feat: Implement Issue #1779: add --canary-min-replicas command-line flag

cmd/rollouts-controller/main.go

@@ -60,6 +60,7 @@ func newCommand() *cobra.Command {
 		analysisThreads      int
 		serviceThreads       int
 		ingressThreads       int
+		canaryMinReplicas    int32
 		istioVersion         string
 		trafficSplitVersion  string
 		ambassadorVersion    string
@@ -95,6 +96,7 @@ func newCommand() *cobra.Command {
 			defaults.SetAmbassadorAPIVersion(ambassadorVersion)
 			defaults.SetSMIAPIVersion(trafficSplitVersion)
 			defaults.SetAppMeshCRDVersion(appmeshCRDVersion)
+			defaults.SetDefaultCanaryMinReplicas(canaryMinReplicas)
 
 			config, err := clientConfig.ClientConfig()
 			checkError(err)
@@ -225,6 +227,7 @@ func newCommand() *cobra.Command {
 	command.Flags().IntVar(&analysisThreads, "analysis-threads", controller.DefaultAnalysisThreads, "Set the number of worker threads for the Experiment controller")
 	command.Flags().IntVar(&serviceThreads, "service-threads", controller.DefaultServiceThreads, "Set the number of worker threads for the Service controller")
 	command.Flags().IntVar(&ingressThreads, "ingress-threads", controller.DefaultIngressThreads, "Set the number of worker threads for the Ingress controller")
+	command.Flags().Int32Var(&canaryMinReplicas, "canary-min-replicas", defaults.DefaultCanaryMinReplicas, "Set the minimum number of replicas for Canary ReplicaSets")
 	command.Flags().StringVar(&istioVersion, "istio-api-version", defaults.DefaultIstioVersion, "Set the default Istio apiVersion that controller should look when manipulating VirtualServices.")
 	command.Flags().StringVar(&ambassadorVersion, "ambassador-api-version", defaults.DefaultAmbassadorVersion, "Set the Ambassador apiVersion that controller should look when manipulating Ambassador Mappings.")
 	command.Flags().StringVar(&trafficSplitVersion, "traffic-split-api-version", defaults.DefaultSMITrafficSplitVersion, "Set the default TrafficSplit apiVersion that controller uses when creating TrafficSplits.")

utils/defaults/defaults.go

@@ -45,6 +45,8 @@ const (
 	// DefaultMetricCleanupDelay is the default time to delay metrics removal upon object removal, gives time for metrics
 	// to be collected
 	DefaultMetricCleanupDelay = int32(65)
+	// DefaultCanaryMinReplicas is the minimum pods in a Replicaset for Canary traffic routing
+	DefaultCanaryMinReplicas = int32(1)
 )
 
 const (
@@ -66,6 +68,7 @@ var (
 	targetGroupBindingAPIVersion = DefaultTargetGroupBindingAPIVersion
 	appmeshCRDVersion            = DefaultAppMeshCRDVersion
 	defaultMetricCleanupDelay    = DefaultMetricCleanupDelay
+	defaultCanaryMinReplicas     = DefaultCanaryMinReplicas
 )
 
 const (
@@ -318,3 +321,13 @@ func GetMetricCleanupDelaySeconds() time.Duration {
 func SetMetricCleanupDelaySeconds(seconds int32) {
 	defaultMetricCleanupDelay = seconds
 }
+
+// GetDefaultCanaryMinReplicas returns the minimum pods in a Replicaset for Canary traffic routing
+func GetDefaultCanaryMinReplicas() int32 {
+	return defaultCanaryMinReplicas
+}
+
+// SetDefaultCanaryMinReplicas sets the minimum pods in a Replicaset for Canary traffic routing
+func SetDefaultCanaryMinReplicas(replicas int32) {
+	defaultCanaryMinReplicas = replicas
+}

utils/replicaset/canary.go

@@ -25,6 +25,13 @@ func allDesiredAreCreated(rs *appsv1.ReplicaSet, desired int32) bool {
 	return rs != nil && desired == *rs.Spec.Replicas && desired == rs.Status.Replicas
 }
 
+func checkMinPods(rollout *v1alpha1.Rollout, replicas int32) int32 {
+	if replicas > 0 && rollout.Spec.Replicas != nil && *rollout.Spec.Replicas >= defaults.GetDefaultCanaryMinReplicas() {
+		replicas = max(replicas, defaults.GetDefaultCanaryMinReplicas())
+	}
+	return replicas
+}
+
 func AtDesiredReplicaCountsForCanary(ro *v1alpha1.Rollout, newRS, stableRS *appsv1.ReplicaSet, olderRSs []*appsv1.ReplicaSet, weights *v1alpha1.TrafficWeights) bool {
 	var desiredNewRSReplicaCount, desiredStableRSReplicaCount int32
 	if ro.Spec.Strategy.Canary.TrafficRouting == nil {
@@ -142,7 +149,7 @@ func CalculateReplicaCountsForBasicCanary(rollout *v1alpha1.Rollout, newRS *apps
 	if GetReplicaCountForReplicaSets(oldRSs) > 0 {
 		// If any older ReplicaSets exist, we should scale those down first, before even considering
 		// scaling down the newRS or stableRS
-		return newRSReplicaCount, stableRSReplicaCount
+		return checkMinPods(rollout, newRSReplicaCount), checkMinPods(rollout, stableRSReplicaCount)
 	}
 
