feat: Add fallback to capacity filter and external customer filter

internal/scheduling/nova/plugins/filters/filter_external_customer.go

@@ -37,8 +37,8 @@ func (s *FilterExternalCustomerStep) Run(traceLog *slog.Logger, request api.Exte
 	result := s.IncludeAllHostsFromRequest(request)
 	domainName, err := request.Spec.Data.GetSchedulerHintStr("domain_name")
 	if err != nil {
-		traceLog.Error("failed to get domain_name scheduler hint", "error", err)
-		return nil, err
+		traceLog.Error("failed to get domain_name scheduler hint, skipping filter", "error", err)
+		return result, nil
 	}
 	if slices.Contains(s.Options.CustomerIgnoredDomainNames, domainName) {
 		traceLog.Info("domain is no external customer domain, skipping filter", "domain", domainName)

internal/scheduling/nova/plugins/filters/filter_external_customer_test.go

@@ -245,7 +245,7 @@ func TestFilterExternalCustomerStep_Run(t *testing.T) {
 			filteredHosts: []string{"host3"},
 		},
 		{
-			name: "Missing domain_name in scheduler hints - error",
+			name: "Missing domain_name in scheduler hints - skips filter, all hosts pass",
 			opts: FilterExternalCustomerStepOpts{
 				CustomerDomainNamePrefixes: []string{"ext-"},
 			},
@@ -257,12 +257,14 @@ func TestFilterExternalCustomerStep_Run(t *testing.T) {
 				},
 				Hosts: []api.ExternalSchedulerHost{
 					{ComputeHost: "host1"},
+					{ComputeHost: "host3"},
 				},
 			},
-			expectError: true,
+			expectedHosts: []string{"host1", "host3"},
+			filteredHosts: []string{},
 		},
 		{
-			name: "Nil scheduler hints - error",
+			name: "Nil scheduler hints - skips filter, all hosts pass",
 			opts: FilterExternalCustomerStepOpts{
 				CustomerDomainNamePrefixes: []string{"ext-"},
 			},
@@ -274,9 +276,11 @@ func TestFilterExternalCustomerStep_Run(t *testing.T) {
 				},
 				Hosts: []api.ExternalSchedulerHost{
 					{ComputeHost: "host1"},
+					{ComputeHost: "host2"},
 				},
 			},
-			expectError: true,
+			expectedHosts: []string{"host1", "host2"},
+			filteredHosts: []string{},
 		},
 		{
 			name: "Case sensitive prefix matching",

internal/scheduling/nova/plugins/filters/filter_has_enough_capacity.go

@@ -56,15 +56,14 @@ func (s *FilterHasEnoughCapacity) Run(traceLog *slog.Logger, request api.Externa
 		return nil, err
 	}
 	for _, hv := range hvs.Items {
-		// This case would be caught below, but we want to log this explicitly.
 		if hv.Status.EffectiveCapacity == nil {
-			traceLog.Warn("hypervisor with nil effective capacity, skipping", "host", hv.Name)
-			continue
+			traceLog.Warn("hypervisor with nil effective capacity, use capacity instead (overprovisioning not considered)", "host", hv.Name)
+			freeResourcesByHost[hv.Name] = hv.Status.Capacity
+		} else {
+			// Start with the total effective capacity which is capacity * overcommit ratio.
+			freeResourcesByHost[hv.Name] = hv.Status.EffectiveCapacity
 		}
 
-		// Start with the total effective capacity which is capacity * overcommit ratio.
-		freeResourcesByHost[hv.Name] = hv.Status.EffectiveCapacity
-
 		// Subtract allocated resources.
 		for resourceName, allocated := range hv.Status.Allocation {
 			free, ok := freeResourcesByHost[hv.Name][resourceName]

internal/scheduling/nova/plugins/filters/filter_has_enough_capacity_test.go

@@ -51,6 +51,49 @@ func newHypervisor(name, cpuCap, cpuAlloc, memCap, memAlloc string) *hv1.Hypervi
 	}
 }
 
