Add autodiscovery for alertmanager

Change-Id: I253bbc96e19d379a7dc4329ea9caecd678ca481c
Depends-On: I36bdb3a4e90687d32724e5e248d5862567c36f83
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}