diff --git a/lessons/220/rails-app/.gitignore b/lessons/220/rails-app/.gitignore
index 5ba3862bb..8cf556f84 100644
--- a/lessons/220/rails-app/.gitignore
+++ b/lessons/220/rails-app/.gitignore
@@ -31,3 +31,5 @@
 
 # Ignore master key for decrypting credentials and more.
 /config/master.key
+
+/.idea
diff --git a/lessons/220/rails-app/Dockerfile b/lessons/220/rails-app/Dockerfile
index 6370ff492..f3d6601bd 100644
--- a/lessons/220/rails-app/Dockerfile
+++ b/lessons/220/rails-app/Dockerfile
@@ -60,4 +60,4 @@ ENTRYPOINT ["/rails/bin/docker-entrypoint"]
 
 # Start the server by default, this can be overwritten at runtime
 EXPOSE 8080
-CMD ["./bin/rails", "server"]
+CMD ["./bin/rails", "server", "-b", "0.0.0.0", "-p", "8080"]
diff --git a/lessons/220/rails-app/Gemfile b/lessons/220/rails-app/Gemfile
index 673845cb9..f622fb28d 100644
--- a/lessons/220/rails-app/Gemfile
+++ b/lessons/220/rails-app/Gemfile
@@ -1,47 +1,12 @@
 source "https://rubygems.org"
 
-gem 'pg'
+gem "falcon"
+gem "oj"
+gem "pg"
+gem "prometheus-client"
+gem "rage-rb"
 
-gem 'prometheus-client'
-
-# Bundle edge Rails instead: gem "rails", github: "rails/rails", branch: "main"
-gem "rails", "~> 7.2.1", ">= 7.2.1.2"
-# Use sqlite3 as the database for Active Record
-gem "sqlite3", ">= 1.4"
-# Use the Puma web server [https://github.com/puma/puma]
-gem "puma", ">= 5.0"
-# Build JSON APIs with ease [https://github.com/rails/jbuilder]
-# gem "jbuilder"
-# Use Redis adapter to run Action Cable in production
-# gem "redis", ">= 4.0.1"
-
-# Use Kredis to get higher-level data types in Redis [https://github.com/rails/kredis]
-# gem "kredis"
-
-# Use Active Model has_secure_password [https://guides.rubyonrails.org/active_model_basics.html#securepassword]
-# gem "bcrypt", "~> 3.1.7"
-
-# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
-gem "tzinfo-data", platforms: %i[ windows jruby ]
+gem "rails"
 
 # Reduces boot times through caching; required in config/boot.rb
 gem "bootsnap", require: false
-
-# Use Active Storage variants [https://guides.rubyonrails.org/active_storage_overview.html#transforming-images]
-# gem "image_processing", "~> 1.2"
-
-# Use Rack CORS for handling Cross-Origin Resource Sharing (CORS), making cross-origin Ajax possible
-# gem "rack-cors"
-
-group :development, :test do
-  # See https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debug-gem
-  gem "debug", platforms: %i[ mri windows ], require: "debug/prelude"
-
-  # Static analysis for security vulnerabilities [https://brakemanscanner.org/]
-  gem "brakeman", require: false
-
-  # Omakase Ruby styling [https://github.com/rails/rubocop-rails-omakase/]
-  gem "rubocop-rails-omakase", require: false
-end
-
-
diff --git a/lessons/220/rails-app/app/channels/application_cable/channel.rb b/lessons/220/rails-app/app/channels/application_cable/channel.rb
deleted file mode 100644
index d67269728..000000000
--- a/lessons/220/rails-app/app/channels/application_cable/channel.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-module ApplicationCable
-  class Channel < ActionCable::Channel::Base
-  end
-end
diff --git a/lessons/220/rails-app/app/channels/application_cable/connection.rb b/lessons/220/rails-app/app/channels/application_cable/connection.rb
deleted file mode 100644
index 0ff5442f4..000000000
--- a/lessons/220/rails-app/app/channels/application_cable/connection.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-module ApplicationCable
-  class Connection < ActionCable::Connection::Base
-  end
-end
diff --git a/lessons/220/rails-app/app/controllers/application_controller.rb b/lessons/220/rails-app/app/controllers/application_controller.rb
index 4ac8823b0..3425a35ce 100644
--- a/lessons/220/rails-app/app/controllers/application_controller.rb
+++ b/lessons/220/rails-app/app/controllers/application_controller.rb
@@ -1,2 +1,2 @@
-class ApplicationController < ActionController::API
+class ApplicationController < ActionController::Metal
 end
diff --git a/lessons/220/rails-app/app/controllers/devices_controller.rb b/lessons/220/rails-app/app/controllers/devices_controller.rb
index 01aa9fdf3..edc6e89ac 100644
--- a/lessons/220/rails-app/app/controllers/devices_controller.rb
+++ b/lessons/220/rails-app/app/controllers/devices_controller.rb
@@ -1,56 +1,34 @@
-class DevicesController < ApplicationController
-  before_action :set_device, only: %i[ show update destroy ]
+# frozen_string_literal: true
 
