Add prometheus relay service

Set 2 replicas for prometheus server

Change-Id: I859195d5504d61511830899f2c28c92e24219585
diff --git a/docker/swarm/stack/monitoring/init.yml b/docker/swarm/stack/monitoring/init.yml
index 95f5f8d..e274426 100644
--- a/docker/swarm/stack/monitoring/init.yml
+++ b/docker/swarm/stack/monitoring/init.yml
@@ -15,6 +15,22 @@
               driver_opts:
                 encrypted: 1
           service:
+            relay:
+              networks:
+                - monitoring
+              deploy:
+                replicas: 2
+                labels:
+                  com.mirantis.monitoring: "relay"
+                restart_policy:
+                  condition: any
+              labels:
+                com.mirantis.monitoring: "relay"
+              image: ${_param:docker_image_prometheus_relay}
+              ports:
+                - 15016:8080
+              environment:
+                PROMETHEUS_RELAY_DNS: 'tasks.monitoring_server'
             remote_storage_adapter:
               networks:
                 - monitoring
@@ -81,7 +97,7 @@
               networks:
                 - monitoring
               deploy:
-                replicas: 1
+                replicas: 2
                 labels:
                   com.mirantis.monitoring: "prometheus"
                 restart_policy: