Support custom watches on controller

.changelog/18439.txt

@@ -0,0 +1,3 @@
+```release-note:feature
+Support custom watches on the Consul Controller framework.
+```

internal/controller/api.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/hashicorp/go-hclog"
 
+	"github.com/hashicorp/consul/agent/consul/controller/queue"
 	"github.com/hashicorp/consul/internal/resource"
 	"github.com/hashicorp/consul/proto-public/pbresource"
 )
@@ -46,6 +47,21 @@ func (c Controller) WithWatch(watchedType *pbresource.Type, mapper DependencyMap
 	return c
 }
 
+// WithCustomWatch adds a custom watch on the given dependency to the controller. Custom mapper
+// will be called to map events produced by source to the controller's watched type.
+func (c Controller) WithCustomWatch(source *Source, mapper CustomDependencyMapper) Controller {
+	if source == nil {
+		panic("source must not be nil")
+	}
+
+	if mapper == nil {
+		panic("mapper must not be nil")
+	}
+
+	c.customWatches = append(c.customWatches, customWatch{source, mapper})
+	return c
+}
+
 // WithLogger changes the controller's logger.
 func (c Controller) WithLogger(logger hclog.Logger) Controller {
 	if logger == nil {
@@ -107,20 +123,60 @@ func (c Controller) backoff() (time.Duration, time.Duration) {
 // Use the builder methods in this package (starting with ForType) to construct
 // a controller, and then pass it to a Manager to be executed.
 type Controller struct {
-	managedType *pbresource.Type
-	reconciler  Reconciler
-	logger      hclog.Logger
-	watches     []watch
-	baseBackoff time.Duration
-	maxBackoff  time.Duration
-	placement   Placement
+	managedType   *pbresource.Type
+	reconciler    Reconciler
+	logger        hclog.Logger
+	watches       []watch
+	customWatches []customWatch
+	baseBackoff   time.Duration
+	maxBackoff    time.Duration
+	placement     Placement
 }
 
 type watch struct {
 	watchedType *pbresource.Type
 	mapper      DependencyMapper
 }
 
+// Watch is responsible for watching for custom events from source and adding them to
+// the event queue.
+func (s *Source) Watch(ctx context.Context, add func(e Event)) error {
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case evt, ok := <-s.Source:
+			if !ok {
+				return nil
+			}
+			add(evt)
+		}
+	}
+}
+
+// Source is used as a generic source of events. This can be used when events aren't coming from resources
+// stored by the resource API.
+type Source struct {
+	Source <-chan Event
+}
+
+// Event captures an event in the system which the API can choose to respond to.
+type Event struct {
+	Obj queue.ItemType
+}
+
+// Key returns a string that will be used to de-duplicate items in the queue.
+func (e Event) Key() string {
+	return e.Obj.Key()
+}
+
+// customWatch represent a Watch on a custom Event source and a Mapper to map said
+// Events into Requests that the controller can respond to.
+type customWatch struct {
+	source *Source
+	mapper CustomDependencyMapper
+}
+
 // Request represents a request to reconcile the resource with the given ID.
 type Request struct {
 	// ID of the resource that needs to be reconciled.

internal/controller/api_test.go

@@ -25,9 +25,20 @@ func TestController_API(t *testing.T) {
 	rec := newTestReconciler()
 	client := svctest.RunResourceService(t, demo.RegisterTypes)
 
+	concertsChan := make(chan controller.Event)
+	defer close(concertsChan)
+	concertSource := &controller.Source{Source: concertsChan}
+	concertMapper := func(ctx context.Context, rt controller.Runtime, event controller.Event) ([]controller.Request, error) {
+		artistID := event.Obj.(*Concert).artistID
+		var requests []controller.Request
+		requests = append(requests, controller.Request{ID: artistID})
+		return requests, nil
+	}
+
 	ctrl := controller.
 		ForType(demo.TypeV2Artist).
 		WithWatch(demo.TypeV2Album, controller.MapOwner).
+		WithCustomWatch(concertSource, concertMapper).
 		WithBackoff(10*time.Millisecond, 100*time.Millisecond).
 		WithReconciler(rec)
 
