointing both at the same endpoint defeats the reason there are
two.

A post-deploy check worth having beyond either is a real socket open, because
both health checks pass whether or not the proxy forwards upgrades. Opening
the site and starting a game against the bot is the shortest version of that.

## Draining on deploy

Rooms are in memory, so a restart has always ended every live game — but a
plain `kill` used to do that the instant the signal arrived, which is why
"deploy when the game is quiet" was the only advice this document had.
`SIGTERM` now runs a short sequence first:

1. The server stops accepting new rooms. A creator past this point is told
   `server_restarting` — the same UI key a live shutdown sends everyone else —
   rather than `server_full`, because unlike a full room this one is never
   coming back.
2. `GET /readyz` flips to 503, so a load balancer that checks it stops routing
   new players here.
3. The server waits up to `NOITU_DRAIN_TIMEOUT` for every room with a game
   *actually running* to finish on its own turn clock. A room sitting in its
   lobby does not count — it has no game a restart would cost, and waiting for
   one would make every deploy sit out somebody's abandoned tab.
4. Once every game has finished, or the timeout passes, every player still
   connected is told the server is restarting and the process shuts down as
   it always did.

Each step logs the room and live-game count, so "did the deploy actually
wait, and for what" is answered from the log rather than guessed at.

The default, `NOITU_DRAIN_TIMEOUT=0s`, is today's behaviour: nothing waits,
every live game ends immediately. Setting it to something like `60s` turns
"deploy when the game is quiet" into "deploy whenever, and the games in
flight get up to a minute to finish before they are cut off anyway" — the
turn clock already bounds how long any one game can take, so a timeout a
little over `NOITU_TURN_LIMIT` covers the common case of a handful of games
mid-turn.

## What a restart costs

A restart with `NOITU_DRAIN_TIMEOUT` unset, or a signal harder than `SIGTERM`,
ends every live game immediately and tells players the server is restarting
rather than leaving them waiting. There is no session persistence, by design,
in this version — a game that does not finish inside the drain window is
simply lost.

## Updating the dictionary

The dictionary is a build artifact, not runtime state, and the upstream dump
is fetched fresh rather than pinned: rebuilding the image picks up whatever
`dumps.wikimedia.org` currently serves under `viwiktionary/latest/`, which is
regenerated monthly, and the database's `meta` table records the SHA-256 of
the file it was built from. To update the dictionary, rebuild and redeploy.
To change the source itself, update `DICT_URL` in the `Dockerfile`, the
`Makefile` and the builder's constant (a test asserts the three agree), then
record what changed in `data/ATTRIBUTION.md`.

Nothing migrates, because nothing persists.