# gpu-turnstile

GPU arbitration proxy for Ollama + ComfyUI. One consumer GPU is shared by an
LLM server (Ollama) and an image generator (ComfyUI); gpu-turnstile sits in
front of both and guarantees the GPU is always in exactly one of three states:
`idle`, `llm` (N ≥ 1 Ollama requests in flight), or `image` (exactly one
ComfyUI job, Ollama models unloaded). See [SPEC.md](SPEC.md) for the full
design.

gpu-turnstile listens on the ports the services normally use; the actual
services run one port higher (Ollama on 11435, ComfyUI on 8189).

```
LiteLLM / Open WebUI ──► :11434 ─┐                           ┌─► Ollama  :11435
                                 ├── gpu-turnstile (1 lock) ──┤
Open WebUI / n8n ────► :8188  ───┘                           └─► ComfyUI :8189
```

- LLM endpoints (`/api/generate`, `/api/chat`, `/api/embed`, `/v1/*`) take the
  LLM lock: concurrent requests allowed, but blocked while an image job is
  active or waiting (image priority). Blocked requests either hang until the
  lock is free (`LLM_BUSY_MODE=wait`, default) or fail immediately with 503
  (or 429) + `Retry-After` (`LLM_BUSY_MODE=reject`) — the latter lets routers
  like LiteLLM cool down and retry instead of holding a hung connection.
- `POST /prompt` on the ComfyUI listener takes the image lock: new LLM
  requests block, in-flight LLMs drain, Ollama models are unloaded, the prompt
  is forwarded, and the lock is held until the job finishes and ComfyUI frees
  its VRAM.
- Everything else (including websockets and all streaming) passes through
  transparently and unbuffered.

Each consumer is enabled by setting its URL (`OLLAMA_URL`, `COMFY_URL`) and
disabled by leaving it empty — at least one is required. With only Ollama
the proxy is a pass-through (no image jobs can arrive); with only ComfyUI
the Ollama unload/warm steps are skipped. Future consumers (e.g. local game
detection) plug into the same lock the same way.

## Configuration

Configuration comes from environment variables and/or an `.env`-style
config file (`KEY=VALUE` lines, `#` comments). File lookup order:
`-config <path>` flag, then `GPU_TURNSTILE_CONFIG`, then
`gpu-turnstile.env` next to the executable. Process environment variables
override file values. Invalid values fail at startup.

| Var | Default | Meaning |
|---|---|---|
| `LISTEN_OLLAMA` | `:11434` | Listener for Ollama-compatible clients |
| `LISTEN_COMFY` | `:8188` | Listener for ComfyUI clients |
| `OLLAMA_URL` | _(empty = disabled)_ | Ollama upstream; set to enable the Ollama consumer |
| `COMFY_URL` | _(empty = disabled)_ | ComfyUI upstream; set to enable the ComfyUI consumer |
| `UNLOAD_TIMEOUT` | `60s` | Wait for Ollama to unload before an image job |
| `JOB_TIMEOUT` | `15m` | Wait for a ComfyUI job to finish |
| `LLM_WAIT_TIMEOUT` | `10m` | Max lock wait for an LLM request before 503 (wait mode) |
| `LLM_BUSY_MODE` | `wait` | `wait` = hold blocked LLM requests; `reject` = fail them immediately |
| `LLM_BUSY_STATUS` | `503` | HTTP status for rejected LLM requests in reject mode (400–599, e.g. 429) |
| `BUSY_RETRY_AFTER` | `30` | Seconds sent as `Retry-After` on busy responses (both modes) |
| `WARM_MODEL` | _(empty)_ | Model to reload after an image job (off by default) |
| `COMFY_CMD` | _(empty = unmanaged)_ | Supervise ComfyUI: start on demand, stop when idle to free VRAM. Requires `COMFY_URL` |
| `COMFY_DIR` | _(empty)_ | Working directory for `COMFY_CMD` |
| `COMFY_IDLE_TIMEOUT` | `5m` | Stop the managed ComfyUI after this long idle |
| `COMFY_START_TIMEOUT` | `2m` | Max wait for the managed ComfyUI to come up |
| `LOGLEVEL` | `warn` | `info` logs every request (colored arrows in text mode), `debug` adds lock transitions. `LOG_LEVEL` works as an alias |
| `LOG_FORMAT` | `text` | `json` for structured JSON logs |
| `LOG_FILE` | _(empty)_ | Append logs to this file instead of stderr |
| `UNLOAD_POLL_INTERVAL` | `500ms` | `/api/ps` poll interval while unloading |
| `HISTORY_POLL_INTERVAL` | `1s` | `/history/<id>` poll interval while a job runs |
| `PROBE_TIMEOUT` | `5s` | Startup probe of both upstreams (also per-probe health check timeout) |
| `HEALTH_INTERVAL` | `30s` | Periodic upstream probe; down/recovered changes are logged |
| `FREE_TIMEOUT` | `30s` | `POST /free` call after an image job |
| `WARM_TIMEOUT` | `2m` | Warm-model reload after an image job |
| `SHUTDOWN_TIMEOUT` | `10s` | Graceful shutdown on SIGINT/SIGTERM |
| `BACKOFF_INITIAL` | `1s` | First retry wait when an upstream refuses a connection |
| `BACKOFF_MAX` | `60s` | Cap for the exponential retry backoff |
| `PROMPT_CAPTURE_LIMIT` | `65536` | Bytes of the `/prompt` response buffered to find `prompt_id` (pass-through is unaffected) |
| `AUTO_UPDATE` | `true` | Poll the Gitea releases API for signed updates |
| `UPDATE_INTERVAL` | `6h` | Auto-update check interval |
| `UPDATE_REPO` | `https://git.rambossek.at/PUBLIC/gpu-turnstile` | Repository checked for releases |
| `UPDATE_ASSET` | `gpu-turnstile.exe` | Release asset to download |
| `APP_VER` | `stable` | `dev` disables updates, `stable` tracks latest, or pin an exact `vX.Y.Z` |

