fix: only enable dynamic cluster sharding feature explicitly

cmd/argocd-application-controller/commands/argocd_application_controller.go

@@ -45,28 +45,29 @@ const (
 
 func NewCommand() *cobra.Command {
 	var (
-		clientConfig             clientcmd.ClientConfig
-		appResyncPeriod          int64
-		appHardResyncPeriod      int64
-		repoServerAddress        string
-		repoServerTimeoutSeconds int
-		selfHealTimeoutSeconds   int
-		statusProcessors         int
-		operationProcessors      int
-		glogLevel                int
-		metricsPort              int
-		metricsCacheExpiration   time.Duration
-		metricsAplicationLabels  []string
-		kubectlParallelismLimit  int64
-		cacheSource              func() (*appstatecache.Cache, error)
-		redisClient              *redis.Client
-		repoServerPlaintext      bool
-		repoServerStrictTLS      bool
-		otlpAddress              string
-		otlpAttrs                []string
-		applicationNamespaces    []string
-		persistResourceHealth    bool
-		shardingAlgorithm        string
+		clientConfig                     clientcmd.ClientConfig
+		appResyncPeriod                  int64
+		appHardResyncPeriod              int64
+		repoServerAddress                string
+		repoServerTimeoutSeconds         int
+		selfHealTimeoutSeconds           int
+		statusProcessors                 int
+		operationProcessors              int
+		glogLevel                        int
+		metricsPort                      int
+		metricsCacheExpiration           time.Duration
+		metricsAplicationLabels          []string
+		kubectlParallelismLimit          int64
+		cacheSource                      func() (*appstatecache.Cache, error)
+		redisClient                      *redis.Client
+		repoServerPlaintext              bool
+		repoServerStrictTLS              bool
+		otlpAddress                      string
+		otlpAttrs                        []string
+		applicationNamespaces            []string
+		persistResourceHealth            bool
+		shardingAlgorithm                string
+		enableDynamicClusterDistribution bool
 	)
 	var command = cobra.Command{
 		Use:               cliName,
@@ -139,7 +140,7 @@ func NewCommand() *cobra.Command {
 				appController.InvalidateProjectsCache()
 			}))
 			kubectl := kubeutil.NewKubectl()
-			clusterFilter := getClusterFilter(kubeClient, settingsMgr, shardingAlgorithm)
+			clusterFilter := getClusterFilter(kubeClient, settingsMgr, shardingAlgorithm, enableDynamicClusterDistribution)
 			errors.CheckError(err)
 			appController, err = controller.NewApplicationController(
 				namespace,
@@ -204,13 +205,14 @@ func NewCommand() *cobra.Command {
 	command.Flags().StringSliceVar(&applicationNamespaces, "application-namespaces", env.StringsFromEnv("ARGOCD_APPLICATION_NAMESPACES", []string{}, ","), "List of additional namespaces that applications are allowed to be reconciled from")
 	command.Flags().BoolVar(&persistResourceHealth, "persist-resource-health", env.ParseBoolFromEnv("ARGOCD_APPLICATION_CONTROLLER_PERSIST_RESOURCE_HEALTH", true), "Enables storing the managed resources health in the Application CRD")
 	command.Flags().StringVar(&shardingAlgorithm, "sharding-method", env.StringFromEnv(common.EnvControllerShardingAlgorithm, common.DefaultShardingAlgorithm), "Enables choice of sharding method. Supported sharding methods are : [legacy, round-robin] ")
+	command.Flags().StringVar(&enableDynamicClusterDistribution, "dynamic-cluster-distribution-enabled", env.ParseBoolFromEnv(common.EnvEnableDynamicClusterDistribution, false), "Enables dynamic cluster distribution.")
 	cacheSource = appstatecache.AddCacheFlagsToCmd(&command, func(client *redis.Client) {
 		redisClient = client
 	})
 	return &command
 }
 
-func getClusterFilter(kubeClient *kubernetes.Clientset, settingsMgr *settings.SettingsManager, shardingAlgorithm string) sharding.ClusterFilterFunction {
+func getClusterFilter(kubeClient *kubernetes.Clientset, settingsMgr *settings.SettingsManager, shardingAlgorithm string, enableDynamicClusterDistribution bool) sharding.ClusterFilterFunction {
 
 	var replicas int
 	shard := env.ParseNumFromEnv(common.EnvControllerShard, -1, -math.MaxInt32, math.MaxInt32)
@@ -223,7 +225,7 @@ func getClusterFilter(kubeClient *kubernetes.Clientset, settingsMgr *settings.Se
 		appControllerDeployment = nil
 	}
 
-	if appControllerDeployment != nil && appControllerDeployment.Spec.Replicas != nil {
+	if enableDynamicClusterDistribution && appControllerDeployment != nil && appControllerDeployment.Spec.Replicas != nil {
 		replicas = int(*appControllerDeployment.Spec.Replicas)
 	} else {
 		replicas = env.ParseNumFromEnv(common.EnvControllerReplicas, 0, 0, math.MaxInt32)
@@ -233,7 +235,7 @@ func getClusterFilter(kubeClient *kubernetes.Clientset, settingsMgr *settings.Se
 	if replicas > 1 {
 		// check for shard mapping using configmap if application-controller is a deployment
 		// else use existing logic to infer shard from pod name if application-controller is a statefulset
-		if appControllerDeployment != nil {
+		if appControllerDeployment != nil && enableDynamicClusterDistribution {
 
 			var err error
 			// retry 3 times if we find a conflict while updating shard mapping configMap.

common/common.go

@@ -224,6 +224,8 @@ const (
 	EnvControllerShard = "ARGOCD_CONTROLLER_SHARD"
 	// EnvControllerShardingAlgorithm is the distribution sharding algorithm to be used: legacy or round-robin
 	EnvControllerShardingAlgorithm = "ARGOCD_CONTROLLER_SHARDING_ALGORITHM"
+	//EnvEnableDynamicClusterDistribution enables dynamic sharding (ALPHA)
+	EnvEnableDynamicClusterDistribution = "ARGOCD_ENABLE_DYNAMIC_CLUSTER_DISTRIBUTION"
 	// EnvEnableGRPCTimeHistogramEnv enables gRPC metrics collection
 	EnvEnableGRPCTimeHistogramEnv = "ARGOCD_ENABLE_GRPC_TIME_HISTOGRAM"
 	// EnvGithubAppCredsExpirationDuration controls the caching of Github app credentials. This value is in minutes (default: 60)

docs/operator-manual/dynamic-cluster-distribution.md

@@ -17,6 +17,8 @@ which does not require a restart of the application controller pods.
 
 ## Enabling Dynamic Distribution of Clusters
 
+This feature is disabled by default while it is in alpha. To enable it, you must set the environment `ARGOCD_ENABLE_DYNAMIC_CLUSTER_DISTRIBUTION` to true when running the Application Controller.
+
 In order to utilize the feature, the manifests `manifests/ha/base/controller-deployment/` can be applied as a Kustomize 
 overlay. This overlay sets the StatefulSet replicas to `0` and deploys the application controller as a Deployment. The
 dynamic distribution code automatically kicks in when the controller is deployed as a Deployment.