Introduce .spec.schedulerName in Shoot API (gardener#8261)

* Introduce `.spec.schedulerName` in Shoot API

* Address review comments

* Address review comments (II)

* Address review comment (III)

docs/api-reference/core.md

@@ -1841,6 +1841,20 @@ ControlPlane
 <p>ControlPlane contains general settings for the control plane of the shoot.</p>
 </td>
 </tr>
+<tr>
+<td>
+<code>schedulerName</code></br>
+<em>
+string
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>SchedulerName is the name of the responsible scheduler which schedules the shoot.
+If not specified, the default scheduler takes over.
+This field is immutable.</p>
+</td>
+</tr>
 </table>
 </td>
 </tr>
@@ -10909,6 +10923,20 @@ ControlPlane
 <p>ControlPlane contains general settings for the control plane of the shoot.</p>
 </td>
 </tr>
+<tr>
+<td>
+<code>schedulerName</code></br>
+<em>
+string
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>SchedulerName is the name of the responsible scheduler which schedules the shoot.
+If not specified, the default scheduler takes over.
+This field is immutable.</p>
+</td>
+</tr>
 </tbody>
 </table>
 <h3 id="core.gardener.cloud/v1beta1.ShootStateSpec">ShootStateSpec
@@ -11535,6 +11563,20 @@ ControlPlane
 <p>ControlPlane contains general settings for the control plane of the shoot.</p>
 </td>
 </tr>
+<tr>
+<td>
+<code>schedulerName</code></br>
+<em>
+string
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>SchedulerName is the name of the responsible scheduler which schedules the shoot.
+If not specified, the default scheduler takes over.
+This field is immutable.</p>
+</td>
+</tr>
 </table>
 </td>
 </tr>

docs/concepts/scheduler.md

@@ -87,7 +87,14 @@ The region does not matter, i.e., `testing` shoots may also be scheduled on a se
 The `shoots/binding` subresource is used to bind a `Shoot` to a `Seed`. On creation of a shoot cluster/s, the scheduler updates the binding automatically if an appropriate seed cluster is available.
 Only an operator with the necessary RBAC can update this binding manually. This can be done by changing the `.spec.seedName` of the shoot. However, if a different seed is already assigned to the shoot, this will trigger a control-plane migration. For required steps, please see [Triggering the Migration](../operations/control_plane_migration.md#triggering-the-migration).
 
+## `spec.schedulerName` Field in the `Shoot` Specification
+
+Similar to the `spec.schedulerName` field in `Pod`s, the `Shoot` specification has an optional `.spec.schedulerName` field. If this field is set on creation, only the scheduler which relates to the configured name is responsible for scheduling the shoot.
+The `default-scheduler` name is reserved for the default scheduler of Gardener.
+Affected Shoots will remain in `Pending` state if the mentioned scheduler is not present in the landscape.
+
 ## `spec.seedName` Field in the `Shoot` Specification
+
 Similar to the `.spec.nodeName` field in `Pod`s, the `Shoot` specification has an optional `.spec.seedName` field. If this field is set on creation, the shoot will be scheduled to this seed. However, this field can only be set by users having RBAC for the `shoots/binding` subresource. If this field is not set, the `scheduler` will assign a suitable seed automatically and populate this field with the seed name.
 
 ## `seedSelector` Field in the `Shoot` Specification
@@ -116,4 +123,4 @@ In case the scheduler fails to find a suitable seed, the operation is being retr
 
 ## Current Limitation / Future Plans
 
-- Azure unfortunately has a geographically non-hierarchical naming pattern and does not start with the continent. This is the reason why we will exchange the implementation of the `MinimalDistance` strategy with a more suitable one in the future.
+- Azure unfortunately has a geographically non-hierarchical naming pattern and does not start with the continent. This is the reason why we will exchange the implementation of the `MinimalDistance` strategy with a more suitable one in the future.