## Observability

- `GET /healthz` (both listeners): `{"state":"idle|llm|image","llm_inflight":N,"image_pending":B}`
- `GET /metrics` (both listeners): Prometheus text format — `gpu_turnstile_state`,
  `gpu_turnstile_llm_inflight`, `gpu_turnstile_image_pending`,
  `gpu_turnstile_image_jobs_total`, `gpu_turnstile_lock_wait_seconds`
  (histogram, `kind="llm|image"`), `gpu_turnstile_unload_seconds`.
- Logs: startup logs the version and every setting (visible even at the
  default `warn` level). With `LOGLEVEL=info` or `debug`, every request
  logs a `-->` incoming line and a `<--` response line with status and
  duration — ANSI-colored (cyan incoming; green/yellow/red by status
  class) in text mode, which renders in `docker compose logs` on Windows
  Terminal. Set `NO_COLOR` to disable colors.

## Managed ComfyUI (`COMFY_CMD`)

Don't want ComfyUI running 24/7 (it holds VRAM even when idle — and the
Desktop app kills its server when you close it)? Point `COMFY_CMD` at a
standalone launch command and gpu-turnstile supervises it: the first
request starts it, it stops again after `COMFY_IDLE_TIMEOUT` (default 5m)
without work, freeing the GPU for games or the LLM. Example for a Desktop
install (run it once manually to confirm it works):

```
COMFY_URL=http://127.0.0.1:8188
COMFY_CMD="C:\ComfyUI\.venv\Scripts\python.exe ComfyUI\main.py --port 8188"
COMFY_DIR=C:\ComfyUI
```

`POST /prompt` waits for the server to answer before taking the GPU lock
(LLM traffic keeps flowing while torch loads); crashes are logged and the
next request respawns. Shutting gpu-turnstile down stops the child too.

Running the ComfyUI Desktop app alongside is safe: if something already
answers on the port, gpu-turnstile just uses it instead of spawning
(and never kills it — it only ever stops its own child). If the managed
instance already holds the port when you open the desktop app, the
desktop's server is the one that fails to bind.

## Build and run

```sh
go build ./cmd/gpu-turnstile
OLLAMA_URL=http://127.0.0.1:11435 COMFY_URL=http://127.0.0.1:8189 ./gpu-turnstile
```

Running the binary with no arguments in a terminal prints the help screen
(same as `-h`/`--help`); without a terminal (services, containers) a bare
invocation starts the proxy.

