# 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).
- `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.

## Configuration

All configuration is via environment variables; invalid values fail at
startup.

| Var | Default | Meaning |
|---|---|---|
| `LISTEN_OLLAMA` | `:11434` | Ollama-facing listener |
| `LISTEN_COMFY` | `:8188` | ComfyUI-facing listener |
| `OLLAMA_URL` | `http://127.0.0.1:11435` | Ollama upstream |
| `COMFY_URL` | `http://127.0.0.1:8189` | ComfyUI upstream |
| `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 |
| `WARM_MODEL` | _(empty)_ | Model to reload after an image job (off by default) |
| `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 |
| `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 |
| `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) |

## Observability

- `GET /healthz` (both listeners): `{"state":"idle|llm|image","llm_inflight":N,"image_pending":B}`
- `GET /metrics` (Ollama listener): 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.

## Build and run

```sh
go build ./cmd/gpu-turnstile
./gpu-turnstile
```

```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` builds and publishes
`git.rambossek.at/<owner>/gpu-turnstile:vX.Y.Z` (and updates `:latest`).
No images are 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 ./...
```

Stdlib only, Go 1.23+. Layout:

```
cmd/gpu-turnstile/main.go  wiring, config, listeners
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
```