Fix Prometheus node/cluster labels

src/lavinmq/config.cr

@@ -50,6 +50,7 @@ module LavinMQ
     property free_disk_min : Int64 = 0  # bytes
     property free_disk_warn : Int64 = 0 # bytes
     property? clustering = false
+    property clustering_name = ""
     property clustering_etcd_prefix = "lavinmq"
     property clustering_etcd_endpoints = "localhost:2379"
     property clustering_advertised_uri : String? = nil
@@ -122,6 +123,9 @@ module LavinMQ
         p.on("--clustering", "Enable clustering") do
           @clustering = true
         end
+        p.on("--clustering-name=NAME", "Cluster name, currently only used to group Prometheus metrics (default: \"\")") do |v|
+          @clustering_name = v
+        end
         p.on("--clustering-advertised-uri=URI", "Advertised URI for the clustering server") do |v|
           @clustering_advertised_uri = v
         end
@@ -241,6 +245,7 @@ module LavinMQ
       settings.each do |config, v|
         case config
         when "enabled"              then @clustering = true?(v)
+        when "name"                 then @clustering_name = v
         when "etcd_prefix"          then @clustering_etcd_prefix = v
         when "etcd_endpoints"       then @clustering_etcd_endpoints = v
         when "advertised_uri"       then @clustering_advertised_uri = v

src/lavinmq/http/controller/prometheus.cr

@@ -134,7 +134,8 @@ module LavinMQ
                       help:   "System information",
                       labels: {
                         "#{writer.prefix}_version" => LavinMQ::VERSION,
-                        "#{writer.prefix}_cluster" => System.hostname,
+                        "#{writer.prefix}_node"    => System.hostname,
+                        "#{writer.prefix}_cluster" => Config.instance.clustering_name,
                       }})
 
         writer.write({name:  "connections_opened_total",