@@ -69,6 +80,32 @@ func TestController_API(t *testing.T) {
 		prototest.AssertDeepEqual(t, rsp.Resource.Id, req.ID)
 	})
 
+	t.Run("custom watched resource type", func(t *testing.T) {
+		res, err := demo.GenerateV2Artist()
+		require.NoError(t, err)
+
+		rsp, err := client.Write(testContext(t), &pbresource.WriteRequest{Resource: res})
+		require.NoError(t, err)
+
+		req := rec.wait(t)
+		prototest.AssertDeepEqual(t, rsp.Resource.Id, req.ID)
+
+		rec.expectNoRequest(t, 500*time.Millisecond)
+
+		concertsChan <- controller.Event{Obj: &Concert{name: "test-concert", artistID: rsp.Resource.Id}}
+
+		watchedReq := rec.wait(t)
+		prototest.AssertDeepEqual(t, req.ID, watchedReq.ID)
+
+		otherArtist, err := demo.GenerateV2Artist()
+		require.NoError(t, err)
+
+		concertsChan <- controller.Event{Obj: &Concert{name: "test-concert", artistID: otherArtist.Id}}
+
+		watchedReq = rec.wait(t)
+		prototest.AssertDeepEqual(t, otherArtist.Id, watchedReq.ID)
+	})
+
 	t.Run("error retries", func(t *testing.T) {
 		rec.failNext(errors.New("KABOOM"))
 
@@ -266,3 +303,12 @@ func testContext(t *testing.T) context.Context {
 
 	return ctx
 }
+
+type Concert struct {
+	name     string
+	artistID *pbresource.ID
+}
+
+func (c Concert) Key() string {
+	return c.name
+}

internal/controller/controller.go

@@ -40,20 +40,39 @@ func (c *controllerRunner) run(ctx context.Context) error {
 		})
 	})
 
-	for _, watch := range c.ctrl.watches {
-		watch := watch
+	for _, w := range c.ctrl.watches {
 		mapQueue := runQueue[mapperRequest](groupCtx, c.ctrl)
-
+		watcher := w
 		// Watched Type Events → Mapper Queue
 		group.Go(func() error {
-			return c.watch(groupCtx, watch.watchedType, func(res *pbresource.Resource) {
+			return c.watch(groupCtx, watcher.watchedType, func(res *pbresource.Resource) {
 				mapQueue.Add(mapperRequest{res: res})
 			})
 		})
 
 		// Mapper Queue → Mapper → Reconciliation Queue
 		group.Go(func() error {
-			return c.runMapper(groupCtx, watch, mapQueue, recQueue)
+			return c.runMapper(groupCtx, watcher, mapQueue, recQueue, func(ctx context.Context, runtime Runtime, itemType queue.ItemType) ([]Request, error) {
+				return watcher.mapper(ctx, runtime, itemType.(mapperRequest).res)
+			})
+		})
+	}
+
+	for _, cw := range c.ctrl.customWatches {
+		customMapQueue := runQueue[Event](groupCtx, c.ctrl)
+		watcher := cw
+		// Custom Events → Mapper Queue
+		group.Go(func() error {
+			return watcher.source.Watch(groupCtx, func(e Event) {
+				customMapQueue.Add(e)
+			})
+		})
+
+		// Mapper Queue → Mapper → Reconciliation Queue
+		group.Go(func() error {
+			return c.runCustomMapper(groupCtx, watcher, customMapQueue, recQueue, func(ctx context.Context, runtime Runtime, itemType queue.ItemType) ([]Request, error) {
+				return watcher.mapper(ctx, runtime, itemType.(Event))
+			})
 		})
 	}
 
