mod_prometheus: use 'declare' rather than 'new' for histogram and cou…

…nter (#339)

If a node crashes metrics might already be defined in prometheus and thus 'new'
would crash.

mod_prometheus/src/mod_prometheus.erl

@@ -352,7 +352,7 @@ handle_histogram(Name, HName, HistogramOpts, Host, Action, State) ->
   InitArg = State#{name => HName, labels => LabelNames},
   case Action of
     subscribe ->
-      prometheus_histogram:new(
+      prometheus_histogram:declare(
         [
           {name, HName},
           {buckets, maps:get(buckets, HistogramOpts, [1, 10, 100, 500, 750, 1000, 3000, 5000])},
@@ -377,7 +377,7 @@ handle_counter(Name, HName, CounterOpts, Host, Action, State) ->
   InitArg = State#{name => HName, labels => LabelNames},
   case Action of
     subscribe ->
-      prometheus_counter:new(
+      prometheus_counter:declare(
         [{name, HName}, {help, maps:get(help, CounterOpts, "No help")}, {labels, LabelNames}]
       ),
       ?INFO_MSG("Created new Prometheus counter for ~p with labels ~p", [HName, LabelNames]),
@@ -441,4 +441,4 @@ find_stanza_type([Arg | Args]) when is_tuple(Arg) ->
 find_stanza_type([_ | Args]) ->
   find_stanza_type(Args);
 find_stanza_type([]) ->
-  unknown.
+  unknown.