Elide subnet IPConfiguration field when it passes 2000 entries (#4448)

Fixes #4428.

v2/api/network/customizations/virtual_network_subnet_extensions.go

@@ -0,0 +1,52 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+package customizations
+
+import (
+	"context"
+
+	"github.com/go-logr/logr"
+	"github.com/pkg/errors"
+	"sigs.k8s.io/controller-runtime/pkg/conversion"
+
+	network "github.com/Azure/azure-service-operator/v2/api/network/v1api20240301/storage"
+	"github.com/Azure/azure-service-operator/v2/internal/genericarmclient"
+	"github.com/Azure/azure-service-operator/v2/internal/resolver"
+	"github.com/Azure/azure-service-operator/v2/pkg/genruntime"
+	"github.com/Azure/azure-service-operator/v2/pkg/genruntime/extensions"
+)
+
+var _ extensions.PostReconciliationChecker = &PrivateEndpointExtension{}
+
+func (extension *VirtualNetworksSubnetExtension) PostReconcileCheck(
+	_ context.Context,
+	obj genruntime.MetaObject,
+	_ genruntime.MetaObject,
+	_ *resolver.Resolver,
+	_ *genericarmclient.GenericClient,
+	_ logr.Logger,
+	_ extensions.PostReconcileCheckFunc,
+) (extensions.PostReconcileCheckResult, error) {
+	subnet, ok := obj.(*network.VirtualNetworksSubnet)
+	if !ok {
+		return extensions.PostReconcileCheckResult{},
+			errors.Errorf("cannot run on unknown resource type %T, expected *network.VirtualNetworksSubnet", obj)
+	}
+
+	// Type assert that we are the hub type. This will fail to compile if
+	// the hub type has been changed but this extension has not
+	var _ conversion.Hub = subnet
+
+	// Subnets can have a HUGE number of ipConfigurations in some modes. So many that it can cause Kubernetes to be unable
+	// to fit the resource. We have to omit them after some point to avoid blowing out the resource size and causing
+	// kube-apiserver to reject us. See https://github.com/Azure/azure-service-operator/issues/4428.
+
+	// This limit was chosen based on a 300 character long IPConfiguration ID,
+	// which would be 300 bytes in UTF-8. 2000*300 = ~.6mb, which is about around 1/3rd the max allowed size of a
+	// Kubernetes object.
+	if len(subnet.Status.IpConfigurations) > 2000 {
+		subnet.Status.IpConfigurations = nil
+	}
+
+	return extensions.PostReconcileCheckResultSuccess(), nil
+}