[Elastic Agent] Fix lazy acker to only add new actions to the batch (#…

…27981) (#28062)

* Fix lazy acker.

* Add changelog.

(cherry picked from commit bdec63a)

Co-authored-by: Blake Rouse <blake.rouse@elastic.co>

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -87,6 +87,7 @@
 - Add "_monitoring" suffix to monitoring instance names to remove ambiguity with the status command. {issue}25449[25449]
 - Ignore ErrNotExists when fixing permissions. {issue}27836[27836] {pull}27846[27846]
 - Snapshot artifact lookup will use agent.download proxy settings. {issue}27903[27903] {pull}27904[27904]
+- Fix lazy acker to only add new actions to the batch. {pull}27981[27981]
 
 ==== New features
 

x-pack/elastic-agent/pkg/fleetapi/acker/lazy/lazy_acker.go

@@ -37,8 +37,7 @@ func NewAcker(baseAcker batchAcker, log *logger.Logger) *Acker {
 
 // Ack acknowledges action.
 func (f *Acker) Ack(ctx context.Context, action fleetapi.Action) error {
-	f.queue = append(f.queue, action)
-	f.log.Debugf("appending action with id '%s' to the queue", action.ID())
+	f.enqueue(action)
 
 	if _, isAckForced := action.(ackForcer); isAckForced {
 		return f.Commit(ctx)
@@ -58,3 +57,14 @@ func (f *Acker) Commit(ctx context.Context) error {
 	f.queue = make([]fleetapi.Action, 0)
 	return nil
 }
+
+func (f *Acker) enqueue(action fleetapi.Action) {
+	for _, a := range f.queue {
+		if a.ID() == action.ID() {
+			f.log.Debugf("action with id '%s' has already been queued", action.ID())
+			return
+		}
+	}
+	f.queue = append(f.queue, action)
+	f.log.Debugf("appending action with id '%s' to the queue", action.ID())
+}

x-pack/elastic-agent/pkg/fleetapi/acker/lazy/lazy_acker_test.go

@@ -79,12 +79,21 @@ func TestLazyAcker(t *testing.T) {
 	}()
 	c := context.Background()
 
+	if err := lacker.Ack(c, testAction1); err != nil {
+		t.Fatal(err)
+	}
 	if err := lacker.Ack(c, testAction1); err != nil {
 		t.Fatal(err)
 	}
 	if err := lacker.Ack(c, testAction2); err != nil {
 		t.Fatal(err)
 	}
+	if err := lacker.Ack(c, testAction2); err != nil {
+		t.Fatal(err)
+	}
+	if err := lacker.Ack(c, testAction3); err != nil {
+		t.Fatal(err)
+	}
 	if err := lacker.Ack(c, testAction3); err != nil {
 		t.Fatal(err)
 	}