puppet: Add rabbitmq prometheus plugin, and open the firewall.

puppet/zulip_ops/manifests/app_frontend_monitoring.pp

@@ -1,6 +1,7 @@
 # @summary Munin monitoring of a Django frontend and RabbitMQ server.
 #
 class zulip_ops::app_frontend_monitoring {
+  include zulip_ops::prometheus::rabbitmq
   include zulip_ops::prometheus::uwsgi
   include zulip_ops::munin_node
   $munin_plugins = [

puppet/zulip_ops/manifests/prometheus/rabbitmq.pp

@@ -0,0 +1,12 @@
+# @summary Prometheus monitoring of rabbitmq server.  This is done via
+# the built-in prometheus plugin which serves on port 15692:
+# https://www.rabbitmq.com/prometheus.html
+#
+class zulip_ops::prometheus::rabbitmq {
+  exec { 'enable rabbitmq-prometheus':
+    command => 'rabbitmq-plugins enable rabbitmq_prometheus',
+    unless  => 'grep -q rabbitmq_prometheus /etc/rabbitmq/enabled_plugins',
+    require => Service['rabbitmq-server'],
+  }
+  zulip_ops::firewall_allow { 'rabbitmq': port => '15692' }
+}