Add optional StatsD performance tracking

config/initializers/statsd.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+StatsD.prefix              = 'mastodon'
+StatsD.default_sample_rate = 1
+
+StatsDMonitor.extend(StatsD::Instrument)
+StatsDMonitor.statsd_measure(:call, 'request.duration')
+
+STATSD_REQUEST_METRICS = {
+  'request.status.success'               => 200,
+  'request.status.not_found'             => 404,
+  'request.status.too_many_requests'     => 429,
+  'request.status.internal_server_error' => 500,
+}.freeze
+
+STATSD_REQUEST_METRICS.each do |name, code|
+  StatsDMonitor.statsd_count_if(:call, name) do |status, _env, _body|
+    status.to_i == code
+  end
+end