✨ Add support for in-place upgrades in MachineDeployments

api/v1beta1/machinedeployment_types.go

@@ -35,6 +35,9 @@ const (
 	// i.e. gradually scale down the old MachineSet and scale up the new one.
 	RollingUpdateMachineDeploymentStrategyType MachineDeploymentStrategyType = "RollingUpdate"
 
+	// InPlaceMachineDeploymentStrategyType upgrades the machines within the same MachineSet without rolling out any new nodes.
+	InPlaceMachineDeploymentStrategyType MachineDeploymentStrategyType = "InPlace"
+
 	// OnDeleteMachineDeploymentStrategyType replaces old MachineSets when the deletion of the associated machines are completed.
 	OnDeleteMachineDeploymentStrategyType MachineDeploymentStrategyType = "OnDelete"
 
@@ -54,6 +57,12 @@ const (
 	// proportions in case the deployment has surge replicas.
 	MaxReplicasAnnotation = "machinedeployment.clusters.x-k8s.io/max-replicas"
 
+	// MachineDeploymentInPlaceUpgradeAnnotation is used to denote that the MachineDeployment needs to be in-place upgraded by an external entity.
+	// This annotation will be added to the MD object when `strategy.type` is set to `InPlace`.
+	// The external upgrader entity should watch for the annotation and trigger an upgrade when it's added.
+	// Once the upgrade is complete, the external upgrade implementer is also responsible for removing this annotation.
+	MachineDeploymentInPlaceUpgradeAnnotation = "machinedeployment.clusters.x-k8s.io/in-place-upgrade-needed"
+
 	// MachineDeploymentUniqueLabel is used to uniquely identify the Machines of a MachineSet.
 	// The MachineDeployment controller will set this label on a MachineSet when it is created.
 	// The label is also applied to the Machines of the MachineSet and used in the MachineSet selector.
@@ -154,7 +163,7 @@ type MachineDeploymentSpec struct {
 type MachineDeploymentStrategy struct {
 	// Type of deployment. Allowed values are RollingUpdate and OnDelete.
 	// The default is RollingUpdate.
-	// +kubebuilder:validation:Enum=RollingUpdate;OnDelete
+	// +kubebuilder:validation:Enum=RollingUpdate;OnDelete;InPlace
 	// +optional
 	Type MachineDeploymentStrategyType `json:"type,omitempty"`
 

internal/controllers/machinedeployment/machinedeployment_controller.go

@@ -278,6 +278,10 @@ func (r *Reconciler) reconcile(ctx context.Context, cluster *clusterv1.Cluster,
 		return r.rolloutRolling(ctx, md, msList)
 	}
 
+	if md.Spec.Strategy.Type == clusterv1.InPlaceMachineDeploymentStrategyType {
+		return r.rolloutInPlace(ctx, md, msList)
+	}
+
 	if md.Spec.Strategy.Type == clusterv1.OnDeleteMachineDeploymentStrategyType {
 		return r.rolloutOnDelete(ctx, md, msList)
 	}

internal/controllers/machinedeployment/machinedeployment_inplace.go

@@ -0,0 +1,44 @@
+package machinedeployment
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+	kerrors "k8s.io/apimachinery/pkg/util/errors"
+	ctrl "sigs.k8s.io/controller-runtime"
+
+	clusterv1 "sigs.k8s.io/cluster-api/api/v1beta1"
+	"sigs.k8s.io/cluster-api/util/annotations"
+)
+
+func (r *Reconciler) rolloutInPlace(ctx context.Context, md *clusterv1.MachineDeployment, msList []*clusterv1.MachineSet) (reterr error) {
+	log := ctrl.LoggerFrom(ctx)
+
+	// For in-place upgrade, we shouldn't try to create a new MachineSet as that would trigger a rollout.
+	// Instead, we should try to get latest MachineSet that matches the MachineDeployment.Spec.Template/
+	// If no such MachineSet exists yet, this means the MachineSet hasn't been in-place upgraded yet.
+	// The external in-place upgrade implementer is responsible for updating the latest MachineSet's template
+	// after in-place upgrade of all worker nodes belonging to the MD is complete.
+	// Once the MachineSet is updated, this function will return the latest MachineSet that matches the
+	// MachineDeployment template and thus we can deduce that the in-place upgrade is complete.
+	newMachineSet, oldMachineSets, err := r.getAllMachineSetsAndSyncRevision(ctx, md, msList, false)
+	if err != nil {
+		return err
+	}
+
+	defer func() {
+		allMSs := append(oldMachineSets, newMachineSet)
+
+		// Always attempt to sync the status
+		err := r.syncDeploymentStatus(allMSs, newMachineSet, md)
+		reterr = kerrors.NewAggregate([]error{reterr, err})
+	}()
+
+	if newMachineSet == nil {
+		log.Info("Changes detected, InPlace upgrade strategy detected, adding the annotation")
+		annotations.AddAnnotations(md, map[string]string{clusterv1.MachineDeploymentInPlaceUpgradeAnnotation: "true"})
+		return errors.New("new MachineSet not found. This most likely means that the in-place upgrade hasn't finished yet")
+	}
+
+	return r.sync(ctx, md, msList)
+}

