Shoot-dns-service panics when the API discovery fails for core apiservices

[Kristian-ZH]

What happened:
We found an shoot-dns-service pod which was constantly failing with panic:

2022-09-29 12:03:23	{"log":"panic: runtime error: invalid memory address or nil pointer dereference"}
2022-09-29 12:03:23	{"log":"[signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x12a4624]"}
2022-09-29 12:03:23	{"log":"goroutine 1 [running]:"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/resources.(*ResourceInfos).doUpdateGroup.func1(0xc0008c06c0, {{{0x0, 0x0}, {0x0, 0x0}}, {0xc000c36210, 0x11}, {0xc00059a800, 0x2, 0x4}, ...}, ...)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/resources/info.go:201 +0x1e4"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/resources.(*ResourceInfos).doUpdateGroup(0x4e3?, 0xc000058cc0?, {{{0x0, 0x0}, {0x0, 0x0}}, {0xc000c36210, 0x11}, {0xc00059a800, 0x2, ...}, ...})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/resources/info.go:221 +0x19a"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/resources.(*ResourceInfos).update(0xc0008c06c0, 0xc0009be220)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/resources/info.go:162 +0x6ee"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/resources.NewResourceInfos({0x24cd720?, 0xc0008ae500}, 0xc000bbd800)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/resources/info.go:102 +0x117"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/resources.NewResourceContext({0x24c47b8, 0xc000bb84b0}, {0x24cd720?, 0xc0008ae500}, 0xc0002858f0, 0x0)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/resources/context.go:55 +0x154"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager/cluster.(*_Cluster).setup(0xc0008ae500, {0x7?, 0x0?})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/cluster/cluster.go:187 +0x50"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager/cluster.CreateClusterForScheme({0x24c47b8?, 0xc000bb84b0}, {0x24ce940, 0xc00050f230}, {0x24cd780, 0xc000bb2500}, {0x7ffc656340b9, 0x53}, 0xc000bcc000, 0x0)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/cluster/cluster.go:267 +0x615"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager/cluster.CreateCluster({0x24c47b8, 0xc000bb84b0}, {0x24ce940, 0xc00050f230}, {0x24cd780?, 0xc000bb2500?}, {0x7ffc656340b9, 0x53}, 0xc0001ea770)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/cluster/cluster.go:248 +0x4e7"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager/cluster.(*_Definitions).create(0xc000447860, {0x24c47b8, 0xc000bb84b0}, {0x24ce940?, 0xc00050f230?}, 0xc0001ea770, {0x24cd780, 0xc0003ed360})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/cluster/definition.go:130 +0x305"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager/cluster.(*_Definitions).handleCluster(0xc000447860, {0x24c47b8, 0xc000bb84b0}, {0x24ce940?, 0xc00050f230?}, 0xc00048ed20, 0xc000bb1000, 0x26?, {0x20c4faa, 0x7})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/cluster/definition.go:202 +0x349"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager/cluster.(*_Definitions).CreateClusters(0xc000447860, {0x24c47b8, 0xc000bb84b0}, {0x24ce940?, 0xc00050f230?}, 0x20e1f45?, {0x24c4940?, 0xc000bb7e20?}, 0xc000bb84e0)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/cluster/definition.go:166 +0x57a"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager.NewControllerManager({0x24c47b8, 0xc000a34270?}, {0x24cb070?, 0xc0003ed6d0})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/controllermanager.go:149 +0xe28"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager.runCM.func1()"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/main.go:140 +0xf2"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/run.Run({0x24c47b8, 0xc000a34270}, 0xc0009bf918)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/run/run.go:45 +0x299"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager.runCM({0x24c47b8?, 0xc000a34270?}, {0x24cb070?, 0xc0003ed6d0?})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/main.go:138 +0x65"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager.NewCommand.func1(0xc000a3af00?, {0x20c5d02?, 0x12?, 0x13?})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/main.go:125 +0x193"}
2022-09-29 12:03:23	{"log":"github.com/spf13/cobra.(*Command).execute(0xc000a3af00, {0xc0001a2010, 0x12, 0x13})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/spf13/cobra/command.go:856 +0x67c"}
2022-09-29 12:03:23	{"log":"github.com/spf13/cobra.(*Command).ExecuteC(0xc000a3af00)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/spf13/cobra/command.go:974 +0x3bd"}
2022-09-29 12:03:23	{"log":"github.com/spf13/cobra.(*Command).Execute(...)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/spf13/cobra/command.go:902"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager.Configuration.Start({{0x20e1064, 0x16}, {0x20c55d8, 0x7}, {0x24c4a58, 0xc0004a9a60}, {0x24b6fc8, 0xc000407538}, {0x0}, 0xc0004477a0, ...}, ...)"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/main.go:98 +0x30e"}
2022-09-29 12:03:23	{"log":"github.com/gardener/controller-manager-library/pkg/controllermanager.Start({0x20e1064, 0x16}, {0x20e1038, 0x16}, {0x20c55d8?, 0x406719?}, {0xc0009bff58, 0x1, 0x0?})"}
2022-09-29 12:03:23	{"log":"\t/build/vendor/github.com/gardener/controller-manager-library/pkg/controllermanager/main.go:38 +0x158"}
2022-09-29 12:03:23	{"log":"main.main()"}
2022-09-29 12:03:23	{"log":"\t/build/cmd/compound/main.go:89 +0xf0"}

The kubectl api-resources was failing with:

error: unable to retrieve the complete list of server APIs: admissionregistration.k8s.io/v1beta1: the server could not find the requested resource, apiextensions.k8s.io/v1beta1: the server could not find the requested resource, authentication.k8s.io/v1beta1: the server could not find the requested resource, authorization.k8s.io/v1beta1: the server could not find the requested resource, certificates.k8s.io/v1beta1: the server could not find the requested resource, coordination.k8s.io/v1beta1: the server could not find the requested resource, extensions/v1beta1: the server could not find the requested resource, networking.k8s.io/v1beta1: the server could not find the requested resource, rbac.authorization.k8s.io/v1beta1: the server could not find the requested resource, scheduling.k8s.io/v1beta1: the server could not find the requested resource

This issue was workarounded by restarting the kube-apiserver.

What you expected to happen:
Shoot-dns-service pod should not panic in this situation .

How to reproduce it (as minimally and precisely as possible):
We were not able to reproduce it locally.

Anything else we need to know:

Environment:

/cc @dimitar-kostadinov @ialidzhikov