Add health monitor gem (#228)

- This application does not have Honeybadger, so skipping the Honeybadger notification

Closes #213

Gemfile

@@ -90,3 +90,5 @@ group :development do
 end
 
 gem 'dockerfile-rails', '>= 1.6', group: :development
+
+gem 'health-monitor-rails', '~> 12.3'

Gemfile.lock

@@ -149,6 +149,8 @@ GEM
     fiber-storage (1.0.0)
     globalid (1.2.1)
       activesupport (>= 6.1)
+    health-monitor-rails (12.3.0)
+      railties (>= 6.1)
     i18n (1.14.5)
       concurrent-ruby (~> 1.0)
     importmap-rails (2.0.1)
@@ -390,6 +392,7 @@ GEM
 PLATFORMS
   aarch64-linux
   arm64-darwin-21
+  arm64-darwin-23
   x86_64-darwin-20
   x86_64-linux
 
@@ -406,6 +409,7 @@ DEPENDENCIES
   debug
   dockerfile-rails (>= 1.6)
   ed25519
+  health-monitor-rails (~> 12.3)
   importmap-rails
   jbuilder
   kaminari

config/initializers/health_monitor.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+Rails.application.config.after_initialize do
+  HealthMonitor.configure do |config|
+    # Make this health check available at /health
+    config.path = :health
+
+    config.error_callback = proc do |e|
+      Rails.logger.error "Health check failed with: #{e.message}"
+    end
+  end
+end

config/routes.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 Rails.application.routes.draw do
+  mount HealthMonitor::Engine, at: '/'
+
   root 'welcome#index'
   get '/welcome/index'
   get '/filing_rules', to: 'welcome#filing_rules'

spec/requests/health_check_spec.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'Health Check' do
+  describe 'GET /health' do
+    it 'has a health check' do
+      get '/health.json'
+      expect(response).to be_successful
+    end
+  end
+
+  context 'with a bad database configuration' do
+    before do
+      allow_any_instance_of(ActiveRecord::ConnectionAdapters::PostgreSQLAdapter).to receive(:execute) do |instance|
+        raise StandardError if database.blank? || instance.pool.db_config.name == database.to_s
+      end
+    end
+
+    it 'errors' do
+      get '/health.json'
+      expect(response).not_to be_successful
+      expect(response).to have_http_status :service_unavailable
+    end
+  end
+end