internal/controllers/machinedeployment/machinedeployment_inplace_test.go

@@ -0,0 +1,110 @@
+package machinedeployment
+
+import (
+	"testing"
+
+	. "github.com/onsi/gomega"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/tools/record"
+	"k8s.io/utils/pointer"
+	clusterv1 "sigs.k8s.io/cluster-api/api/v1beta1"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+)
+
+const (
+	mdName     = "my-md"
+	msName     = "my-ms"
+	version128 = "v1.28.0"
+	version129 = "v1.29.0"
+)
+
+func getMachineDeployment(name string, version string, replicas int32) *clusterv1.MachineDeployment {
+	return &clusterv1.MachineDeployment{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: name,
+		},
+		Spec: clusterv1.MachineDeploymentSpec{
+			Strategy: &clusterv1.MachineDeploymentStrategy{
+				Type: clusterv1.InPlaceMachineDeploymentStrategyType,
+			},
+			Replicas: pointer.Int32(replicas),
+			Template: clusterv1.MachineTemplateSpec{
+				Spec: clusterv1.MachineSpec{
+					ClusterName: "my-cluster",
+					Version:     pointer.String(version),
+				},
+			},
+		},
+	}
+}
+
+func getMachineSet(name string, version string, replicas int32) *clusterv1.MachineSet {
+	return &clusterv1.MachineSet{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: name,
+		},
+		Spec: clusterv1.MachineSetSpec{
+			Replicas: pointer.Int32(replicas),
+			Template: clusterv1.MachineTemplateSpec{
+				Spec: clusterv1.MachineSpec{
+					ClusterName: "my-cluster",
+					Version:     pointer.String(version),
+				},
+			},
+		},
+	}
+}
+
+func TestRolloutInPlace(t *testing.T) {
+	testCases := []struct {
+		name               string
+		machineDeployment  *clusterv1.MachineDeployment
+		msList             []*clusterv1.MachineSet
+		annotationExpected bool
+		expectErr          bool
+	}{
+		{
+			name:               "MD template matches MS template",
+			machineDeployment:  getMachineDeployment(mdName, version128, 2),
+			msList:             []*clusterv1.MachineSet{getMachineSet(msName, version128, 2)},
+			annotationExpected: false,
+			expectErr:          false,
+		},
+		{
+			name:               "MD template doesn't MS template",
+			machineDeployment:  getMachineDeployment(mdName, version128, 2),
+			msList:             []*clusterv1.MachineSet{getMachineSet(msName, version129, 2)},
+			annotationExpected: true,
+			expectErr:          true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			g := NewWithT(t)
+
+			resources := []client.Object{
+				tc.machineDeployment,
+			}
+
+			for key := range tc.msList {
+				resources = append(resources, tc.msList[key])
+			}
+
+			r := &Reconciler{
+				Client:   fake.NewClientBuilder().WithObjects(resources...).Build(),
+				recorder: record.NewFakeRecorder(32),
+			}
+
+			err := r.rolloutInPlace(ctx, tc.machineDeployment, tc.msList)
+			if tc.expectErr {
+				g.Expect(err).To(HaveOccurred())
+			}
+
+			_, ok := tc.machineDeployment.Annotations[clusterv1.MachineDeploymentInPlaceUpgradeAnnotation]
+			g.Expect(ok).To(Equal(tc.annotationExpected))
+		})
+	}
+
+}

internal/controllers/machinedeployment/mdutil/util.go

@@ -563,6 +563,8 @@ func NewMSNewReplicas(deployment *clusterv1.MachineDeployment, allMSs []*cluster
 		// the desired number of replicas in the MachineDeployment
 		scaleUpCount := *(deployment.Spec.Replicas) - currentMachineCount
 		return newMSReplicas + scaleUpCount, nil
+	case clusterv1.InPlaceMachineDeploymentStrategyType:
+		return 0, nil
 	default:
 		return 0, fmt.Errorf("failed to compute replicas: deployment strategy %v isn't supported", deployment.Spec.Strategy.Type)
 	}