Re-add StatsD support through the `nsa` gem (#26310)

Gemfile

@@ -58,6 +58,7 @@ gem 'kaminari', '~> 1.2'
 gem 'link_header', '~> 0.0'
 gem 'mime-types', '~> 3.4.1', require: 'mime/types/columnar'
 gem 'nokogiri', '~> 1.15'
+gem 'nsa', github: 'jhawthorn/nsa', ref: 'e020fcc3a54d993ab45b7194d89ab720296c111b'
 gem 'oj', '~> 3.14'
 gem 'ox', '~> 2.14'
 gem 'parslet'

Gemfile.lock

@@ -7,6 +7,17 @@ GIT
       hkdf (~> 0.2)
       jwt (~> 2.0)
 
+GIT
+  remote: https://github.com/jhawthorn/nsa.git
+  revision: e020fcc3a54d993ab45b7194d89ab720296c111b
+  ref: e020fcc3a54d993ab45b7194d89ab720296c111b
+  specs:
+    nsa (0.2.8)
+      activesupport (>= 4.2, < 7.2)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      sidekiq (>= 3.5)
+      statsd-ruby (~> 1.4, >= 1.4.0)
+
 GIT
   remote: https://github.com/mastodon/rails-settings-cached.git
   revision: 86328ef0bd04ce21cc0504ff5e334591e8c2ccab
@@ -706,6 +717,7 @@ GEM
       net-scp (>= 1.1.2)
       net-ssh (>= 2.8.0)
     stackprof (0.2.25)
+    statsd-ruby (1.5.0)
     stoplight (3.0.1)
       redlock (~> 1.0)
     strong_migrations (0.8.0)
@@ -857,6 +869,7 @@ DEPENDENCIES
   net-http (~> 0.3.2)
   net-ldap (~> 0.18)
   nokogiri (~> 1.15)
+  nsa!
   oj (~> 3.14)
   omniauth (~> 1.9)
   omniauth-cas (~> 2.0)

config/initializers/statsd.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+if ENV['STATSD_ADDR'].present?
+  host, port = ENV['STATSD_ADDR'].split(':')
+
+  statsd = Statsd.new(host, port)
+  statsd.namespace = ENV.fetch('STATSD_NAMESPACE') { ['Mastodon', Rails.env].join('.') }
+
+  NSA.inform_statsd(statsd) do |informant|
+    informant.collect(:action_controller, :web)
+    informant.collect(:active_record, :db)
+    informant.collect(:active_support_cache, :cache)
+    informant.collect(:sidekiq, :sidekiq) if ENV['STATSD_SIDEKIQ'] == 'true'
+  end
+end