+class DevicesController < ApplicationController
   # GET /devices
   def index
     devices = [
-      Device.new(id: 1, uuid: "9add349c-c35c-4d32-ab0f-53da1ba40a2a", mac: "5F-33-CC-1F-43-82", firmware: "2.1.6", created_at: "2024-5-28T15:21:51.137Z", updated_at: "2024-5-28T15:21:51.137Z"),
-      Device.new(id: 2, uuid: "d2293412-36eb-46e7-9231-af7e9249fffe", mac: "E7-34-96-33-0C-4C", firmware: "1.0.3", created_at: "2024-01-28T15:20:51.137Z", updated_at: "2024-01-28T15:20:51.137Z"),
-      Device.new(id: 3, uuid: "eee58ca8-ca51-47a5-ab48-163fd0e44b77", mac: "68-93-9B-B5-33-B9", firmware: "4.3.1", created_at: "2024-8-28T15:18:21.137Z", updated_at: "2024-8-28T15:18:21.137Z")
+      Device.new(id: 1, uuid: "9add349c-c35c-4d32-ab0f-53da1ba40a2a", mac: "5F-33-CC-1F-43-82", firmware: "2.1.6", created_at: "2024-5-28T15:21:51.137Z", updated_at: "2024-5-28T15:21:51.137Z").attributes,
+      Device.new(id: 2, uuid: "d2293412-36eb-46e7-9231-af7e9249fffe", mac: "E7-34-96-33-0C-4C", firmware: "1.0.3", created_at: "2024-01-28T15:20:51.137Z", updated_at: "2024-01-28T15:20:51.137Z").attributes,
+      Device.new(id: 3, uuid: "eee58ca8-ca51-47a5-ab48-163fd0e44b77", mac: "68-93-9B-B5-33-B9", firmware: "4.3.1", created_at: "2024-8-28T15:18:21.137Z", updated_at: "2024-8-28T15:18:21.137Z").attributes
     ]
-    
-    render json: devices
-  end
 
-  # GET /devices/1
-  def show
-    render json: @device
+    build_response(devices, 200)
   end
 
   # POST /devices
   def create
-    @device = Device.new(device_params)
-    @device.uuid = SecureRandom.uuid
-
-    if @device.save
-      render json: @device, status: :created, location: @device
-    else
-      render json: @device.errors, status: :unprocessable_entity
-    end
-  end
+    device = Device.new(params.slice(:mac, :firmware))
+    device.uuid = SecureRandom.uuid
 
-  # PATCH/PUT /devices/1
-  def update
-    if @device.update(device_params)
-      render json: @device
+    if device.save
+      build_response(device, 201)
     else
-      render json: @device.errors, status: :unprocessable_entity
+      build_response(device.errors, 422)
     end
   end
 
-  # DELETE /devices/1
-  def destroy
-    @device.destroy!
-  end
-
   private
-    # Use callbacks to share common setup or constraints between actions.
-    def set_device
-      @device = Device.find(params[:id])
-    end
 
