Alerting: Configure alert manager data source as an external AM (#52081)

Co-authored-by: Jean-Philippe Quéméner <JohnnyQQQQ@users.noreply.github.com>
Co-authored-by: gotjosh <josue.abreu@gmail.com>
Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

pkg/services/ngalert/sender/router.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/benbjohnson/clock"
 
+	"github.com/grafana/grafana/pkg/api/datasource"
 	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/services/datasources"
 	"github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
@@ -126,6 +127,8 @@ func (d *AlertsRouter) SyncAndApplyConfigFromDatabase() error {
 			continue
 		}
 
+		d.logger.Debug("alertmanagers found in the configuration", "alertmanagers", cfg.Alertmanagers)
+
 		// We have a running sender, check if we need to apply a new config.
 		if ok {
 			if d.externalAlertmanagersCfgHash[cfg.OrgID] == cfg.AsSHA256() {
@@ -218,16 +221,17 @@ func (d *AlertsRouter) alertmanagersFromDatasources(orgID int64) ([]string, erro
 }
 
 func (d *AlertsRouter) buildExternalURL(ds *datasources.DataSource) (string, error) {
-	amURL := ds.Url
-	// if basic auth is enabled we need to build the url with basic auth baked in
-	if !ds.BasicAuth {
-		return amURL, nil
-	}
-
-	parsed, err := url.Parse(ds.Url)
+	// We re-use the same parsing logic as the datasource to make sure it matches whatever output the user received
+	// when doing the healthcheck.
+	parsed, err := datasource.ValidateURL(datasources.DS_ALERTMANAGER, ds.Url)
 	if err != nil {
 		return "", fmt.Errorf("failed to parse alertmanager datasource url: %w", err)
 	}
+	// if basic auth is enabled we need to build the url with basic auth baked in
+	if !ds.BasicAuth {
+		return parsed.String(), nil
+	}
+
 	password := d.secretService.GetDecryptedValue(context.Background(), ds.SecureJsonData, "basicAuthPassword", "")
 	if password == "" {
 		return "", fmt.Errorf("basic auth enabled but no password set")