add the configuration for health-monitor

we initialize health-monitor and configure it

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 removed from 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'

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)
+    end
+  end
+end