example/90-shoot.yaml

@@ -8,6 +8,7 @@ spec:
   cloudProfileName: cloudprofile1
   region: europe-central-1
   purpose: evaluation # {testing,development,production,infrastructure}, "infrastructure" purpose only usable for shoots in garden namespace
+# schedulerName: default-scheduler
   provider:
     type: <some-provider-name> # {aws,azure,gcp,...}
     infrastructureConfig:

example/provider-local/managedseeds/shoot-managedseed.yaml

@@ -7,7 +7,6 @@ metadata:
     shoot.gardener.cloud/infrastructure-cleanup-wait-period-seconds: "0"
     shoot.gardener.cloud/cloud-config-execution-max-delay-seconds: "0"
 spec:
-  seedName: local
   cloudProfileName: local
   secretBindingName: local
   region: local
@@ -26,7 +25,6 @@ spec:
       maxSurge: 1
       maxUnavailable: 0
   kubernetes:
-    version: 1.24.8
     kubelet:
       serializeImagePulls: false
       registryPullQPS: 10

example/provider-local/shoot-workerless.yaml

@@ -4,7 +4,6 @@ metadata:
   name: local-wl
   namespace: garden-local
 spec:
-  seedName: local
   cloudProfileName: local
   region: local
   provider:

example/provider-local/shoot.yaml

@@ -7,7 +7,6 @@ metadata:
     shoot.gardener.cloud/infrastructure-cleanup-wait-period-seconds: "0"
     shoot.gardener.cloud/cloud-config-execution-max-delay-seconds: "0"
 spec:
-  seedName: local
   cloudProfileName: local
   secretBindingName: local # dummy, doesn't contain any credentials
   region: local

pkg/apis/core/types_shoot.go

@@ -106,6 +106,10 @@ type ShootSpec struct {
 	SystemComponents *SystemComponents
 	// ControlPlane contains general settings for the control plane of the shoot.
 	ControlPlane *ControlPlane
+	// SchedulerName is the name of the responsible scheduler which schedules the shoot.
+	// If not specified, the default scheduler takes over.
+	// This field is immutable.
+	SchedulerName *string
 }
 
 // GetProviderType gets the type of the provider.

pkg/apis/core/v1beta1/constants/types_constants.go

@@ -565,6 +565,9 @@ const (
 	// DefaultIngressGatewayAppLabelValue is the ingress gateway value for the app label.
 	DefaultIngressGatewayAppLabelValue = "istio-ingressgateway"
 
+	// DefaultSchedulerName is the name of the default scheduler.
+	DefaultSchedulerName = "default-scheduler"
+
 	// AnnotationManagedSeedAPIServer is a constant for an annotation on a Shoot resource containing the API server settings for a managed seed.
 	AnnotationManagedSeedAPIServer = "shoot.gardener.cloud/managed-seed-api-server"
 	// AnnotationShootIgnoreAlerts is the key for an annotation of a Shoot cluster whose value indicates

pkg/apis/core/v1beta1/defaults.go

@@ -258,6 +258,10 @@ func SetDefaults_Shoot(obj *Shoot) {
 			obj.Spec.SystemComponents.CoreDNS.Autoscaling.Mode = CoreDNSAutoscalingModeHorizontal
 		}
 	}
+
+	if obj.Spec.SchedulerName == nil {
+		obj.Spec.SchedulerName = pointer.String(v1beta1constants.DefaultSchedulerName)
+	}
 }
 
 // SetDefaults_KubeAPIServerConfig sets default values for KubeAPIServerConfig objects.

pkg/apis/core/v1beta1/defaults_test.go

@@ -313,6 +313,22 @@ var _ = Describe("Defaults", func() {
 			Expect(obj.Spec.Kubernetes.Kubelet.SerializeImagePulls).To(PointTo(BeFalse()))
 		})
 
+		It("should default schedulerName", func() {
+			obj.Spec.SchedulerName = nil
+
+			SetObjectDefaults_Shoot(obj)
+
+			Expect(obj.Spec.SchedulerName).To(PointTo(Equal("default-scheduler")))
+		})
+
+		It("should not default schedulerName", func() {
+			obj.Spec.SchedulerName = pointer.String("foo-scheduler")
+
+			SetObjectDefaults_Shoot(obj)
+
+			Expect(obj.Spec.SchedulerName).To(PointTo(Equal("foo-scheduler")))
+		})
+
 		Context("default kubeReserved", func() {
 			var (
 				defaultKubeReservedMemory = resource.MustParse("1Gi")