Add (optional) Sentry integration

A Sentry DSN can be set via `SENTRY_DSN` and authenticated users will be
tagged with ID and username (cn) in events.

Gemfile

@@ -48,6 +48,10 @@ gem 'faraday'
 gem 'sidekiq', '< 7'
 gem 'sidekiq-scheduler'
 
+# Monitoring
+gem "sentry-ruby"
+gem "sentry-rails"
+
 group :development, :test do
   # Use sqlite3 as the database for Active Record
   gem 'sqlite3', '~> 1.4'

Gemfile.lock

@@ -254,6 +254,11 @@ GEM
     ruby2_keywords (0.0.5)
     rufus-scheduler (3.8.2)
       fugit (~> 1.1, >= 1.1.6)
+    sentry-rails (5.8.0)
+      railties (>= 5.0)
+      sentry-ruby (~> 5.8.0)
+    sentry-ruby (5.8.0)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
     sidekiq (6.5.5)
       connection_pool (>= 2.2.2)
       rack (~> 2.0)
@@ -335,6 +340,8 @@ DEPENDENCIES
   rails-settings-cached (~> 2.8.3)
   rqrcode (~> 2.0)
   rspec-rails
+  sentry-rails
+  sentry-ruby
   sidekiq (< 7)
   sidekiq-scheduler
   sprockets-rails

app/controllers/application_controller.rb

@@ -3,6 +3,18 @@ class ApplicationController < ActionController::Base
     render :text => exception, :status => 500
   end
 
+  before_action :sentry_set_user
+
+  def sentry_set_user
+    return unless Setting.sentry_enabled
+
+    if user_signed_in?
+      Sentry.set_user(id: current_user.id, username: current_user.cn)
+    else
+      Sentry.set_user({})
+    end
+  end
+
   def require_user_signed_in
     unless user_signed_in?
       redirect_to welcome_path and return

app/models/setting.rb

@@ -10,6 +10,13 @@ class Setting < RailsSettings::Base
     account accounts donations mail webmaster support
   ]
 
+  #
+  # Sentry
+  #
+
+  field :sentry_enabled, type: :boolean, readonly: true,
+    default: (ENV["SENTRY_DSN"].present?.to_s || false)
+
   #
   # Discourse
   #

config/initializers/sentry.rb

@@ -0,0 +1,9 @@
+if ENV["SENTRY_DSN"].present?
+  Sentry.init do |config|
+    config.dsn = ENV["SENTRY_DSN"]
+    config.breadcrumbs_logger = [:active_support_logger, :http_logger]
+    config.traces_sampler = lambda do |context|
+      true
+    end
+  end
+end

config/routes.rb

@@ -1,7 +1,7 @@
 require 'sidekiq/web'
 
 Rails.application.routes.draw do
-  devise_for :users, :controllers => { :confirmations => "users/confirmations" }
+  devise_for :users, controllers: { confirmations: "users/confirmations" }
 
   get 'welcome', to: 'welcome#index'
   get 'check_your_email', to: 'welcome#check_your_email'