From e4fb16218693edd4382b96482ba94eba6c8a7f1a Mon Sep 17 00:00:00 2001
From: Kevin Lyda <kevin@ie.suberic.net>
Date: Wed, 29 Mar 2017 19:20:13 +0100
Subject: Initial pass at prometheus monitoring.

This is a step for #29118.

Add a single metric to count successful logins.

Summary types are not supported so remove Collector.  Either
we need to support the summary type or we need to create a
multiprocess-friendly Collector.

Add config to load prometheus and set up the Collector and the
Exporter.

Fix `Gemfile` as current prometheus-client gemspec is missing the
`mmap2` dependency.
---
 Gemfile.lock                           |  2 ++
 app/controllers/sessions_controller.rb |  1 +
 app/services/prom_service.rb           | 16 ++++++++++++++++
 config.ru                              |  7 +++++++
 4 files changed, 26 insertions(+)
 create mode 100644 app/services/prom_service.rb

diff --git a/Gemfile.lock b/Gemfile.lock
index 3affa434e2a..7c0f405091d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -465,6 +465,7 @@ GEM
     mimemagic (0.3.0)
     mini_portile2 (2.1.0)
     minitest (5.7.0)
+    mmap2 (2.2.6)
     mousetrap-rails (1.4.6)
     multi_json (1.12.1)
     multi_xml (0.6.0)
@@ -977,6 +978,7 @@ DEPENDENCIES
   mail_room (~> 0.9.1)
   method_source (~> 0.8)
   minitest (~> 5.7.0)
+  mmap2 (~> 2.2.6)
   mousetrap-rails (~> 1.4.6)
   mysql2 (~> 0.3.16)
   net-ssh (~> 3.0.1)
diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index 8c6ba4915cd..9870d4286a6 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -34,6 +34,7 @@ class SessionsController < Devise::SessionsController
       end
       # hide the signed-in notification
       flash[:notice] = nil
+      PromService.instance.login.increment
       log_audit_event(current_user, with: authentication_method)
       log_user_activity(current_user)
     end
diff --git a/app/services/prom_service.rb b/app/services/prom_service.rb
new file mode 100644
index 00000000000..e9ccce758e9
--- /dev/null
+++ b/app/services/prom_service.rb
@@ -0,0 +1,16 @@
+require 'prometheus/client'
+require 'singleton'
+
+class PromService
+  include Singleton
+
+  attr_reader :login
+
+  def initialize
+    @prometheus = Prometheus::Client.registry
+
+    @login = Prometheus::Client::Counter.new(:login, 'Login counter')
+    @prometheus.register(@login)
+
+  end
+end
diff --git a/config.ru b/config.ru
index 065ce59932f..82af814341b 100644
--- a/config.ru
+++ b/config.ru
@@ -13,6 +13,13 @@ if defined?(Unicorn)
     # Max memory size (RSS) per worker
     use Unicorn::WorkerKiller::Oom, min, max
   end
+
+  # TODO(lyda): Needs to be set externally.
+  ENV['prometheus_multiproc_dir'] = '/tmp'
+
+  require 'prometheus/client/rack/exporter'
+
+  use Prometheus::Client::Rack::Exporter, path: '/admin/metrics'
 end
 
 require ::File.expand_path('../config/environment',  __FILE__)
-- 
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