Disable controllers using a command-line flag (#2339)

* Disable controllers using a flag

This patch allows disabling controllers when using a new `Main` function
called `MainNamed` which takes a list of `NamedControllerConstructor`.

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

* Apply reviews

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

* Add comments, split filter and conversion

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

* Allocate len(ctors)

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

* to disable -> disabling

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

injection/interface.go

@@ -103,6 +103,14 @@ type DynamicInterface interface {
 
 type ControllerConstructor func(context.Context, configmap.Watcher) *controller.Impl
 
+// NamedControllerConstructor is a ControllerConstructor with an associated name.
+type NamedControllerConstructor struct {
+	// Name is the name associated with the controller returned by ControllerConstructor.
+	Name string
+	// ControllerConstructor is a constructor for a controller.
+	ControllerConstructor ControllerConstructor
+}
+
 var (
 	// Check that impl implements Interface
 	_ Interface = (*impl)(nil)

injection/sharedmain/main.go

@@ -26,6 +26,8 @@ import (
 	"os"
 	"time"
 
+	"github.com/spf13/pflag"
+
 	"go.uber.org/automaxprocs/maxprocs" // automatically set GOMAXPROCS based on cgroups
 	"go.uber.org/zap"
 	"golang.org/x/sync/errgroup"
@@ -34,6 +36,7 @@ import (
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/client-go/rest"
 
@@ -111,6 +114,43 @@ var (
 	WebhookMainWithConfig  = MainWithConfig
 )
 
+// MainNamed runs the generic main flow for controllers and webhooks.
+//
+// In addition to the MainWithConfig flow, it defines a `disabled-controllers` flag that allows disabling controllers
+// by name.
+func MainNamed(ctx context.Context, component string, ctors ...injection.NamedControllerConstructor) {
+
+	disabledControllers := pflag.StringSlice("disable-controllers", []string{}, "Comma-separated list of disabled controllers.")
+
+	// HACK: This parses flags, so the above should be set once this runs.
+	cfg := injection.ParseAndGetRESTConfigOrDie()
+
+	enabledCtors := enabledControllers(*disabledControllers, ctors)
+
+	MainWithConfig(ctx, component, cfg, toControllerConstructors(enabledCtors)...)
+}
+
+func enabledControllers(disabledControllers []string, ctors []injection.NamedControllerConstructor) []injection.NamedControllerConstructor {
+	disabledControllersSet := sets.NewString(disabledControllers...)
+	activeCtors := make([]injection.NamedControllerConstructor, 0, len(ctors))
+	for _, ctor := range ctors {
+		if disabledControllersSet.Has(ctor.Name) {
+			log.Printf("Disabling controller %s", ctor.Name)
+			continue
+		}
+		activeCtors = append(activeCtors, ctor)
+	}
+	return activeCtors
+}
+
+func toControllerConstructors(namedCtors []injection.NamedControllerConstructor) []injection.ControllerConstructor {
+	ctors := make([]injection.ControllerConstructor, 0, len(namedCtors))
+	for _, ctor := range namedCtors {
+		ctors = append(ctors, ctor.ControllerConstructor)
+	}
+	return ctors
+}
+
 // MainWithContext runs the generic main flow for controllers and
 // webhooks. Use MainWithContext if you do not need to serve webhooks.
 func MainWithContext(ctx context.Context, component string, ctors ...injection.ControllerConstructor) {

injection/sharedmain/main_test.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2021 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package sharedmain
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+
+	"knative.dev/pkg/injection"
+)
+
+func TestEnabledControllers(t *testing.T) {
+	tests := []struct {
+		name                string
+		disabledControllers []string
+		ctors               []injection.NamedControllerConstructor
+		wantNames           []string
+	}{
+		{
+			name:                "zero",
+			disabledControllers: []string{"foo"},
+			ctors:               []injection.NamedControllerConstructor{{Name: "bar"}},
+			wantNames:           []string{"bar"},
+		},
+		{
+			name:                "one",
+			disabledControllers: []string{"foo"},
+			ctors:               []injection.NamedControllerConstructor{{Name: "foo"}},
+			wantNames:           []string{},
+		},
+		{
+			name:                "two",
+			disabledControllers: []string{"foo"},
+			ctors: []injection.NamedControllerConstructor{
+				{Name: "foo"},
+				{Name: "bar"},
+			},
+			wantNames: []string{"bar"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := enabledControllers(tt.disabledControllers, tt.ctors)
+			if diff := cmp.Diff(tt.wantNames, namesOf(got)); diff != "" {
+				t.Error("(-want, +got)", diff)
+			}
+		})
+	}
+}
+
+func namesOf(ctors []injection.NamedControllerConstructor) []string {
+	names := make([]string, 0, len(ctors))
+	for _, x := range ctors {
+		names = append(names, x.Name)
+	}
+	return names
+}