-    # Only allow a list of trusted parameters through.
-    def device_params
-      params.require(:device).permit(:uuid, :mac, :firmware)
-    end
+  def build_response(body, status_code)
+    self.content_type = "application/json"
+    self.status = status_code
+    self.response_body = body.to_json
+  end
 end
diff --git a/lessons/220/rails-app/app/jobs/application_job.rb b/lessons/220/rails-app/app/jobs/application_job.rb
deleted file mode 100644
index d394c3d10..000000000
--- a/lessons/220/rails-app/app/jobs/application_job.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-class ApplicationJob < ActiveJob::Base
-  # Automatically retry jobs that encountered a deadlock
-  # retry_on ActiveRecord::Deadlocked
-
-  # Most jobs are safe to ignore if the underlying records are no longer available
-  # discard_on ActiveJob::DeserializationError
-end
diff --git a/lessons/220/rails-app/app/mailers/application_mailer.rb b/lessons/220/rails-app/app/mailers/application_mailer.rb
deleted file mode 100644
index 3c34c8148..000000000
--- a/lessons/220/rails-app/app/mailers/application_mailer.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-class ApplicationMailer < ActionMailer::Base
-  default from: "from@example.com"
-  layout "mailer"
-end
diff --git a/lessons/220/rails-app/app/models/device.rb b/lessons/220/rails-app/app/models/device.rb
index c0b432e61..e9442ae21 100644
--- a/lessons/220/rails-app/app/models/device.rb
+++ b/lessons/220/rails-app/app/models/device.rb
@@ -1,2 +1,9 @@
 class Device < ApplicationRecord
+  def save
+    result = nil
+
+    PrometheusClient.db_histogram.observe(Benchmark.realtime { result = super })
+
+    result
+  end
 end
diff --git a/lessons/220/rails-app/app/subscribers/active_record_prometheus_subscriber.rb b/lessons/220/rails-app/app/subscribers/active_record_prometheus_subscriber.rb
deleted file mode 100644
index b7e0cced3..000000000
--- a/lessons/220/rails-app/app/subscribers/active_record_prometheus_subscriber.rb
+++ /dev/null
@@ -1,70 +0,0 @@
-require 'prometheus/client'
-
-class Prom
-  include Singleton
-
-  def client
-    @client ||= Prometheus::Client.registry
-  end
-
-  def self.histograms(*args)
-    instance.histograms(*args)
-  end
-
-  def histograms
-    @histograms ||= Hash.new do |hash, key|
-      hash[key] = client.histogram(:myapp_request_duration_seconds, docstring: 'Duration of the request.', labels: [:op], buckets: buckets)
-    end
-  end
-
-  private
-  def buckets
-    # Unlike a Summary, buckets must be defined based on the expected application latency to capture as many distributions as possible.
-    # More buckets mean more load on your monitoring system, so adapt to your app!!!
-    hist_buckets = [
-      0.00001, 0.000015, 0.00002, 0.000025, 0.00003, 0.000035, 0.00004, 0.000045,
-      0.00005, 0.000055, 0.00006, 0.000065, 0.00007, 0.000075, 0.00008, 0.000085,
-      0.00009, 0.000095, 0.0001, 0.000101, 0.000102, 0.000103, 0.000104, 0.000105,
-      0.000106, 0.000107, 0.000108, 0.000109, 0.00011, 0.000111, 0.000112, 0.000113,
-      0.000114, 0.000115, 0.000116, 0.000117, 0.000118, 0.000119, 0.00012, 0.000121,
-      0.000122, 0.000123, 0.000124, 0.000125, 0.000126, 0.000127, 0.000128,
-      0.000129, 0.00013, 0.000131, 0.000132, 0.000133, 0.000134, 0.000135, 0.000136,
-      0.000137, 0.000138, 0.000139, 0.00014, 0.000141, 0.000142, 0.000143, 0.000144,
-      0.000145, 0.000146, 0.000147, 0.000148, 0.000149, 0.00015, 0.000151, 0.000152,
-      0.000153, 0.000154, 0.000155, 0.000156, 0.000157, 0.000158, 0.000159, 0.00016,
-      0.000161, 0.000162, 0.000163, 0.000164, 0.000165, 0.000166, 0.000167,
-      0.000168, 0.000169, 0.00017, 0.000171, 0.000172, 0.000173, 0.000174, 0.000175,
-      0.000176, 0.000177, 0.000178, 0.000179, 0.00018, 0.000181, 0.000182, 0.000183,