@@ -71,7 +90,7 @@ func runQueue[T queue.ItemType](ctx context.Context, ctrl Controller) queue.Work
 }
 
 func (c *controllerRunner) watch(ctx context.Context, typ *pbresource.Type, add func(*pbresource.Resource)) error {
-	watch, err := c.client.WatchList(ctx, &pbresource.WatchListRequest{
+	wl, err := c.client.WatchList(ctx, &pbresource.WatchListRequest{
 		Type: typ,
 		Tenancy: &pbresource.Tenancy{
 			Partition: storage.Wildcard,
@@ -85,7 +104,7 @@ func (c *controllerRunner) watch(ctx context.Context, typ *pbresource.Type, add
 	}
 
 	for {
-		event, err := watch.Recv()
+		event, err := wl.Recv()
 		if err != nil {
 			c.logger.Warn("error received from watch", "error", err)
 			return err
@@ -99,6 +118,7 @@ func (c *controllerRunner) runMapper(
 	w watch,
 	from queue.WorkQueue[mapperRequest],
 	to queue.WorkQueue[Request],
+	mapper func(ctx context.Context, runtime Runtime, itemType queue.ItemType) ([]Request, error),
 ) error {
 	logger := c.logger.With("watched_resource_type", resource.ToGVK(w.watchedType))
 
@@ -108,34 +128,66 @@ func (c *controllerRunner) runMapper(
 			return nil
 		}
 
-		var reqs []Request
-		err := c.handlePanic(func() error {
-			var err error
-			reqs, err = w.mapper(ctx, c.runtime(), item.res)
-			return err
-		})
-		if err != nil {
+		if err := c.doMap(ctx, mapper, to, item, logger); err != nil {
 			from.AddRateLimited(item)
 			from.Done(item)
 			continue
 		}
 
-		for _, r := range reqs {
-			if !resource.EqualType(r.ID.Type, c.ctrl.managedType) {
-				logger.Error("dependency mapper returned request for a resource of the wrong type",
-					"type_expected", resource.ToGVK(c.ctrl.managedType),
-					"type_got", resource.ToGVK(r.ID.Type),
-				)
-				continue
-			}
-			to.Add(r)
+		from.Forget(item)
+		from.Done(item)
+	}
+}
+
+func (c *controllerRunner) runCustomMapper(
+	ctx context.Context,
+	cw customWatch,
+	from queue.WorkQueue[Event],
+	to queue.WorkQueue[Request],
+	mapper func(ctx context.Context, runtime Runtime, itemType queue.ItemType) ([]Request, error),
+) error {
+	logger := c.logger.With("watched_event", cw.source)
+
+	for {
+		item, shutdown := from.Get()
+		if shutdown {
+			return nil
+		}
+
+		if err := c.doMap(ctx, mapper, to, item, logger); err != nil {
+			from.AddRateLimited(item)
+			from.Done(item)
+			continue
 		}
 
 		from.Forget(item)
 		from.Done(item)
 	}
 }
 
+func (c *controllerRunner) doMap(ctx context.Context, mapper func(ctx context.Context, runtime Runtime, itemType queue.ItemType) ([]Request, error), to queue.WorkQueue[Request], item queue.ItemType, logger hclog.Logger) error {
+	var reqs []Request
+	if err := c.handlePanic(func() error {
+		var err error
+		reqs, err = mapper(ctx, c.runtime(), item)
+		return err
+	}); err != nil {
+		return err
+	}
+
+	for _, r := range reqs {
+		if !resource.EqualType(r.ID.Type, c.ctrl.managedType) {
+			logger.Error("dependency mapper returned request for a resource of the wrong type",
+				"type_expected", resource.ToGVK(c.ctrl.managedType),
+				"type_got", resource.ToGVK(r.ID.Type),
+			)
+			continue
+		}
+		to.Add(r)
+	}
+	return nil
+}
+
 func (c *controllerRunner) runReconciler(ctx context.Context, queue queue.WorkQueue[Request]) error {
 	for {
 		req, shutdown := queue.Get()

internal/controller/dependency_mappers.go

@@ -18,6 +18,14 @@ type DependencyMapper func(
 	res *pbresource.Resource,
 ) ([]Request, error)
 
+// CustomDependencyMapper is called when an Event occurs to determine which of the
+// controller's managed resources need to be reconciled.
+type CustomDependencyMapper func(
+	ctx context.Context,
+	rt Runtime,
+	event Event,
+) ([]Request, error)
+
 // MapOwner implements a DependencyMapper that returns the updated resource's owner.
 func MapOwner(_ context.Context, _ Runtime, res *pbresource.Resource) ([]Request, error) {
 	var reqs []Request