gpulock: GPU arbitration proxy for Ollama + ComfyUI
Implements SPEC.md: two listeners, one writer-preferring two-mode lock, Ollama unload before image jobs, ComfyUI history polling + VRAM free, optional model warm-up, healthz/metrics endpoints, streaming-safe reverse proxies, Dockerfile and Gitea Actions CI.
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mram
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// Package proxy contains the HTTP handlers for both gpulock listeners:
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// reverse proxies to Ollama and ComfyUI with GPU lock arbitration in front
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// of the endpoints that load models.
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package proxy
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import (
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"bytes"
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"context"
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"encoding/json"
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"errors"
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"fmt"
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"log/slog"
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"net/http"
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"net/http/httputil"
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"net/url"
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"time"
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"gpu-turnstile/internal/comfy"
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"gpu-turnstile/internal/lock"
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"gpu-turnstile/internal/metrics"
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"gpu-turnstile/internal/ollama"
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)
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// captureLimit bounds how much of a /prompt response body is buffered while
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// looking for prompt_id. The body still passes through to the client
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// unchanged regardless of size.
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const captureLimit = 64 * 1024
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// Config wires a Server.
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type Config struct {
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OllamaURL string
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ComfyURL string
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Lock *lock.Lock
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Ollama *ollama.Client
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Comfy *comfy.Client
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Metrics *metrics.Metrics
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Log *slog.Logger
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LLMWaitTimeout time.Duration
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UnloadTimeout time.Duration
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JobTimeout time.Duration
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WarmModel string
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}
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// Server serves both gpulock listeners.
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type Server struct {
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cfg Config
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log *slog.Logger
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ollamaProxy *httputil.ReverseProxy
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comfyProxy *httputil.ReverseProxy
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}
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// New builds a Server, validating the upstream URLs.
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func New(cfg Config) (*Server, error) {
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ollamaURL, err := url.Parse(cfg.OllamaURL)
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if err != nil || ollamaURL.Scheme == "" || ollamaURL.Host == "" {
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return nil, fmt.Errorf("invalid OLLAMA_URL %q", cfg.OllamaURL)
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}
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comfyURL, err := url.Parse(cfg.ComfyURL)
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if err != nil || comfyURL.Scheme == "" || comfyURL.Host == "" {
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return nil, fmt.Errorf("invalid COMFY_URL %q", cfg.ComfyURL)
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}
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log := cfg.Log
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if log == nil {
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log = slog.Default()
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}
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return &Server{
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cfg: cfg,
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log: log,
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ollamaProxy: newReverseProxy(ollamaURL, log.With("upstream", "ollama")),
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comfyProxy: newReverseProxy(comfyURL, log.With("upstream", "comfy")),
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}, nil
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}
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func newReverseProxy(target *url.URL, log *slog.Logger) *httputil.ReverseProxy {
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return &httputil.ReverseProxy{
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Rewrite: func(pr *httputil.ProxyRequest) {
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pr.SetURL(target)
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pr.SetXForwarded()
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},
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// Flush after every write so NDJSON/SSE streams and websocket
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// upgrades pass through unbuffered.
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FlushInterval: -1,
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ErrorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
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log.Warn("upstream error", "path", r.URL.Path, "err", err)
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http.Error(w, "upstream unavailable", http.StatusBadGateway)
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},
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}
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}
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func (s *Server) writeHealthz(w http.ResponseWriter) {
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state, n, pending := s.cfg.Lock.Snapshot()
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w.Header().Set("Content-Type", "application/json")
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json.NewEncoder(w).Encode(map[string]any{
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"state": state,
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"llm_inflight": n,
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"image_pending": pending,
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})
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}
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func (s *Server) writeMetrics(w http.ResponseWriter) {
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state, n, pending := s.cfg.Lock.Snapshot()
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w.Header().Set("Content-Type", "text/plain; version=0.0.4")
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s.cfg.Metrics.Render(w, string(state), n, pending)
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}
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// llmPaths are the Ollama endpoints that load models into VRAM and therefore
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// take the LLM lock. Everything else passes through unlocked.
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var llmPaths = map[string]bool{
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"/api/generate": true,
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"/api/chat": true,
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"/api/embed": true,
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"/api/embeddings": true,
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"/v1/chat/completions": true,
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"/v1/completions": true,
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"/v1/embeddings": true,
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}
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func isLLMRequest(r *http.Request) bool {
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return r.Method == http.MethodPost && llmPaths[r.URL.Path]
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}
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// OllamaHandler serves the Ollama-facing listener.
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func (s *Server) OllamaHandler() http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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switch r.URL.Path {
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case "/healthz":
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s.writeHealthz(w)
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return
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case "/metrics":
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s.writeMetrics(w)
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return
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}
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if !isLLMRequest(r) {
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s.ollamaProxy.ServeHTTP(w, r)
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return
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}
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start := time.Now()
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wctx, cancel := context.WithTimeout(r.Context(), s.cfg.LLMWaitTimeout)
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err := s.cfg.Lock.AcquireLLM(wctx)
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cancel()
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s.cfg.Metrics.ObserveLockWait("llm", time.Since(start).Seconds())
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if err != nil {
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if errors.Is(err, context.DeadlineExceeded) && r.Context().Err() == nil {
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http.Error(w, "GPU busy: timed out waiting for the lock", http.StatusServiceUnavailable)
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}
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return
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}
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defer s.cfg.Lock.ReleaseLLM()
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s.ollamaProxy.ServeHTTP(w, r)
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})
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}
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// ComfyHandler serves the ComfyUI-facing listener.