 	minAvailableReplicaCount := rolloutSpecReplica - MaxUnavailable(rollout)
@@ -154,7 +161,7 @@ func CalculateReplicaCountsForBasicCanary(rollout *v1alpha1.Rollout, newRS *apps
 	replicasToScaleDown := GetReplicasForScaleDown(newRS, !isIncreasing) + GetReplicasForScaleDown(stableRS, isIncreasing)
 	if replicasToScaleDown <= minAvailableReplicaCount {
 		// Cannot scale down stableRS or newRS without going below min available replica count
-		return newRSReplicaCount, stableRSReplicaCount
+		return checkMinPods(rollout, newRSReplicaCount), checkMinPods(rollout, stableRSReplicaCount)
 	}
 
 	scaleDownCount := replicasToScaleDown - minAvailableReplicaCount
@@ -167,7 +174,7 @@ func CalculateReplicaCountsForBasicCanary(rollout *v1alpha1.Rollout, newRS *apps
 		stableRSReplicaCount = calculateScaleDownReplicaCount(stableRS, desiredStableRSReplicaCount, scaleDownCount, stableRSReplicaCount)
 		stableRSReplicaCount, newRSReplicaCount = adjustReplicaWithinLimits(stableRS, newRS, stableRSReplicaCount, newRSReplicaCount, maxReplicaCountAllowed, minAvailableReplicaCount)
 	}
-	return newRSReplicaCount, stableRSReplicaCount
+	return checkMinPods(rollout, newRSReplicaCount), checkMinPods(rollout, stableRSReplicaCount)
 }
 
 // approximateWeightedCanaryStableReplicaCounts approximates the desired canary weight and returns
@@ -329,7 +336,7 @@ func CalculateReplicaCountsForTrafficRoutedCanary(rollout *v1alpha1.Rollout, wei
 	if !rollout.Spec.Strategy.Canary.DynamicStableScale {
 		// Not using dynamic stable scaling. Stable should be left fully scaled (100%), and canary
 		// will be calculated from setWeight
-		return canaryCount, rolloutSpecReplica
+		return checkMinPods(rollout, canaryCount), rolloutSpecReplica
 	}
 
 	// When using dynamic stable scaling, the stable replica count is calculated from the higher of:
@@ -354,7 +361,7 @@ func CalculateReplicaCountsForTrafficRoutedCanary(rollout *v1alpha1.Rollout, wei
 			canaryCount = max(trafficWeightReplicaCount, canaryCount)
 		}
 	}
-	return canaryCount, stableCount
+	return checkMinPods(rollout, canaryCount), checkMinPods(rollout, stableCount)
 }
 
 // trafficWeightToReplicas returns the appropriate replicas given the full spec.replicas and a weight

utils/replicaset/canary_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/argoproj/argo-rollouts/utils/defaults"
 	"github.com/stretchr/testify/assert"
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
@@ -798,6 +799,39 @@ func TestCalculateReplicaCountsForCanaryTrafficRouting(t *testing.T) {
 	assert.Equal(t, int32(10), stableRSReplicaCount)
 }
 
+func TestCalculateReplicaCountsForCanaryWithMinPods(t *testing.T) {
+	minPods := defaults.GetDefaultCanaryMinReplicas() // Save initial value
+	rollout := newRollout(10, 1, intstr.FromInt(0), intstr.FromInt(1), "canary", "stable", nil, nil)
+
+	// first test Basic Canary without minPods
+	stableRS := newRS("stable", 10, 0)
+	newRS := newRS("canary", 10, 0)
+	newRSReplicaCount, stableRSReplicaCount := CalculateReplicaCountsForBasicCanary(rollout, newRS, stableRS, nil)
+	assert.Equal(t, int32(9), newRSReplicaCount)
+	assert.Equal(t, int32(1), stableRSReplicaCount)
+
+	// Now test Basic Canary with minPods
+	defaults.SetDefaultCanaryMinReplicas(int32(2))
+	newRSReplicaCount, stableRSReplicaCount = CalculateReplicaCountsForBasicCanary(rollout, newRS, stableRS, nil)
+	assert.Equal(t, int32(9), newRSReplicaCount)
+	assert.Equal(t, int32(2), stableRSReplicaCount)
+
+	// Now test TrafficRouted Canary
+	rollout.Spec.Strategy.Canary.TrafficRouting = &v1alpha1.RolloutTrafficRouting{}
+	newRSReplicaCount, stableRSReplicaCount = CalculateReplicaCountsForTrafficRoutedCanary(rollout, rollout.Status.Canary.Weights)
+	assert.Equal(t, int32(2), newRSReplicaCount)
+	assert.Equal(t, int32(10), stableRSReplicaCount)
+
+	// Test that we don't use minPods when desired replicas < minPods
+	rollout = newRollout(1, 1, intstr.FromInt(0), intstr.FromInt(1), "canary", "stable", nil, nil)
+	rollout.Spec.Strategy.Canary.TrafficRouting = &v1alpha1.RolloutTrafficRouting{}
+	newRSReplicaCount, stableRSReplicaCount = CalculateReplicaCountsForTrafficRoutedCanary(rollout, rollout.Status.Canary.Weights)
+	assert.Equal(t, int32(1), newRSReplicaCount)
+	assert.Equal(t, int32(1), stableRSReplicaCount)
+
+	defaults.SetDefaultCanaryMinReplicas(minPods) // Restore initial value
+}
+
 func TestCalculateReplicaCountsForCanaryTrafficRoutingDynamicScale(t *testing.T) {
 	{
 		// verify we scale down stable