Select matching AlertmanagerConfigs

This copies what the prometheus controller does for things like
ServiceMonitors.

pkg/alertmanager/operator.go

@@ -635,6 +635,13 @@ func (c *Operator) sync(ctx context.Context, key string) error {
 }
 
 func (c *Operator) provisionAlertmanagerConfiguration(ctx context.Context, am *monitoringv1.Alertmanager) error {
+	// If no AlertmanagerConfig selectors are configured, the user wants to
+	// manage configuration themselves.
+	if am.Spec.AlertmanagerConfigSelector == nil {
+		level.Debug(c.logger).Log("msg", ", no AlertmanagerConfig selector specified, leaving configuration unmanaged", "alertmanager", am.Name, "namespace", am.Namespace)
+		return nil
+	}
+
 	secretName := defaultConfigSecretName(am.Name)
 	if am.Spec.ConfigSecret != "" {
 		secretName = am.Spec.ConfigSecret
@@ -679,7 +686,12 @@ func (c *Operator) provisionAlertmanagerConfiguration(ctx context.Context, am *m
 		return errors.New("default route must be configured")
 	}
 
-	// build routes, receivers and inhibit rules from AlertmanagerConfigs here
+	amcs, err := c.selectAlertManagerConfigs(am)
+	if err != nil {
+		return errors.Wrap(err, "selecting AlertmanagerConfigs failed")
+	}
+
+	level.Info(c.logger).Log("msg", "amcs", "amcs", amcs, "namespace", am.Namespace, "alertmanager", am.Name)
 
 	if foundReceivers {
 		// just append receivrs from AlertmanagerConfig CRs, otherwise must first create receivers field
@@ -692,6 +704,64 @@ func (c *Operator) provisionAlertmanagerConfiguration(ctx context.Context, am *m
 	return nil
 }
 
+func (c *Operator) selectAlertManagerConfigs(am *monitoringv1.Alertmanager) (map[string]*monitoringv1.AlertmanagerConfig, error) {
+	namespaces := []string{}
+	// Selectors (<namespace>/<name>) might overlap. Deduplicate them along the keyFunc.
+	res := make(map[string]*monitoringv1.AlertmanagerConfig)
+
+	amConfigSelector, err := metav1.LabelSelectorAsSelector(am.Spec.AlertmanagerConfigSelector)
+	if err != nil {
+		return nil, err
+	}
+
+	// If 'AlertmanagerConfigNamespaceSelector' is nil, only check own namespace.
+	if am.Spec.AlertmanagerConfigNamespaceSelector == nil {
+		namespaces = append(namespaces, am.Namespace)
+	} else {
+		amConfigNSSelector, err := metav1.LabelSelectorAsSelector(am.Spec.AlertmanagerConfigNamespaceSelector)
+		if err != nil {
+			return nil, err
+		}
+
+		namespaces, err = c.listMatchingNamespaces(amConfigNSSelector)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	level.Debug(c.logger).Log("msg", "filtering namespaces to select AlertmanagerConfigs from", "namespaces", strings.Join(namespaces, ","), "namespace", am.Namespace, "alertmanager", am.Name)
+
+	for _, ns := range namespaces {
+		c.alrtCfgInfs.ListAllByNamespace(ns, amConfigSelector, func(obj interface{}) {
+			k, ok := c.keyFunc(obj)
+			if ok {
+				res[k] = obj.(*monitoringv1.AlertmanagerConfig)
+			}
+		})
+	}
+
+	alertmanagerConfigs := []string{}
+	for k := range res {
+		alertmanagerConfigs = append(alertmanagerConfigs, k)
+	}
+	level.Debug(c.logger).Log("msg", "selected AlertmanagerConfigs", "aletmanagerconfigs", strings.Join(alertmanagerConfigs, ","), "namespace", am.Namespace, "prometheus", am.Name)
+
+	return res, nil
+}
+
+// listMatchingNamespaces lists all the namespaces that match the provided
+// selector.
+func (c *Operator) listMatchingNamespaces(selector labels.Selector) ([]string, error) {
+	var ns []string
+	err := cache.ListAll(c.nsAlrtInf.GetStore(), selector, func(obj interface{}) {
+		ns = append(ns, obj.(*v1.Namespace).Name)
+	})
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to list namespaces")
+	}
+	return ns, nil
+}
+
 //checkAlertmanagerSpecDeprecation checks for deprecated fields in the prometheus spec and logs a warning if applicable
 func checkAlertmanagerSpecDeprecation(key string, a *monitoringv1.Alertmanager, logger log.Logger) {
 	deprecationWarningf := "alertmanager key=%v, field %v is deprecated, '%v' field should be used instead"