+// newHypervisorWithCapacityOnly creates a hypervisor with only Capacity set (no EffectiveCapacity).
+func newHypervisorWithCapacityOnly(name, cpuCap, memCap string) *hv1.Hypervisor {
+	return &hv1.Hypervisor{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: name,
+		},
+		Status: hv1.HypervisorStatus{
+			Capacity: map[hv1.ResourceName]resource.Quantity{
+				hv1.ResourceCPU:    resource.MustParse(cpuCap),
+				hv1.ResourceMemory: resource.MustParse(memCap),
+			},
+			Allocation: map[hv1.ResourceName]resource.Quantity{
+				hv1.ResourceCPU:    resource.MustParse("0"),
+				hv1.ResourceMemory: resource.MustParse("0"),
+			},
+		},
+	}
+}
+
+// newHypervisorWithBothCapacities creates a hypervisor with both Capacity and EffectiveCapacity set.
+// EffectiveCapacity is typically >= Capacity due to overcommit ratio.
+func newHypervisorWithBothCapacities(name, cpuCap, cpuEffCap, memCap, memEffCap string) *hv1.Hypervisor {
+	return &hv1.Hypervisor{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: name,
+		},
+		Status: hv1.HypervisorStatus{
+			Capacity: map[hv1.ResourceName]resource.Quantity{
+				hv1.ResourceCPU:    resource.MustParse(cpuCap),
+				hv1.ResourceMemory: resource.MustParse(memCap),
+			},
+			EffectiveCapacity: map[hv1.ResourceName]resource.Quantity{
+				hv1.ResourceCPU:    resource.MustParse(cpuEffCap),
+				hv1.ResourceMemory: resource.MustParse(memEffCap),
+			},
+			Allocation: map[hv1.ResourceName]resource.Quantity{
+				hv1.ResourceCPU:    resource.MustParse("0"),
+				hv1.ResourceMemory: resource.MustParse("0"),
+			},
+		},
+	}
+}
+
 func newCommittedReservation(
 	name, targetHost, observedHost, projectID, flavorName, flavorGroup, cpu, memory string,
 	specAllocations map[string]v1alpha1.CommittedResourceAllocation, // Spec allocations for CR
@@ -440,7 +483,7 @@ func TestFilterHasEnoughCapacity_ReservationTypes(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			objects := make([]client.Object, 0, len(hypervisors)+len(tt.reservations))
 			for _, h := range hypervisors {
-				objects = append(objects, h)
+				objects = append(objects, h.DeepCopy())
 			}
 			for _, r := range tt.reservations {
 				objects = append(objects, r)
@@ -469,3 +512,87 @@ func TestFilterHasEnoughCapacity_ReservationTypes(t *testing.T) {
 		})
 	}
 }
+
+func TestFilterHasEnoughCapacity_NilEffectiveCapacityFallback(t *testing.T) {
+	scheme := buildTestScheme(t)
+
+	tests := []struct {
+		name          string
+		hypervisors   []*hv1.Hypervisor
+		request       api.ExternalSchedulerRequest
+		expectedHosts []string
+		filteredHosts []string
+	}{
+		{
+			name: "Hypervisor with nil EffectiveCapacity uses Capacity fallback",
+			hypervisors: []*hv1.Hypervisor{
+				newHypervisor("host1", "16", "8", "32Gi", "16Gi"),    // has EffectiveCapacity: 8 CPU free, 16Gi free
+				newHypervisorWithCapacityOnly("host2", "8", "16Gi"),  // nil EffectiveCapacity, uses Capacity: 8 CPU free, 16Gi free
+				newHypervisorWithCapacityOnly("host3", "2", "4Gi"),   // nil EffectiveCapacity, uses Capacity: 2 CPU free (not enough)
+				newHypervisorWithCapacityOnly("host4", "16", "32Gi"), // nil EffectiveCapacity, uses Capacity: 16 CPU free, 32Gi free
+			},
+			request:       newNovaRequest("instance-123", "project-A", "m1.small", "gp-1", 4, "8Gi", false, []string{"host1", "host2", "host3", "host4"}),
+			expectedHosts: []string{"host1", "host2", "host4"},
+			filteredHosts: []string{"host3"},
+		},
+		{
+			name: "All hypervisors with nil EffectiveCapacity use Capacity fallback",
+			hypervisors: []*hv1.Hypervisor{
+				newHypervisorWithCapacityOnly("host1", "8", "16Gi"),
+				newHypervisorWithCapacityOnly("host2", "4", "8Gi"),
+			},
+			request:       newNovaRequest("instance-123", "project-A", "m1.small", "gp-1", 4, "8Gi", false, []string{"host1", "host2"}),
+			expectedHosts: []string{"host1", "host2"},
+			filteredHosts: []string{},
+		},
+		{
+			name: "EffectiveCapacity used when both are set (overcommit scenario)",
+			hypervisors: []*hv1.Hypervisor{
+				// host1: Capacity=8 CPU, EffectiveCapacity=16 CPU (2x overcommit)
+				// With Capacity only: 8 free -> passes
+				// With EffectiveCapacity: 16 free -> passes (more capacity available)
+				newHypervisorWithBothCapacities("host1", "8", "16", "16Gi", "32Gi"),
+				// host2: Capacity=4 CPU, EffectiveCapacity=8 CPU (2x overcommit)
+				// With Capacity only: 4 free -> would be filtered (need 5)
+				// With EffectiveCapacity: 8 free -> passes
+				newHypervisorWithBothCapacities("host2", "4", "8", "8Gi", "16Gi"),
+				// host3: Capacity=4 CPU, EffectiveCapacity=4 CPU (no overcommit)
+				// Both: 4 free -> filtered (need 5)
+				newHypervisorWithBothCapacities("host3", "4", "4", "8Gi", "8Gi"),
+			},
+			request:       newNovaRequest("instance-123", "project-A", "m1.small", "gp-1", 5, "8Gi", false, []string{"host1", "host2", "host3"}),
+			expectedHosts: []string{"host1", "host2"},
+			filteredHosts: []string{"host3"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			objects := make([]client.Object, 0, len(tt.hypervisors))
+			for _, h := range tt.hypervisors {
+				objects = append(objects, h.DeepCopy())
+			}
+
+			step := &FilterHasEnoughCapacity{}
+			step.Client = fake.NewClientBuilder().WithScheme(scheme).WithObjects(objects...).Build()
+			step.Options = FilterHasEnoughCapacityOpts{LockReserved: false}
+
+			result, err := step.Run(slog.Default(), tt.request)
+			if err != nil {
+				t.Fatalf("expected no error, got %v", err)
+			}
+
+			for _, host := range tt.expectedHosts {
+				if _, ok := result.Activations[host]; !ok {
+					t.Errorf("expected host %s to be present in activations, but got %+v", host, result.Activations)
+				}
+			}
+
+			for _, host := range tt.filteredHosts {
+				if _, ok := result.Activations[host]; ok {
+					t.Errorf("expected host %s to be filtered out", host)
+				}
+			}
+		})
+	}
+}