feat(mria): Add prometheus metrics

apps/emqx_prometheus/rebar.config

@@ -3,7 +3,7 @@
 {deps,
  [ {emqx, {path, "../emqx"}},
    %% FIXME: tag this as v3.1.3
-   {prometheus, {git, "https://github.com/emqx/prometheus.erl", {ref, "9994c76adca40d91a2545102230ccce2423fd8a7"}}},
+   {prometheus, {git, "https://github.com/deadtrickster/prometheus.erl", {tag, "v4.8.1"}}},
    {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.24.0"}}},
    {minirest, {git, "https://github.com/emqx/minirest", {tag, "1.2.11"}}}
  ]}.

apps/emqx_prometheus/src/emqx_prometheus_mria.erl

@@ -0,0 +1,88 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+-module(emqx_prometheus_mria).
+
+-export([deregister_cleanup/1,
+         collect_mf/2
+        ]).
+
+-include_lib("prometheus/include/prometheus.hrl").
+
+%% Please don't remove this attribute, prometheus uses it to
+%% automatically register collectors.
+-behaviour(prometheus_collector).
+
+%%====================================================================
+%% Macros
+%%====================================================================
+
+-define(METRIC_NAME_PREFIX, "emqx_mria_").
+
+%%====================================================================
+%% Collector API
+%%====================================================================
+
+%% @private
+deregister_cleanup(_) -> ok.
+
+%% @private
+-spec collect_mf(_Registry, Callback) -> ok when
+    _Registry :: prometheus_registry:registry(),
+    Callback :: prometheus_collector:callback().
+collect_mf(_Registry, Callback) ->
+  case mria_rlog:backend() of
+      rlog ->
+          Metrics = metrics(),
+          _ = [add_metric_family(Metric, Callback) || Metric <- Metrics],
+          ok;
+      mnesia ->
+          ok
+  end.
+
+add_metric_family({Name, Metrics}, Callback) ->
+    Callback(prometheus_model_helpers:create_mf( ?METRIC_NAME(Name)
+                                               , <<"">>
+                                               , gauge
+                                               , catch_all(Metrics)
+                                               )).
+
+%%====================================================================
+%% Internal functions
+%%====================================================================
+
+metrics() ->
+    Metrics = case mria_rlog:role() of
+                  replicant ->
+                      [lag, bootstrap_time, bootstrap_num_keys, message_queue_len];
+                  core ->
+                      [last_intercepted_trans, weight, replicants, server_mql]
+              end,
+    [{MetricId, fun() -> get_shard_metric(MetricId) end} || MetricId <- Metrics].
+
+get_shard_metric(Metric) ->
+    %% TODO: only report shards that are up
+    [{[{shard, Shard}], get_shard_metric(Metric, Shard)} ||
+        Shard <- mria_schema:shards(), Shard =/= undefined].
+
+get_shard_metric(replicants, Shard) ->
+    length(mria_status:agents(Shard));
+get_shard_metric(Metric, Shard) ->
+    maps:get(Metric, mria_status:get_shard_stats(Shard), undefined).
+
+catch_all(DataFun) ->
+    try DataFun()
+    catch _:_ -> undefined
+    end.