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func (s *Server) ComfyHandler() http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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if r.URL.Path == "/healthz" {
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s.writeHealthz(w)
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return
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}
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if r.Method == http.MethodPost && r.URL.Path == "/prompt" {
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s.handlePrompt(w, r)
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return
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}
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s.comfyProxy.ServeHTTP(w, r)
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})
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}
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// captureWriter passes the response through unchanged while recording the
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// status code and the first captureLimit bytes of the body.
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type captureWriter struct {
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http.ResponseWriter
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status int
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buf bytes.Buffer
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}
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func (w *captureWriter) WriteHeader(code int) {
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w.status = code
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w.ResponseWriter.WriteHeader(code)
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}
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func (w *captureWriter) Write(p []byte) (int, error) {
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if w.buf.Len() < captureLimit {
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w.buf.Write(p)
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}
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return w.ResponseWriter.Write(p)
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}
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func (w *captureWriter) Flush() {
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if f, ok := w.ResponseWriter.(http.Flusher); ok {
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f.Flush()
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}
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}
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func (w *captureWriter) Unwrap() http.ResponseWriter { return w.ResponseWriter }
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// handlePrompt implements the image job flow from the spec: acquire the
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// image lock, unload Ollama, forward to ComfyUI, then track the job in the
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// background and free VRAM before releasing the lock.
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func (s *Server) handlePrompt(w http.ResponseWriter, r *http.Request) {
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log := s.log.With("op", "image")
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start := time.Now()
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if err := s.cfg.Lock.AcquireImage(r.Context()); err != nil {
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if errors.Is(err, context.DeadlineExceeded) {
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http.Error(w, "GPU busy: timed out waiting for the lock", http.StatusServiceUnavailable)
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}
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return
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}
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s.cfg.Metrics.ObserveLockWait("image", time.Since(start).Seconds())
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log.Info("image lock acquired")
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uctx, ucancel := context.WithTimeout(r.Context(), s.cfg.UnloadTimeout)
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elapsed, uerr := s.cfg.Ollama.UnloadAll(uctx)
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ucancel()
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s.cfg.Metrics.ObserveUnload(elapsed.Seconds())
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switch {
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case r.Context().Err() != nil:
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s.cfg.Lock.ReleaseImage()
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return
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case uerr != nil:
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// Degrade, don't fail the user's request on a misbehaving neighbour.
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log.Warn("ollama unload incomplete; continuing", "err", uerr)
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default:
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log.Info("ollama models unloaded", "seconds", elapsed.Seconds())
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}
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cw := &captureWriter{ResponseWriter: w, status: http.StatusOK}
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s.comfyProxy.ServeHTTP(cw, r)
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var accepted struct {
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PromptID string `json:"prompt_id"`
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}
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if cw.status == http.StatusOK {
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_ = json.Unmarshal(cw.buf.Bytes(), &accepted)
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}
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if accepted.PromptID == "" {
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log.Info("prompt not accepted; releasing image lock", "status", cw.status)
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s.cfg.Lock.ReleaseImage()
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return
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}
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s.cfg.Metrics.IncImageJobs()
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go s.finishImageJob(accepted.PromptID)
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}
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// finishImageJob runs after the prompt has been accepted by ComfyUI: wait
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// for the job to finish, free ComfyUI's models, release the lock, and
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// optionally warm the chat model.
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func (s *Server) finishImageJob(promptID string) {
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log := s.log.With("prompt_id", promptID)
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log.Info("image job running")
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ctx, cancel := context.WithTimeout(context.Background(), s.cfg.JobTimeout)
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err := s.cfg.Comfy.WaitJob(ctx, promptID)
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cancel()
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if err != nil {
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log.Warn("image job did not complete cleanly; releasing lock anyway", "err", err)
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} else {
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log.Info("image job completed")
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}
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freeCtx, freeCancel := context.WithTimeout(context.Background(), 30*time.Second)
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if err := s.cfg.Comfy.Free(freeCtx); err != nil {
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log.Warn("failed to free ComfyUI models", "err", err)
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}
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freeCancel()
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s.cfg.Lock.ReleaseImage()
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log.Info("image lock released")
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if s.cfg.WarmModel != "" {
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if state, _, _ := s.cfg.Lock.Snapshot(); state == lock.StateIdle {
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wctx, wcancel := context.WithTimeout(context.Background(), 2*time.Minute)
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if err := s.cfg.Ollama.Warm(wctx, s.cfg.WarmModel); err != nil {
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log.Warn("warm model reload failed", "model", s.cfg.WarmModel, "err", err)
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} else {
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log.Info("warm model reloaded", "model", s.cfg.WarmModel)
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}
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wcancel()
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}
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}
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}
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