prometheus: Add a metrics family for Khepri's Ra counters

This exposes all of the metrics that Ra collects in counters for the
node's Khepri server under a new metric family in the "detailed"
registry.

Author: the-mikedavis

deps/rabbit/src/rabbit_khepri.erl

@@ -105,6 +105,7 @@
          nodes/0,
          locally_known_nodes/0,
          get_ra_cluster_name/0,
+         get_server_id/1,
          get_store_id/0,
          transfer_leadership/1,
 
@@ -669,6 +670,14 @@ locally_known_nodes() ->
 get_ra_cluster_name() ->
     ?RA_CLUSTER_NAME.
 
+-spec get_server_id(Node) -> RaServerId when
+      Node :: node(),
+      RaServerId :: ra:server_id().
+%% @doc Returns the Ra server id of the Khepri member on the given node.
+
+get_server_id(Node) ->
+    {?RA_CLUSTER_NAME, Node}.
+
 -spec get_store_id() -> StoreId when
       StoreId :: khepri:store_id().
 %% @doc Returns the Khepri store identifier.

deps/rabbitmq_prometheus/src/collectors/prometheus_rabbitmq_core_metrics_collector.erl

@@ -18,6 +18,8 @@
 
 -import(prometheus_text_format, [escape_label_value/1]).
 
+-include_lib("stdlib/include/assert.hrl").
+-include_lib("kernel/include/logger.hrl").
 -include_lib("rabbit_common/include/rabbit.hrl").
 
 -behaviour(prometheus_collector).
@@ -298,6 +300,12 @@ deregister_cleanup(_) -> ok.
 collect_mf('detailed', Callback) ->
     collect(true, ?DETAILED_METRIC_NAME_PREFIX, vhosts_filter_from_pdict(), enabled_mfs_from_pdict(?METRICS_RAW), Callback),
     collect(true, ?CLUSTER_METRIC_NAME_PREFIX, vhosts_filter_from_pdict(), enabled_mfs_from_pdict(?METRICS_CLUSTER), Callback),
+    case is_mf_enabled(khepri) of
+        true ->
+            collect_khepri_info(Callback);
+        false ->
+            ok
+    end,
     %% identity is here to enable filtering on a cluster name (as already happens in existing dashboards)
     emit_identity_info(Callback),
     ok;
@@ -331,6 +339,20 @@ totals(Callback) ->
      end || {Table, Name, Type, Help} <- ?TOTALS],
     ok.
 
+collect_khepri_info(Callback) ->
+    ServerId = rabbit_khepri:get_server_id(node()),
+    maps:foreach(
+      fun (Name, #{type := Type, help := Help, values := #{ServerId := Value}}) ->
+              Callback(
+                create_mf(
+                  <<?DETAILED_METRIC_NAME_PREFIX/binary,
+                    "khepri_",
+                    (prometheus_model_helpers:metric_name(Name))/binary>>,
+                  Help, Type, [Value]));
+          (_Name, _Format) ->
+                ok
+      end, seshat:format(ra)).
+
 emit_identity_info(Callback) ->
     add_metric_family(build_info(), Callback),
     add_metric_family(identity_info(), Callback),
@@ -814,12 +836,19 @@ sum('', B) ->
 sum(A, B) ->
     A + B.
 
+is_mf_enabled(MF) ->
+    case get(prometheus_mf_filter) of
+        undefined ->
+            false;
+        MFNameSet ->
+            sets:is_element(MF, MFNameSet)
+    end.
+
 enabled_mfs_from_pdict(AllMFs) ->
     case get(prometheus_mf_filter) of
         undefined ->
             [];
-        MFNames ->
-            MFNameSet = sets:from_list(MFNames),
+        MFNameSet ->
             [ MF || MF = {Table, _} <- AllMFs, sets:is_element(Table, MFNameSet) ]
     end.
 

deps/rabbitmq_prometheus/src/rabbit_prometheus_handler.erl

@@ -170,7 +170,7 @@ put_filtering_options_into_process_dictionary(Request) ->
     end,
     case parse_metric_families(Families) of
         Fs when is_list(Fs) ->
-            put(prometheus_mf_filter, Fs);
+            put(prometheus_mf_filter, sets:from_list(Fs, [{version, 2}]));
         _ -> ok
     end,
     ok.