feat: automatically scale down Deployment after migrating to Rollout

docs/features/specification.md

@@ -33,6 +33,13 @@ spec:
     apiVersion: apps/v1
     kind: Deployment
     name: rollout-ref-deployment
+    # Specifies if the workload (Deployment) is scaled down after migrating to Rollout.
+    # The possible options are:
+    # "never": the Deployment is not scaled down
+    # "onsuccess": the Deployment is scaled down after the Rollout becomes healthy
+    # "progressively": as the Rollout is scaled up the Deployment is scaled down
+    # If the Rollout fails the Deployment will be scaled back up.
+    scaleDown: never|onsuccess|progressively
 
   # Template describes the pods that will be created. Same as deployment.
   # If used, then do not use Rollout workloadRef property. 

docs/migrating.md

@@ -54,7 +54,11 @@ Instead of removing Deployment you can scale it down to zero and reference it fr
 
 1. Create a Rollout resource.
 1. Reference an existing Deployment using `workloadRef` field.
-1. Scale-down an existing Deployment by changing `replicas` field of an existing Deployment to zero.
+1. In the `workloadRef` field set the `scaleDown` attribute, which specifies how the Deployment should be scaled down. There are three options available:
+* "never": the Deployment is not scaled down
+* "onsuccess": the Deployment is scaled down after the Rollout becomes healthy
+* "progressively": as the Rollout is scaled up the Deployment is scaled down.
+Alternatively, manually scale down an existing Deployment by changing replicas field of an existing Deployment to zero.
 1. To perform an update, the change should be made to the Pod template field of the Deployment.
 
 Below is an example of a Rollout resource referencing a Deployment.
@@ -73,6 +77,7 @@ spec:
     apiVersion: apps/v1
     kind: Deployment
     name: rollout-ref-deployment
+    scaleDown: onsuccess
   strategy:
     canary:
       steps:

manifests/crds/rollout-crd.yaml

@@ -3330,6 +3330,8 @@ spec:
                     type: string
                   name:
                     type: string
+                  scaleDown:
+                    type: string
                 type: object
             type: object
           status:

manifests/install.yaml

@@ -14920,6 +14920,8 @@ spec:
                     type: string
                   name:
                     type: string
+                  scaleDown:
+                    type: string
                 type: object
             type: object
           status:

pkg/apiclient/rollout/rollout.swagger.json

@@ -1695,6 +1695,10 @@
         "name": {
           "type": "string",
           "title": "Name of the referent"
+        },
+        "scaleDown": {
+          "type": "string",
+          "title": "Automatically scale down deployment"
         }
       },
       "title": "ObjectRef holds a references to the Kubernetes object"

pkg/apis/rollouts/v1alpha1/types.go

@@ -137,6 +137,8 @@ type ObjectRef struct {
 	Kind string `json:"kind,omitempty" protobuf:"bytes,2,opt,name=kind"`
 	// Name of the referent
 	Name string `json:"name,omitempty" protobuf:"bytes,3,opt,name=name"`
+	// Automatically scale down deployment
+	ScaleDown string `json:"scaleDown,omitempty" protobuf:"bytes,4,opt,name=scaleDown"`
 }
 
 const (
@@ -1081,3 +1083,9 @@ type RolloutList struct {
 type RollbackWindowSpec struct {
 	Revisions int32 `json:"revisions,omitempty" protobuf:"varint,1,opt,name=revisions"`
 }
+
+const (
+	ScaleDownNever         string = "never"
+	ScaleDownOnSuccess     string = "onsuccess"
+	ScaleDownProgressively string = "progressively"
+)

rollout/replicaset.go

@@ -172,6 +172,22 @@
 	}
 
 	scaled, _, err := c.scaleReplicaSetAndRecordEvent(c.newRS, newReplicasCount)
+
+	if err != nil {
+		return scaled, err
+	}
+
+	revision, _ := replicasetutil.Revision(c.newRS)
+
+	if revision == 1 && c.rollout.Spec.WorkloadRef != nil && c.rollout.Spec.WorkloadRef.ScaleDown == v1alpha1.ScaleDownProgressively {
+		oldScale := defaults.GetReplicasOrDefault(c.newRS.Spec.Replicas)
+		// scale down the deployment when the rollout has ready replicas or scale up the deployment if rollout fails
+		if c.rollout.Spec.Replicas != nil && (c.rollout.Status.ReadyReplicas > 0 || oldScale > newReplicasCount) {
+			targetScale := *c.rollout.Spec.Replicas - c.rollout.Status.ReadyReplicas
+			err = c.scaleDeployment(&targetScale)
+		}
+	}
+
 	return scaled, err
 }
 

