Add autodiscovery for alertmanager

Change-Id: I253bbc96e19d379a7dc4329ea9caecd678ca481c
Depends-On: I36bdb3a4e90687d32724e5e248d5862567c36f83
diff --git a/docker/swarm/stack/monitoring.yml b/docker/swarm/stack/monitoring.yml
index 091add5..755b5d7 100644
--- a/docker/swarm/stack/monitoring.yml
+++ b/docker/swarm/stack/monitoring.yml
@@ -77,10 +77,8 @@
                 data_dir: ${_param:prometheus_server_data_directory}
                 bind_port: ${prometheus:server:bind:port}
                 bind_address: ${prometheus:server:bind:address}
-                alertmanager_port: ${prometheus:alertmanager:bind:port}
                 storage_local_engine: ${prometheus:server:storage:local:engine}
                 storage_local_retention: ${prometheus:server:storage:local:retention}
                 storage_local_memory_chunks: ${prometheus:server:storage:local:memory_chunks}
                 storage_local_max_chunks_to_persist: ${prometheus:server:storage:local:max_chunks_to_persist}
                 storage_local_num_fingerprint_mutexes: ${prometheus:server:storage:local:num_fingerprint_mutexes}
-                discovery_domain: 'monitoring_alertmanager'
diff --git a/prometheus/server/alertmanager/dns.yml b/prometheus/server/alertmanager/dns.yml
new file mode 100644
index 0000000..99fd4db
--- /dev/null
+++ b/prometheus/server/alertmanager/dns.yml
@@ -0,0 +1,12 @@
+parameters:
+  prometheus:
+    server:
+      config:
+        alertmanager:
+          docker_swarm_alertmanager:
+            enabled: true
+            dns_sd_configs:
+              domain:
+                - tasks.monitoring_alertmanager
+              type: A
+              port: ${prometheus:alertmanager:bind:port}