add --disabled-controllers

cmd/api-syncagent/main.go

@@ -21,6 +21,7 @@ import (
 	"flag"
 	"fmt"
 	golog "log"
+	"slices"
 	"strings"
 
 	"github.com/go-logr/zapr"
@@ -46,6 +47,7 @@ import (
 	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/clientcmd"
 	ctrlruntime "sigs.k8s.io/controller-runtime"
@@ -57,6 +59,8 @@ import (
 	metricsserver "sigs.k8s.io/controller-runtime/pkg/metrics/server"
 )
 
+var availableControllers = sets.New("apiexport", "apiresourceschema", "sync")
+
 func main() {
 	ctx := context.Background()
 
@@ -133,16 +137,37 @@ func run(ctx context.Context, log *zap.SugaredLogger, opts *Options) error {
 		return fmt.Errorf("failed to add kcp cluster runnable: %w", err)
 	}
 
-	if err := apiresourceschema.Add(mgr, kcpCluster, lcName, log, 4, opts.AgentName, opts.PublishedResourceSelector); err != nil {
-		return fmt.Errorf("failed to add apiresourceschema controller: %w", err)
+	startController := func(name string, creator func() error) error {
+		if slices.Contains(opts.DisabledControllers, name) {
+			log.Infof("Not starting %s controller because it is disabled.", name)
+			return nil
+		}
+
+		if err := creator(); err != nil {
+			return fmt.Errorf("failed to add %s controller: %w", name, err)
+		}
+
+		return nil
+	}
+
+	if err := startController("apiresourceschema", func() error {
+		return apiresourceschema.Add(mgr, kcpCluster, lcName, log, 4, opts.AgentName, opts.PublishedResourceSelector)
+	}); err != nil {
+		return err
 	}
 
-	if err := apiexport.Add(mgr, kcpCluster, lcName, log, opts.APIExportRef, opts.AgentName, opts.PublishedResourceSelector); err != nil {
-		return fmt.Errorf("failed to add apiexport controller: %w", err)
+	if err := startController("apiexport", func() error {
+		return apiexport.Add(mgr, kcpCluster, lcName, log, opts.APIExportRef, opts.AgentName, opts.PublishedResourceSelector)
+	}); err != nil {
+		return err
 	}
 
-	if err := syncmanager.Add(ctx, mgr, kcpCluster, kcpRestConfig, log, apiExport, opts.PublishedResourceSelector, opts.Namespace, opts.AgentName); err != nil {
-		return fmt.Errorf("failed to add syncmanager controller: %w", err)
+	// This controller is called "sync" because it makes the most sense to the users, even though internally the relevant
+	// controller is the syncmanager (which in turn would start/stop the sync controllers).
+	if err := startController("sync", func() error {
+		return syncmanager.Add(ctx, mgr, kcpCluster, kcpRestConfig, log, apiExport, opts.PublishedResourceSelector, opts.Namespace, opts.AgentName)
+	}); err != nil {
+		return err
 	}
 
 	log.Info("Starting kcp Sync Agent…")

cmd/api-syncagent/options.go

@@ -26,6 +26,7 @@ import (
 
 	"k8s.io/apimachinery/pkg/labels"
 	utilerrors "k8s.io/apimachinery/pkg/util/errors"
+	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/validation"
 )
 
@@ -68,6 +69,8 @@ type Options struct {
 
 	MetricsAddr string
 	HealthAddr  string
+
+	DisabledControllers []string
 }
 
 func NewOptions() *Options {
@@ -91,6 +94,7 @@ func (o *Options) AddFlags(flags *pflag.FlagSet) {
 	flags.StringVar(&o.KubeconfigCAFileOverride, "kubeconfig-ca-file-override", o.KubeconfigCAFileOverride, "override the server CA file configured in the local kubeconfig")
 	flags.StringVar(&o.MetricsAddr, "metrics-address", o.MetricsAddr, "host and port to serve Prometheus metrics via /metrics (HTTP)")
 	flags.StringVar(&o.HealthAddr, "health-address", o.HealthAddr, "host and port to serve probes via /readyz and /healthz (HTTP)")
+	flags.StringSliceVar(&o.DisabledControllers, "disabled-controllers", o.DisabledControllers, fmt.Sprintf("comma-separated list of controllers (out of %v) to disable (can be given multiple times)", sets.List(availableControllers)))
 }
 
 func (o *Options) Validate() error {
@@ -124,6 +128,13 @@ func (o *Options) Validate() error {
 		}
 	}
 
+	disabled := sets.New(o.DisabledControllers...)
+	unknown := disabled.Difference(availableControllers)
+
+	if unknown.Len() > 0 {
+		errs = append(errs, fmt.Errorf("unknown controller(s) %v, mut be any of %v", sets.List(unknown), sets.List(availableControllers)))
+	}
+
 	return utilerrors.NewAggregate(errs)
 }