Add prometheus_exporter gem and instrumentation to the project

Gemfile

@@ -6,6 +6,7 @@ git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 ruby File.read('.ruby-version').strip
 
 gem 'bootsnap', require: false
+gem 'prometheus_exporter'
 gem 'chartkick'
 gem 'data_migrate'
 gem 'devise'

Gemfile.lock

@@ -233,6 +233,8 @@ GEM
     patience_diff (1.2.0)
       optimist (~> 3.0)
     pg (1.5.9)
+    prometheus_exporter (2.1.1)
+      webrick
     pry (0.14.2)
       coderay (~> 1.1)
       method_source (~> 1.0)
@@ -408,6 +410,7 @@ GEM
       addressable (>= 2.8.0)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)
+    webrick (1.9.0)
     websocket-driver (0.7.6)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
@@ -441,6 +444,7 @@ DEPENDENCIES
   lograge
   oj
   pg
+  prometheus_exporter
   pry-byebug
   pry-rails
   puma

config/initializers/prometheus.rb

@@ -0,0 +1,15 @@
+# in config/initializers/prometheus.rb
+if Rails.env != "test"
+  require 'prometheus_exporter/middleware'
+
+  # This reports stats per request like HTTP status and timings
+  Rails.application.middleware.unshift PrometheusExporter::Middleware
+end
+
+if Rails.env != "test"
+  require 'prometheus_exporter/instrumentation'
+
+  # this reports basic process stats like RSS and GC info, type master
+  # means it is instrumenting the master process
+  PrometheusExporter::Instrumentation::Process.start(type: "master")
+end

config/initializers/sidekiq.rb

@@ -2,6 +2,11 @@
 
 Sidekiq.configure_server do |config|
   config.redis = { url: ENV['REDIS_URL'] }
+
+  config.server_middleware do |chain|
+    require 'prometheus_exporter/instrumentation'
+    chain.add PrometheusExporter::Instrumentation::Sidekiq
+ end
 end
 
 Sidekiq.configure_client do |config|

config/puma.rb

@@ -41,3 +41,9 @@ pidfile ENV.fetch("PIDFILE") { "tmp/pids/server.pid" }
 
 # Allow puma to be restarted by `bin/rails restart` command.
 plugin :tmp_restart
+
+# in unicorn/puma/passenger be sure to run a new process instrumenter after fork
+after_worker_boot do
+  require 'prometheus_exporter/instrumentation'
+  PrometheusExporter::Instrumentation::Process.start(type:"web")
+end