loadbalancer cap tasks (#1206)

* add the health monitor gem

we use this to monitor the health of an application

* add the configuration for health-monitor

we initialize health-monitor and configure it

* Update config/deploy.rb

Co-authored-by: Max Kadel <mkadel@princeton.edu>

* Update config/initializers/health_monitor.rb

Co-authored-by: Max Kadel <mkadel@princeton.edu>

---------

Co-authored-by: Max Kadel <mkadel@princeton.edu>

Gemfile

@@ -42,6 +42,9 @@ gem "kaminari"
 # static pages
 gem "high_voltage"
 
+# health monitor
+gem "health-monitor-rails", "12.4.0"
+
 gem "honeybadger"
 
 group :development, :test do

Gemfile.lock

@@ -152,6 +152,8 @@ GEM
     globalid (1.2.1)
       activesupport (>= 6.1)
     hashie (5.0.0)
+    health-monitor-rails (12.4.0)
+      railties (>= 6.1)
     high_voltage (4.0.0)
     honeybadger (5.15.5)
     i18n (1.14.6)
@@ -420,6 +422,7 @@ DEPENDENCIES
   ed25519
   factory_bot_rails
   faker
+  health-monitor-rails (= 12.4.0)
   high_voltage
   honeybadger
   jbuilder

config/deploy.rb

@@ -157,6 +157,36 @@
 
   after :finishing, 'deploy:cleanup'
 
+  #   # You can/ should apply this command to a subset of hosts
+# cap --hosts=lib-approvals-staging2.lib.princeton.edu staging application:remove_from_nginx
+desc "Marks the server(s) to be removed from the loadbalancer"
+  task :remove_from_nginx do
+    count = 0
+    on roles(:app) do
+      count += 1
+    end
+    if count > (roles(:app).length / 2)
+      raise "You must run this command on individual servers utilizing the --hosts= switch"
+    end
+    on roles(:app) do
+      within release_path do
+        execute :touch, "public/remove-from-nginx"
+      end
+    end
+  end
+ # You can/ should apply this command to a subset of hosts
+  # cap --hosts=lib-approvals-staging2.lib.princeton.edu staging application:serve_from_nginx
+  desc "Marks the server(s) to be added back to the loadbalancer"
+  task :serve_from_nginx do
+    on roles(:app) do
+      within release_path do
+        execute :rm, "-f public/remove-from-nginx"
+      end
+    end
+  end
+end
+
+# before "deploy:reverted", "deploy:assets:precompile"
   # # We shouldn't need this because it should be built in to Rails 5.1
   # # see https://github.com/rails/webpacker/issues/1037
   # desc 'Run yarn install'
@@ -168,4 +198,4 @@
   #   end
   # end
   # before "deploy:assets:precompile", "deploy:yarn_install"
-end
+# end

config/initializers/health_monitor.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+Rails.application.config.after_initialize do
+  HealthMonitor.configure do |config|
+    config.cache
+
+    config.path = :health
+
+    config.file_absence.configure do |file_config|
+      file_config.filename = "public/remove-from-nginx"
+    end
+
+    config.error_callback = proc do |e|
+      Rails.logger.error "Health check failed with: #{e.message}"
+      Honeybadger.notify(e) unless e.is_a(HealthMonitor::Providers::FileAbsenceException)
+    end
+  end
+end