-      0.000184, 0.000185, 0.000186, 0.000187, 0.000188, 0.000189, 0.00019, 0.000191,
-      0.000192, 0.000193, 0.000194, 0.000195, 0.000196, 0.000197, 0.000198,
-      0.000199, 0.0002, 0.00021, 0.00022, 0.00023, 0.00024, 0.00025, 0.00026,
-      0.00027, 0.00028, 0.00029, 0.0003, 0.00031, 0.00032, 0.00033, 0.00034,
-      0.00035, 0.00036, 0.00037, 0.00038, 0.00039, 0.0004, 0.00041, 0.00042,
-      0.00043, 0.00044, 0.00045, 0.00046, 0.00047, 0.00048, 0.00049, 0.0005,
-      0.00051, 0.00052, 0.00053, 0.00054, 0.00055, 0.00056, 0.00057, 0.00058,
-      0.00059, 0.0006, 0.00061, 0.00062, 0.00063, 0.00064, 0.00065, 0.00066,
-      0.00067, 0.00068, 0.00069, 0.0007, 0.00071, 0.00072, 0.00073, 0.00074,
-      0.00075, 0.00076, 0.00077, 0.00078, 0.00079, 0.0008, 0.00081, 0.00082,
-      0.00083, 0.00084, 0.00085, 0.00086, 0.00087, 0.00088, 0.00089, 0.0009,
-      0.00091, 0.00092, 0.00093, 0.00094, 0.00095, 0.00096, 0.00097, 0.00098,
-      0.00099, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005,
-      0.0055, 0.006, 0.0065, 0.007, 0.0075, 0.008, 0.0085, 0.009, 0.0095, 0.01,
-      0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07,
-      0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45,
-      0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.5, 2.0, 2.5,
-      3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0,
-      10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5
-    ]
-  end
-  
-end
-
-class ActiveRecordPrometheusSubscriber < ActiveSupport::Subscriber
-    attach_to :active_record
-
-    def sql(event)
-        if event.payload[:name] == "Device Create"
-            Prom.histograms['device'].observe(event.duration, labels: { op: 'db' })
-        end
-    end
-  end
diff --git a/lessons/220/rails-app/app/views/layouts/mailer.html.erb b/lessons/220/rails-app/app/views/layouts/mailer.html.erb
deleted file mode 100644
index 3aac9002e..000000000
--- a/lessons/220/rails-app/app/views/layouts/mailer.html.erb
+++ /dev/null
@@ -1,13 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <head>
-    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
-    <style>
-      /* Email styles need to be inline */
-    </style>
-  </head>
-
-  <body>
-    <%= yield %>
-  </body>
-</html>
diff --git a/lessons/220/rails-app/app/views/layouts/mailer.text.erb b/lessons/220/rails-app/app/views/layouts/mailer.text.erb
deleted file mode 100644
index 37f0bddbd..000000000
--- a/lessons/220/rails-app/app/views/layouts/mailer.text.erb
+++ /dev/null
@@ -1 +0,0 @@
-<%= yield %>
diff --git a/lessons/220/rails-app/bin/iodine b/lessons/220/rails-app/bin/iodine
new file mode 100755
index 000000000..444451211
--- /dev/null
+++ b/lessons/220/rails-app/bin/iodine
@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+#
+# This file was generated by Bundler.
+#
+# The application 'iodine' is installed as part of a gem, and
+# this file is here to facilitate running it.
+#
+
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
+
+bundle_binstub = File.expand_path("bundle", __dir__)
+
+if File.file?(bundle_binstub)
+  if File.read(bundle_binstub, 300).include?("This file was generated by Bundler")
+    load(bundle_binstub)
+  else
+    abort("Your `bin/bundle` was not generated by Bundler, so this binstub cannot run.
+Replace `bin/bundle` by running `bundle binstubs bundler --force`, then run this command again.")
+  end
+end
+
+require "rubygems"
+require "bundler/setup"
+
+load Gem.bin_path("rage-iodine", "iodine")
diff --git a/lessons/220/rails-app/config.ru b/lessons/220/rails-app/config.ru
index bb17d54e3..6ff717108 100644
--- a/lessons/220/rails-app/config.ru
+++ b/lessons/220/rails-app/config.ru
@@ -1,14 +1,9 @@
 # This file is used by Rack-based servers to start the application.
 require 'rack'
-require 'prometheus/middleware/collector'
 require 'prometheus/middleware/exporter'
 
