fix(distributed): return empty backend list for agent nodes instead of failing backend.list (#10545)

Opening an AGENT-type worker node's detail page errored with
"failed to list backends on node" / NATS "nodes.<id>.backend.list:
no responders available". Agent workers only subscribe to agent.*,
jobs.*, mcp.* and <prefix>.backend.stop; they never subscribe to
backend.list, so the per-node ListBackendsOnNodeEndpoint request had
no responder and timed out.

The aggregate cluster-wide list already guards this in
managers_distributed.go (skip nodes whose NodeType is set and not
"backend"). The single-node endpoint lacked the same guard. Thread the
NodeRegistry into ListBackendsOnNodeEndpoint and short-circuit to an
empty (non-nil) list for non-backend node types before issuing the
doomed NATS request, mirroring the aggregate-list gate so both views
stay consistent.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Assisted-by: Claude:claude-opus-4-8 [Claude Code]

core/http/endpoints/localai/nodes.go

@@ -25,6 +25,7 @@ import (
 	"github.com/mudler/LocalAI/core/http/auth"
 	"github.com/mudler/LocalAI/core/schema"
 	"github.com/mudler/LocalAI/core/services/galleryop"
+	"github.com/mudler/LocalAI/core/services/messaging"
 	"github.com/mudler/LocalAI/core/services/nodes"
 	"github.com/mudler/LocalAI/core/services/nodes/prefixcache"
 	"github.com/mudler/LocalAI/pkg/httpclient"
@@ -550,12 +551,23 @@ func DeleteBackendOnNodeEndpoint(unloader nodes.NodeCommandSender) echo.HandlerF
 }
 
 // ListBackendsOnNodeEndpoint lists installed backends on a worker node via NATS.
-func ListBackendsOnNodeEndpoint(unloader nodes.NodeCommandSender) echo.HandlerFunc {
+func ListBackendsOnNodeEndpoint(unloader nodes.NodeCommandSender, registry *nodes.NodeRegistry) echo.HandlerFunc {
 	return func(c echo.Context) error {
+		nodeID := c.Param("id")
+		// Agent-type workers don't run backends and never subscribe to the
+		// nodes.<id>.backend.list NATS subject, so the request would hang
+		// until timeout with "no responders". Their backend list is simply
+		// empty. Mirror the aggregate-list guard in managers_distributed.go
+		// (skip nodes whose NodeType is set and not "backend") so the
+		// single-node and cluster-wide views stay consistent.
+		if node, err := registry.Get(c.Request().Context(), nodeID); err == nil {
+			if node.NodeType != "" && node.NodeType != nodes.NodeTypeBackend {
+				return c.JSON(http.StatusOK, []messaging.NodeBackendInfo{})
+			}
+		}
 		if unloader == nil {
 			return c.JSON(http.StatusServiceUnavailable, nodeError(http.StatusServiceUnavailable, "NATS not configured"))
 		}
-		nodeID := c.Param("id")
 		reply, err := unloader.ListBackends(nodeID)
 		if err != nil {
 			xlog.Error("Failed to list backends on node", "node", nodeID, "error", err)

