Add metrics stub

lib/kafkaex_lag_exporter/consumer_offset_fetcher.ex

@@ -8,7 +8,7 @@ defmodule KafkaexLagExporter.ConsumerOffsetFetcher do
   @interval 5_000
 
   def start_link(default) when is_list(default) do
-    GenServer.start_link(__MODULE__, default)
+    GenServer.start_link(__MODULE__, default, name: __MODULE__)
   end
 
   @impl true
@@ -34,7 +34,7 @@ defmodule KafkaexLagExporter.ConsumerOffsetFetcher do
       :brod.describe_groups(endpoint, [], consumer_group_names)
       |> get_consumer_lags
 
-    Logger.info("Consumer lags: #{inspect(consumer_lags)}")
+    KafkaexLagExporter.Metrics.kafka_metrics(endpoint, consumer_lags)
 
     Process.send_after(self(), :tick, @interval)
 
@@ -57,6 +57,9 @@ defmodule KafkaexLagExporter.ConsumerOffsetFetcher do
     |> Enum.map(fn [consumer_group, members] -> [consumer_group, get_topic_names(members)] end)
     |> Enum.map(fn [consumer_group, topics] ->
       [consumer_group, get_lag_for_consumer(consumer_group, topics)]
+
+      # credo:disable-for-next-line
+      # TODO: [consumer_group, topic, get_lag_for_consumer(consumer_group, topic)]
     end)
   end
 

lib/kafkaex_lag_exporter/metrics.ex

@@ -0,0 +1,46 @@
+defmodule KafkaexLagExporter.Metrics do
+  @moduledoc "Metrics module is responsible for building and collecting kafka metrics"
+
+  use PromEx.Plugin
+
+  require Logger
+
+  @kafka_event :kafka
+
+  @impl true
+  def manual_metrics(_opts) do
+    clients = Application.get_env(:brod, :clients)
+    [endpoint | _] = clients[:kafka_client][:endpoints] || [{"redpanda", 29_092}]
+
+    Manual.build(
+      :application_versions_manual_metrics,
+      {__MODULE__, :kafka_metrics, [endpoint, []]},
+      [
+        last_value(
+          [@kafka_event, :consumergroup, :group, :topic, :sum, :lag],
+          event_name: [@kafka_event, :consumergroup, :group, :topic, :sum, :lag],
+          description: "Sum of group offset lag across topic partitions",
+          measurement: :lag,
+          tags: [:cluster_name, :group, :topic]
+        )
+      ]
+    )
+  end
+
+  @doc false
+  def kafka_metrics({host, _port}, consumer_lags) do
+    Enum.each(consumer_lags, fn [group_name, lag] ->
+      :telemetry.execute(
+        [@kafka_event, :consumergroup, :group, :topic, :sum, :lag],
+        %{
+          lag: lag
+        },
+        %{
+          cluster_name: host,
+          group: group_name,
+          topic: []
+        }
+      )
+    end)
+  end
+end

lib/kafkaex_lag_exporter/prom_ex.ex

@@ -61,7 +61,7 @@ defmodule KafkaexLagExporter.PromEx do
     [
       # PromEx built in plugins
       Plugins.Application,
-      Plugins.Beam
+      Plugins.Beam,
       # {Plugins.Phoenix, router: KafkaexLagExporterWeb.Router, endpoint: KafkaexLagExporterWeb.Endpoint},
       # Plugins.Ecto,
       # Plugins.Oban,
@@ -70,7 +70,7 @@ defmodule KafkaexLagExporter.PromEx do
       # Plugins.Broadway,
 
       # Add your own PromEx metrics plugins
-      # KafkaexLagExporter.Users.PromExPlugin
+      KafkaexLagExporter.Metrics
     ]
   end
 end