add reconcile-reources flag (#176)

The AWS Controllers for Kubernetes (ACK) service controllers currently initialize reconcilers for all supported resource kinds, regardless of operational needs, leading to unnecessary resource consumption and potential for conflicts. We propose introducing a --reconcile-resources flag that allows operators to specify which resource kinds should be actively reconciled, enabling more efficient resource utilization and operational control. When provided with a comma-separated list of resource kinds (e.g., "Queue,Topic"), the controller will only create reconcilers for those specific resources. This enhancement maintains backward compatibility by continuing to reconcile all resources when the flag is not specified.

Author: rushmash91

pkg/config/config.go

@@ -64,6 +64,7 @@ const (
 	flagReconcileDefaultMaxConcurrency  = "reconcile-default-max-concurrent-syncs"
 	flagReconcileResourceMaxConcurrency = "reconcile-resource-max-concurrent-syncs"
 	flagFeatureGates                    = "feature-gates"
+	flagReconcileResources              = "reconcile-resources"
 	envVarAWSRegion                     = "AWS_REGION"
 )
 
@@ -104,6 +105,7 @@ type Config struct {
 	ReconcileResourceResyncSeconds  []string
 	ReconcileDefaultMaxConcurrency  int
 	ReconcileResourceMaxConcurrency []string
+	ReconcileResources              string
 	// TODO(a-hilaly): migrate to k8s.io/component-base and implement a proper parser for feature gates.
 	FeatureGates    featuregate.FeatureGates
 	featureGatesRaw string
@@ -250,6 +252,11 @@ func (cfg *Config) BindFlags() {
 			"Valid keys are feature names and valid values are 'true' or 'false'."+
 			"Available features: "+strings.Join(featuregate.GetDefaultFeatureGates().GetFeatureNames(), ", "),
 	)
+	flag.StringVar(
+		&cfg.ReconcileResources, flagReconcileResources,
+		"",
+		"A comma-separated list of resource kinds to reconcile. If unspecified, all resources will be reconciled.",
+	)
 }
 
 // SetupLogger initializes the logger used in the service controller
@@ -389,6 +396,12 @@ func (cfg *Config) validateReconcileConfigResources(supportedGVKs []schema.Group
 			return fmt.Errorf("invalid value for flag '%s': %v", flagReconcileResourceMaxConcurrency, err)
 		}
 	}
+
+	// Also validate the resource filter settings
+	if err := cfg.validateReconcileResources(validResourceNames); err != nil {
+		return err
+	}
+
 	return nil
 }
 
@@ -564,3 +577,56 @@ func parseFeatureGates(featureGatesRaw string) (map[string]bool, error) {
 
 	return featureGatesMap, nil
 }
+
+// GetReconcileResources returns a slice of resource kinds that should be reconciled.
+func (cfg *Config) GetReconcileResources() ([]string, error) {
+	return parseReconcileResourcesString(cfg.ReconcileResources)
+}
+
+// parseReconcileResourcesString parses the reconcileResources flag and returns a slice
+// of resource kinds to reconcile.
+func parseReconcileResourcesString(resources string) ([]string, error) {
+	resources = strings.TrimSpace(resources)
+	if resources == "" {
+		return nil, nil
+	}
+
+	visited := make(map[string]bool)
+	resourceKinds := []string{}
+
+	for _, kind := range strings.Split(resources, ",") {
+		kind = strings.TrimSpace(kind)
+		if kind == "" {
+			return nil, fmt.Errorf("invalid resource kind: empty kind")
+		}
+		if _, ok := visited[kind]; ok {
+			return nil, fmt.Errorf("duplicate resource kind '%s'", kind)
+		}
+		visited[kind] = true
+		resourceKinds = append(resourceKinds, kind)
+	}
+	return resourceKinds, nil
+}
+
+// validateReconcileResources validates that the specified resource kinds are supported by the controller.
+func (cfg *Config) validateReconcileResources(validResourceNames []string) error {
+	resources, err := cfg.GetReconcileResources()
+	if err != nil {
+		return fmt.Errorf("invalid value for flag '%s': %v", flagReconcileResources, err)
+	}
+	if len(resources) == 0 {
+		return nil
+	}
+
+	for _, resource := range resources {
+		if !ackutil.InStrings(resource, validResourceNames) {
+			return fmt.Errorf(
+				"invalid value for flag '%s': resource kind '%s' is not supported by this controller. Valid resource kinds are: %s",
+				flagReconcileResources,
+				resource,
+				strings.Join(validResourceNames, ", "),
+			)
+		}
+	}
+	return nil
+}

pkg/runtime/service_controller.go

@@ -34,6 +34,7 @@ import (
 	ackmetrics "github.com/aws-controllers-k8s/runtime/pkg/metrics"
 	ackrtcache "github.com/aws-controllers-k8s/runtime/pkg/runtime/cache"
 	acktypes "github.com/aws-controllers-k8s/runtime/pkg/types"
+	ackutil "github.com/aws-controllers-k8s/runtime/pkg/util"
 )
 
 const (
@@ -271,7 +272,33 @@ func (c *serviceController) BindControllerManager(mgr ctrlrt.Manager, cfg ackcfg
 		c.fieldExportReconciler = rec
 	}
 
-	for _, rmf := range c.rmFactories {
+	// Get the list of resources to reconcile from the config
+	reconcileResources, err := cfg.GetReconcileResources()
+	if err != nil {
+		return fmt.Errorf("error parsing reconcile resources: %v", err)
+	}
+
+	if len(reconcileResources) == 0 {
+		c.log.Info("No resources? Did they all go on vacation? Defaulting to reconciling all resources.")
+	}
+	// Filter the resource manager factories
+	filteredRMFs := c.rmFactories
+	if len(reconcileResources) > 0 {
+		filteredRMFs = make(map[string]acktypes.AWSResourceManagerFactory)
+		for key, rmf := range c.rmFactories {
+			rd := rmf.ResourceDescriptor()
+			resourceKind := rd.GroupVersionKind().Kind
+
+			if ackutil.InStrings(resourceKind, reconcileResources) {
+				filteredRMFs[key] = rmf
+				c.log.Info("including reconciler for resource kind", "kind", resourceKind)
+			} else {
+				c.log.Info("excluding reconciler for resource kind", "kind", resourceKind, "reason", "not in reconcile-resources flag")
+			}
+		}
+	}
+
+	for _, rmf := range filteredRMFs {
 		rec := NewReconciler(c, rmf, c.log, cfg, c.metrics, cache)
 		if err := rec.BindControllerManager(mgr); err != nil {
 			return err