Add system.prometheus.server.alertmanager.dns

Change-Id: I25ecdadfa1b854053e98f553bf6acacb0c37edd9
diff --git a/classes/cluster/virtual-mcp11-k8s-calico/stacklight/server.yml b/classes/cluster/virtual-mcp11-k8s-calico/stacklight/server.yml
index 5635528..4e48477 100644
--- a/classes/cluster/virtual-mcp11-k8s-calico/stacklight/server.yml
+++ b/classes/cluster/virtual-mcp11-k8s-calico/stacklight/server.yml
@@ -17,6 +17,7 @@
 - system.galera.server.database.grafana
 - system.salt.minion.cert.prometheus_server
 - system.keepalived.cluster.instance.prometheus_server_vip
+- system.prometheus.server.alertmanager.dns
 - system.prometheus.server.target.etcd
 - system.prometheus.server.target.kubernetes
 - system.prometheus.server.target.dns