fix(distributed): detach cold-load staging from the request context (#10438)

A model not yet loaded on a worker is staged lazily on the inference
request path. Staging a multi-GB model takes minutes - far longer than
any client keeps its HTTP request open - so a browser refresh, an
ingress/LB idle-timeout, or a round-robined retry landing on another
frontend replica cancels the request context and aborts the upload with
"context canceled" mid-transfer. Large models then never finish staging,
so they never load (observed in a 2-replica deployment: both frontends
repeatedly failed to stage a 15.7 GB GGUF, each attempt dying at a
different offset).

Bind the cold load (staging + LoadModel + the per-model advisory lock) to
context.WithoutCancel(ctx): it keeps the request's values (prefix chain)
but drops cancellation/deadline. Each long step keeps its own bound (the
file stager's resume budget, LoadModel's 5m timeout), and the advisory
lock still de-dupes concurrent loaders across replicas.


Assisted-by: Claude:claude-opus-4-8 [Claude Code]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

core/services/nodes/router.go

@@ -359,8 +359,21 @@ func (r *SmartRouter) Route(ctx context.Context, modelID, modelName, backendType
 		}
 	}
 
-	// Step 2: Model not loaded — schedule loading with distributed lock to prevent duplicates
-	loadModel := func() (*RouteResult, error) {
+	// Step 2: Model not loaded — schedule loading with distributed lock to prevent duplicates.
+	//
+	// Detach the cold-load from the caller's context. Staging a model can
+	// transfer multiple GB to a worker, which takes far longer than any client
+	// keeps its HTTP request open — a browser refresh, an ingress/LB idle
+	// timeout, or a round-robined retry landing on another replica all cancel
+	// the request context. If staging were bound to it, the multi-GB upload
+	// aborts with "context canceled" mid-transfer and large models can never
+	// finish staging (the model-load outage). WithoutCancel keeps the request's
+	// values (prefix chain, etc.) but drops its cancellation/deadline. Each
+	// long step still has its own bound (the file stager's resume budget,
+	// LoadModel's 5m timeout), and the per-model advisory lock below de-dupes
+	// concurrent loaders across replicas.
+	loadCtx := context.WithoutCancel(ctx)
+	loadModel := func(ctx context.Context) (*RouteResult, error) {
 		// Re-check after acquiring lock — another request may have loaded it
 		node, nm, err := r.registry.FindAndLockNodeWithModel(ctx, trackingKey, candidateNodeIDs, pref)
 		if err == nil && node != nil {
@@ -433,9 +446,9 @@ func (r *SmartRouter) Route(ctx context.Context, modelID, modelName, backendType
 	if r.db != nil {
 		lockKey := advisorylock.KeyFromString("model-load:" + trackingKey)
 		var result *RouteResult
-		lockErr := advisorylock.WithLockCtx(ctx, r.db, lockKey, func() error {
+		lockErr := advisorylock.WithLockCtx(loadCtx, r.db, lockKey, func() error {
 			var err error
-			result, err = loadModel()
+			result, err = loadModel(loadCtx)
 			return err
 		})
 		if lockErr != nil {
@@ -444,7 +457,7 @@ func (r *SmartRouter) Route(ctx context.Context, modelID, modelName, backendType
 		return result, nil
 	}
 	// No DB (non-distributed) — proceed without lock
-	return loadModel()
+	return loadModel(loadCtx)
 }
 
 // parseSelectorJSON decodes a JSON node selector string into a map.

core/services/nodes/router_staging_context_test.go

@@ -0,0 +1,80 @@
+package nodes
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+
+	"github.com/mudler/LocalAI/core/services/messaging"
+	pb "github.com/mudler/LocalAI/pkg/grpc/proto"
+)
+
+// cancelOnStageStager simulates the triggering HTTP request being abandoned
+// (client disconnect, ingress idle-timeout) the moment a multi-GB file starts
+// staging. It cancels the request context and records whether the context the
+// stager itself received was cancelled as a result.
+type cancelOnStageStager struct {
+	fakeFileStager
+	cancelRequest context.CancelFunc
+	staged        bool
+	ctxErrOnStage error
+}
+
+func (s *cancelOnStageStager) EnsureRemote(ctx context.Context, _, _, key string) (string, error) {
+	s.staged = true
+	// Mid-transfer: the client gives up on the (minutes-long) request.
+	if s.cancelRequest != nil {
+		s.cancelRequest()
+	}
+	// A multi-GB upload must survive this. If staging were bound to the
+	// request context, ctx is now cancelled and the real HTTP stager would
+	// abort with "context canceled" — exactly the production outage.
+	s.ctxErrOnStage = ctx.Err()
+	return "/remote/" + key, nil
+}
+
+var _ = Describe("Route cold-load staging context", func() {
+	It("detaches staging from the request context so a client disconnect cannot abort a multi-GB transfer", func() {
+		// A real model file so stageModelFiles actually calls the stager
+		// (non-existent paths are skipped).
+		tmp := GinkgoT().TempDir()
+		modelFile := filepath.Join(tmp, "big.gguf")
+		Expect(os.WriteFile(modelFile, []byte("weights"), 0o644)).To(Succeed())
+
+		reg := &fakeModelRouter{
+			findAndLockErr: errors.New("not loaded"),
+			findIdleNode:   &BackendNode{ID: "n1", Name: "worker-1", Address: "10.0.0.1:50051"},
+		}
+		backend := &stubBackend{loadResult: &pb.Result{Success: true}}
+		factory := &stubClientFactory{client: backend}
+		unloader := &fakeUnloader{installReply: &messaging.BackendInstallReply{
+			Success: true,
+			Address: "10.0.0.1:9001",
+		}}
+		stager := &cancelOnStageStager{}
+
+		router := NewSmartRouter(reg, SmartRouterOptions{
+			Unloader:      unloader,
+			ClientFactory: factory,
+			FileStager:    stager,
+			// DB nil: no advisory lock, exercises the same detached load ctx.
+		})
+
+		ctx, cancel := context.WithCancel(context.Background())
+		stager.cancelRequest = cancel
+		defer cancel()
+
+		result, err := router.Route(ctx, "big-model", filepath.Join("models", "big.gguf"), "llama-cpp",
+			&pb.ModelOptions{Model: "big.gguf", ModelFile: modelFile}, false)
+
+		Expect(err).ToNot(HaveOccurred())
+		Expect(result).ToNot(BeNil())
+		Expect(stager.staged).To(BeTrue(), "staging must have been attempted")
+		Expect(stager.ctxErrOnStage).ToNot(HaveOccurred(),
+			"staging context must survive cancellation of the triggering request")
+	})
+})