Make update interval configurable

lib/kafkaex_lag_exporter/consumer_offset_runner.ex

@@ -5,8 +5,6 @@ defmodule KafkaexLagExporter.ConsumerOffsetRunner do
 
   require Logger
 
-  @interval 5_000
-
   def start_link(default) when is_list(default) do
     GenServer.start_link(__MODULE__, default, name: __MODULE__)
   end
@@ -18,23 +16,29 @@ defmodule KafkaexLagExporter.ConsumerOffsetRunner do
     clients = Application.get_env(:brod, :clients)
     endpoints = clients[:kafka_client][:endpoints] || [{"redpanda", 29_092}]
 
+    interval =
+      System.get_env("KAFKA_EX_INTERVAL", "5000")
+      |> String.to_integer()
+
     Logger.info("Reveived Kafka endpoints: #{inspect(endpoints)}")
+    Logger.info("Updating lag information every #{interval} milliseconds")
 
-    Process.send_after(self(), :tick, @interval)
+    Process.send_after(self(), :tick, interval)
 
-    {:ok, %{endpoints: endpoints}}
+    {:ok, %{endpoints: endpoints, interval: interval}}
   end
 
   @impl true
   def handle_info(:tick, state) do
     [endpoint | _] = state.endpoints
+    interval = state.interval
 
     %{lags: lags, sum: lag_sum} = KafkaexLagExporter.ConsumerOffsetFetcher.get(endpoint)
 
     KafkaexLagExporter.Metrics.group_lag_per_partition(endpoint, lags)
     KafkaexLagExporter.Metrics.group_sum_lag(endpoint, lag_sum)
 
-    Process.send_after(self(), :tick, @interval)
+    Process.send_after(self(), :tick, interval)
 
     {:noreply, state}
   end