rollout/replicaset_test.go

@@ -1,6 +1,7 @@
 package rollout
 
 import (
+	"context"
 	"fmt"
 	"strconv"
 	"testing"
@@ -574,3 +575,70 @@ func TestIsReplicaSetReferenced(t *testing.T) {
 		})
 	}
 }
+
+func TestScaleDownProgressively(t *testing.T) {
+
+	tests := []struct {
+		name                       string
+		deploymentReplicas         int32
+		newRSReplicas              int
+		newRSRevision              string
+		rolloutReplicas            int32
+		rolloutReadyReplicas       int32
+		abortScaleDownDelaySeconds int32
+		expectedDeploymentReplicas int32
+	}{
+		{
+			name:                       "Scale down deployment",
+			deploymentReplicas:         5,
+			newRSReplicas:              5,
+			newRSRevision:              "1",
+			rolloutReplicas:            5,
+			rolloutReadyReplicas:       3,
+			abortScaleDownDelaySeconds: 0,
+			expectedDeploymentReplicas: 2,
+		},
+		{
+			name:                       "Scale up deployment",
+			deploymentReplicas:         0,
+			newRSReplicas:              5,
+			newRSRevision:              "1",
+			rolloutReplicas:            5,
+			rolloutReadyReplicas:       1,
+			abortScaleDownDelaySeconds: 0,
+			expectedDeploymentReplicas: 4,
+		},
+		{
+			name:                       "Do not scale deployment",
+			deploymentReplicas:         5,
+			newRSReplicas:              5,
+			newRSRevision:              "2",
+			rolloutReplicas:            5,
+			rolloutReadyReplicas:       3,
+			abortScaleDownDelaySeconds: 0,
+			expectedDeploymentReplicas: 5,
+		},
+	}
+
+	for _, test := range tests {
+		ctx := createScaleDownRolloutContext(v1alpha1.ScaleDownProgressively, test.deploymentReplicas, true, nil)
+		ctx.rollout.Spec.Strategy = v1alpha1.RolloutStrategy{
+			BlueGreen: &v1alpha1.BlueGreenStrategy{
+				AbortScaleDownDelaySeconds: &test.abortScaleDownDelaySeconds,
+			},
+		}
+		ctx.newRS = rs("foo-v2", test.newRSReplicas, nil, noTimestamp, nil)
+		ctx.newRS.ObjectMeta.Annotations[annotations.RevisionAnnotation] = test.newRSRevision
+		ctx.pauseContext.removeAbort = true
+		ctx.rollout.Spec.Replicas = &test.rolloutReplicas
+		ctx.rollout.Status.ReadyReplicas = test.rolloutReadyReplicas
+
+		_, err := ctx.reconcileNewReplicaSet()
+		assert.Nil(t, err)
+		k8sfakeClient := ctx.kubeclientset.(*k8sfake.Clientset)
+		updatedDeployment, err := k8sfakeClient.AppsV1().Deployments("default").Get(context.TODO(), "workload-test", metav1.GetOptions{})
+		assert.Nil(t, err)
+		assert.Equal(t, test.expectedDeploymentReplicas, *updatedDeployment.Spec.Replicas)
+
+	}
+}

rollout/scale_utils.go

@@ -0,0 +1,36 @@
+package rollout
+
+import (
+	"context"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+func (c *rolloutContext) scaleDeployment(targetScale *int32) error {
+	deploymentName := c.rollout.Spec.WorkloadRef.Name
+	namespace := c.rollout.Namespace
+	deployment, err := c.kubeclientset.AppsV1().Deployments(namespace).Get(context.TODO(), deploymentName, metav1.GetOptions{})
+	if err != nil {
+		c.log.Warnf("Failed to fetch deployment %s: %s", deploymentName, err.Error())
+		return err
+	}
+
+	var newReplicasCount int32
+	if *targetScale < 0 {
+		newReplicasCount = 0
+	} else {
+		newReplicasCount = *targetScale
+	}
+	if newReplicasCount == *deployment.Spec.Replicas {
+		return nil
+	}
+	c.log.Infof("Scaling deployment %s to %d replicas", deploymentName, newReplicasCount)
+	*deployment.Spec.Replicas = newReplicasCount
+
+	_, err = c.kubeclientset.AppsV1().Deployments(namespace).Update(context.TODO(), deployment, metav1.UpdateOptions{})
+	if err != nil {
+		c.log.Warnf("Failed to update deployment %s: %s", deploymentName, err.Error())
+		return err
+	}
+	return nil
+}