### Run natively on Windows (current primary deployment)

Download `gpu-turnstile.exe` from a release and install it as a Windows
service — no admin shell needed, a UAC prompt appears automatically and
the elevated child does the work (its window waits for Enter so you can
read the result):

```sh
gpu-turnstile.exe --install-service        # installs into Program Files, auto-start
gpu-turnstile.exe --install-service --no-copy   # register in place instead
gpu-turnstile.exe --remove-service
```

Layout: `C:\Program Files\gpu-turnstile\` holds the exe and
`gpu-turnstile.env`, logs go to `C:\ProgramData\gpu-turnstile\`. If you
install without a config, the installer writes a sample env file with every
setting commented and explained — only `LOG_FILE` is active (a service has
no console). Your own `LOG_FILE` setting is always kept. The service always
runs
as the virtual account `NT SERVICE\gpu-turnstile` (low-privilege,
per-service, no password); the installer automatically grants it write
access to the install and data directories — nothing else to do.

Re-running `--install-service` is safe: it stops a running service,
replaces the installed binary only if it changed, fixes the registration
only where it drifted, and restarts the service only if it was running.

### Run natively on Linux (systemd)

The same binary works on Linux. Install it as a systemd service as root:

```sh
gpu-turnstile --install-service            # installs into /var/lib/gpu-turnstile, enables + starts
gpu-turnstile --install-service --no-copy  # register in place instead
gpu-turnstile --remove-service
```

The unit (`/etc/systemd/system/gpu-turnstile.service`) is `Type=notify`:
`systemctl start` blocks until the listeners are actually bound, a 30 s
watchdog restarts the process if it wedges, and logs land in the journal
(`journalctl -u gpu-turnstile -f`) unless `LOG_FILE` is set. Install
copies the binary to `/var/lib/gpu-turnstile/` and the config to
`/etc/gpu-turnstile.env` (edit that one after installing). The service
runs sandboxed with `DynamicUser=yes` — a transient low-privilege UID,
read-only filesystem except its install dir (so self-update keeps
working), no capabilities, syscall-filtered: same least-privilege idea as
the Windows virtual account. The notify integration is a no-op in
containers and interactive shells.

**Auto-update is on by default**: the binary checks the repo's latest
release on startup and every `UPDATE_INTERVAL`, verifies the Ed25519
signature of the download against the public key embedded at build time,
and — once the GPU lock is idle — restarts the service onto the new
version. `APP_VER` controls the target: `dev` disables updates, `stable`
(the default) tracks the latest release, and an exact `vX.Y.Z` pins that
release (even as a downgrade or to replace a dev build). Disable entirely
with `AUTO_UPDATE=false`. Releases are signed by CI with
OpenSSL; the matching public key lives in `internal/update/pubkey.go`
(one-time setup: `openssl genpkey -algorithm ed25519 -out private.pem`,
`openssl pkey -in private.pem -pubout -out public.pem`; private key goes
to the `RELEASE_SIGNING_KEY` repo secret, public key is committed).
`gpu-turnstile --force-update` checks immediately, stages the new binary
and restarts the running service (elevating via UAC only if needed).

### Docker

```sh
docker build -t gpu-turnstile .
docker run --rm -p 11434:11434 -p 8188:8188 \
  -e OLLAMA_URL=http://<workstation-ip>:11435 \
  -e COMFY_URL=http://<workstation-ip>:8189 \
  gpu-turnstile
```

Releases are built by Gitea Actions (`.gitea/workflows/ci.yml`): every push
runs `go vet` and `go test -race`, and pushing a semantic-version tag
`vX.Y.Z` publishes the container image
(`git.rambossek.at/<owner>/gpu-turnstile:vX.Y.Z` plus `:latest`) and a
signed Windows binary attached to a Gitea release. Nothing is built from
branches.

The registry login needs one repository secret (Settings → Actions →
Secrets): `REGISTRY_TOKEN` — an access token with `write:package` scope.
The automatic `GITEA_TOKEN` cannot push packages.

## Development

```sh
go vet ./...
go test -race ./...
```

Go 1.23+; the only external dependency is `golang.org/x/sys` (Windows
service integration, unused in the Linux build). Layout:

```
cmd/gpu-turnstile/main.go  wiring, config, listeners, service + updater
internal/lock/             two-mode lock (LLM readers / image writer, FIFO)
internal/ollama/           ps / unload / warm client
internal/comfy/            history poll / free client
internal/proxy/            handlers for both listeners
internal/metrics/          Prometheus exposition, no dependencies
internal/config/           env + .env file configuration
internal/update/           signed auto-updater
internal/service/          Windows service integration
```