AlertingNG: Refactor notifier to support config reloads (#32099)

* AlertingNG: Refactor notifier to support config reloads

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Fix review comments and make reloading of config a sync operation

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Fix review comments

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

pkg/services/ngalert/notifier/alert_reception.go

@@ -2,6 +2,7 @@ package notifier
 
 import (
 	"context"
+	"sync"
 	"time"
 
 	"github.com/go-kit/kit/log"
@@ -30,6 +31,7 @@ type AlertProvider struct {
 	// GetPendingLegacy() AlertIterator, and the external code will use this
 	// iterator to send to the stage.
 	stage    notify.Stage
+	stageMtx sync.Mutex
 }
 
 // NewAlertProvider returns AlertProvider that also supports legacy alerts via PutPostableAlert.
@@ -77,8 +79,10 @@ func (ap *AlertProvider) PutPostableAlert(alerts ...*PostableAlert) error {
 	}
 
 	for recv, alerts := range groupedAlerts {
+		ap.stageMtx.Lock()
 		ctx := notify.WithReceiverName(context.Background(), recv)
 		_, _, err := ap.stage.Exec(ctx, ap.logger, alerts...)
+		ap.stageMtx.Unlock()
 		if err != nil {
 			return err
 		}
@@ -87,6 +91,12 @@ func (ap *AlertProvider) PutPostableAlert(alerts ...*PostableAlert) error {
 	return nil
 }
 
+func (ap *AlertProvider) SetStage(s notify.Stage) {
+	ap.stageMtx.Lock()
+	defer ap.stageMtx.Unlock()
+	ap.stage = s
+}
+
 func alertForDelivery(a *PostableAlert) *types.Alert {
 	lbls := model.LabelSet{}
 	annotations := model.LabelSet{}

pkg/services/ngalert/notifier/alertmanager.go

@@ -20,6 +20,7 @@ import (
 	"github.com/prometheus/alertmanager/types"
 	"github.com/prometheus/client_golang/prometheus"
 
+	"github.com/grafana/alerting-api/pkg/api"
 	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/registry"
 	"github.com/grafana/grafana/pkg/setting"
@@ -34,9 +35,11 @@ type Alertmanager struct {
 	silences *silence.Silences
 	marker   types.Marker
 	alerts   *AlertProvider
-	dispatcher *dispatch.Dispatcher
 
-	wg sync.WaitGroup
+	dispatcher   *dispatch.Dispatcher
+	dispatcherWG sync.WaitGroup
+
+	reloadConfigMtx sync.Mutex
 }
 
 func init() {
@@ -47,25 +50,11 @@ func (am *Alertmanager) IsDisabled() bool {
 	return !setting.AlertingEnabled || !setting.ExecuteAlerts
 }
 
-func (am *Alertmanager) Init() error {
+func (am *Alertmanager) Init() (err error) {
 	am.logger = log.New("alertmanager")
-
-	return nil
-}
-
-func (am *Alertmanager) Run(ctx context.Context) error {
 	//TODO: Speak with David Parrot wrt to the marker, we'll probably need our own.
 	am.marker = types.NewMarker(prometheus.DefaultRegisterer)
 
-	var err error
-	am.silences, err = silence.New(silence.Options{
-		SnapshotFile: filepath.Join("dir", "silences"), //TODO: This is a setting
-		Retention:    time.Hour * 24,                   //TODO: This is also a setting
-	})
-	if err != nil {
-		return errors.Wrap(err, "unable to initialize the silencing component of alerting")
-	}
-
 	am.notificationLog, err = nflog.New(
 		nflog.WithRetention(time.Hour*24),                         //TODO: This is a setting.
 		nflog.WithSnapshot(filepath.Join("dir", "notifications")), //TODO: This should be a setting
@@ -73,8 +62,65 @@ func (am *Alertmanager) Run(ctx context.Context) error {
 	if err != nil {
 		return errors.Wrap(err, "unable to initialize the notification log component of alerting")
 	}
+	am.silences, err = silence.New(silence.Options{
+		SnapshotFile: filepath.Join("dir", "silences"), //TODO: This is a setting
+		Retention:    time.Hour * 24,                   //TODO: This is also a setting
+	})
+	if err != nil {
+		return errors.Wrap(err, "unable to initialize the silencing component of alerting")
+	}
 
-	{
+	return nil
+}
+
+func (am *Alertmanager) Run(ctx context.Context) error {
+	// Make sure dispatcher starts. We can tolerate future reload failures.
+	if err := am.ReloadConfigFromDatabase(); err != nil {
+		return err
+	}
+	for {
+		select {
+		case <-ctx.Done():
+			am.StopAndWait()
+			return nil
+		case <-time.After(1 * time.Minute):
+			// TODO: once we have a check to skip reload on same config, uncomment this.
+			//if err := am.ReloadConfigFromDatabase(); err != nil {
+			//	am.logger.Error("failed to sync config from database", "error", err)
+			//}
+		}
+	}
+}
+
+func (am *Alertmanager) StopAndWait() {
+	if am.dispatcher != nil {
+		am.dispatcher.Stop()
+	}
+	am.dispatcherWG.Wait()
+}
+
+// ReloadConfigFromDatabase picks the latest config from database and restarts
+// the components with the new config.
+func (am *Alertmanager) ReloadConfigFromDatabase() error {
+	am.reloadConfigMtx.Lock()
+	defer am.reloadConfigMtx.Unlock()
+
+	// TODO: check if config is same as before using hashes and skip reload in case they are same.
+	cfg, err := getConfigFromDatabase()
+	if err != nil {
+		return errors.Wrap(err, "get config from database")
+	}
+	return errors.Wrap(am.ApplyConfig(cfg), "reload from config")
+}
+
+func getConfigFromDatabase() (*api.PostableApiAlertingConfig, error) {
+	// TODO: get configs from the database.
+	return &api.PostableApiAlertingConfig{}, nil
+}
+
+// ApplyConfig applies a new configuration by re-initializing all components using the configuration provided.
+// It is not safe to call concurrently.
+func (am *Alertmanager) ApplyConfig(cfg *api.PostableApiAlertingConfig) error {
 	// Now, let's put together our notification pipeline
 	receivers := buildIntegrationsMap()
 	routingStage := make(notify.RoutingStage, len(receivers))
@@ -86,16 +132,17 @@ func (am *Alertmanager) Run(ctx context.Context) error {
 		routingStage[name] = notify.MultiStage{silencingStage, stage}
 	}
 
-		am.alerts, err = NewAlertProvider(routingStage, am.marker, gokit_log.NewNopLogger())
-		if err != nil {
-			return errors.Wrap(err, "failed to initialize alerting storage component")
-		}
+	am.alerts.SetStage(routingStage)
 
+	am.StopAndWait()
 	am.dispatcher = dispatch.NewDispatcher(am.alerts, BuildRoutingConfiguration(), routingStage, am.marker, timeoutFunc, gokit_log.NewNopLogger(), nil)
-	}
 
-	am.wg.Add(1)
-	go am.dispatcher.Run()
+	am.dispatcherWG.Add(1)
+	go func() {
+		defer am.dispatcherWG.Done()
+		am.dispatcher.Run()
+	}()
+
 	return nil
 }