core/http/endpoints/localai/nodes_backends_list_test.go

@@ -0,0 +1,103 @@
+package localai
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+
+	"github.com/labstack/echo/v4"
+	"github.com/mudler/LocalAI/core/services/messaging"
+	"github.com/mudler/LocalAI/core/services/nodes"
+	"github.com/mudler/LocalAI/core/services/testutil"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+// stubNodeCommandSender records whether ListBackends was invoked so the test can
+// assert the endpoint short-circuits (no NATS request) for agent-type nodes.
+type stubNodeCommandSender struct {
+	listBackendsCalled bool
+}
+
+func (s *stubNodeCommandSender) InstallBackend(_, _, _, _, _, _, _ string, _ int, _ string, _ func(messaging.BackendInstallProgressEvent)) (*messaging.BackendInstallReply, error) {
+	return &messaging.BackendInstallReply{}, nil
+}
+
+func (s *stubNodeCommandSender) UpgradeBackend(_, _, _, _, _, _ string, _ int, _ string, _ func(messaging.BackendInstallProgressEvent)) (*messaging.BackendUpgradeReply, error) {
+	return &messaging.BackendUpgradeReply{}, nil
+}
+
+func (s *stubNodeCommandSender) DeleteBackend(_, _ string) (*messaging.BackendDeleteReply, error) {
+	return &messaging.BackendDeleteReply{Success: true}, nil
+}
+
+func (s *stubNodeCommandSender) ListBackends(_ string) (*messaging.BackendListReply, error) {
+	s.listBackendsCalled = true
+	return &messaging.BackendListReply{Backends: []messaging.NodeBackendInfo{{Name: "llama-cpp"}}}, nil
+}
+
+func (s *stubNodeCommandSender) StopBackend(_, _ string) error { return nil }
+
+func (s *stubNodeCommandSender) UnloadModelOnNode(_, _ string) error { return nil }
+
+var _ = Describe("ListBackendsOnNodeEndpoint", func() {
+	var registry *nodes.NodeRegistry
+
+	BeforeEach(func() {
+		db := testutil.SetupTestDB()
+		var err error
+		registry, err = nodes.NewNodeRegistry(db)
+		Expect(err).ToNot(HaveOccurred())
+	})
+
+	callEndpoint := func(unloader nodes.NodeCommandSender, nodeID string) *httptest.ResponseRecorder {
+		e := echo.New()
+		req := httptest.NewRequest(http.MethodGet, "/", nil)
+		rec := httptest.NewRecorder()
+		c := e.NewContext(req, rec)
+		c.SetParamNames("id")
+		c.SetParamValues(nodeID)
+		handler := ListBackendsOnNodeEndpoint(unloader, registry)
+		Expect(handler(c)).To(Succeed())
+		return rec
+	}
+
+	It("returns an empty list for an agent node without issuing a NATS request", func() {
+		ctx := context.Background()
+		node := &nodes.BackendNode{Name: "agent-1", NodeType: nodes.NodeTypeAgent}
+		Expect(registry.Register(ctx, node, true)).To(Succeed())
+
+		stub := &stubNodeCommandSender{}
+		rec := callEndpoint(stub, node.ID)
+
+		Expect(rec.Code).To(Equal(http.StatusOK))
+		Expect(stub.listBackendsCalled).To(BeFalse(),
+			"agent workers don't subscribe to backend.list; the endpoint must not issue the doomed NATS request")
+
+		var list []messaging.NodeBackendInfo
+		Expect(json.Unmarshal(rec.Body.Bytes(), &list)).To(Succeed())
+		Expect(list).To(BeEmpty())
+		// Must be `[]`, not `null`, so the UI can render it.
+		Expect(rec.Body.String()).To(ContainSubstring("[]"))
+	})
+
+	It("consults the unloader (NATS) for a backend node", func() {
+		ctx := context.Background()
+		node := &nodes.BackendNode{Name: "backend-1", NodeType: nodes.NodeTypeBackend, Address: "10.0.0.1:50051"}
+		Expect(registry.Register(ctx, node, true)).To(Succeed())
+
+		stub := &stubNodeCommandSender{}
+		rec := callEndpoint(stub, node.ID)
+
+		Expect(rec.Code).To(Equal(http.StatusOK))
+		Expect(stub.listBackendsCalled).To(BeTrue(),
+			"backend nodes must still be queried over NATS")
+
+		var list []messaging.NodeBackendInfo
+		Expect(json.Unmarshal(rec.Body.Bytes(), &list)).To(Succeed())
+		Expect(list).To(HaveLen(1))
+		Expect(list[0].Name).To(Equal("llama-cpp"))
+	})
+})

core/http/routes/nodes.go

@@ -88,7 +88,7 @@ func RegisterNodeAdminRoutes(e *echo.Echo, registry *nodes.NodeRegistry, unloade
 	admin.POST("/:id/approve", localai.ApproveNodeEndpoint(registry, authDB, hmacSecret, natsCfg))
 
 	// Backend management on workers
-	admin.GET("/:id/backends", localai.ListBackendsOnNodeEndpoint(unloader))
+	admin.GET("/:id/backends", localai.ListBackendsOnNodeEndpoint(unloader, registry))
 	admin.POST("/:id/backends/install", localai.InstallBackendOnNodeEndpoint(unloader, galleryService, opcache, appConfig))
 	admin.POST("/:id/backends/delete", localai.DeleteBackendOnNodeEndpoint(unloader))