-use Rack::Deflater
-use Prometheus::Middleware::Collector
 use Prometheus::Middleware::Exporter
 
-run ->(_) { [200, {'content-type' => 'text/html'}, ['OK']] }
-
 require_relative "config/environment"
 
 run Rails.application
diff --git a/lessons/220/rails-app/config/application.rb b/lessons/220/rails-app/config/application.rb
index a262a0041..03594b281 100644
--- a/lessons/220/rails-app/config/application.rb
+++ b/lessons/220/rails-app/config/application.rb
@@ -1,6 +1,7 @@
 require_relative "boot"
 
-require "rails/all"
+require "active_record/railtie"
+require "action_controller/railtie"
 
 # Require the gems listed in Gemfile, including any gems
 # you've limited to :test, :development, or :production.
@@ -28,5 +29,33 @@ class Application < Rails::Application
     # Middleware like session, flash, cookies can be added back manually.
     # Skip views, helpers and assets when generating a new resource.
     config.api_only = true
+    config.secret_key_base = 'secret'
+
+    config.middleware.delete Rack::Sendfile
+    config.middleware.delete ActionDispatch::Static
+    config.middleware.delete ActionDispatch::Executor
+    config.middleware.delete Rack::Runtime
+    config.middleware.delete ActionDispatch::RequestId
+    config.middleware.delete ActionDispatch::RemoteIp
+    config.middleware.delete Rails::Rack::Logger
+    config.middleware.delete ActionDispatch::ShowExceptions
+    config.middleware.delete ActionDispatch::DebugExceptions
+    config.middleware.delete ActionDispatch::Callbacks
+    config.middleware.delete Rack::Head
+    config.middleware.delete Rack::ConditionalGet
+    config.middleware.delete Rack::ETag
+
+    require 'rage/fiber'
+    require 'rage/fiber_scheduler'
+    require 'rage/middleware/fiber_wrapper'
+    config.middleware.use Rage::FiberWrapper
+
+    Oj.default_options = { mode: :compat }
+    Oj.optimize_rails
+
+    Iodine.workers = ENV.fetch('WORKERS_NUM', 2).to_i
+    Iodine.threads = 1
+
+    Iodine.on_state(:after_fork) { RubyVM::YJIT.enable }
   end
 end
diff --git a/lessons/220/rails-app/config/cable.yml b/lessons/220/rails-app/config/cable.yml
deleted file mode 100644
index a75d25a12..000000000
--- a/lessons/220/rails-app/config/cable.yml
+++ /dev/null
@@ -1,10 +0,0 @@
-development:
-  adapter: async
-
-test:
-  adapter: test
-
-production:
-  adapter: redis
-  url: <%= ENV.fetch("REDIS_URL") { "redis://localhost:6379/1" } %>
-  channel_prefix: my_rails_production
diff --git a/lessons/220/rails-app/config/credentials.yml.enc b/lessons/220/rails-app/config/credentials.yml.enc
deleted file mode 100644
index 76ee6f006..000000000
--- a/lessons/220/rails-app/config/credentials.yml.enc
+++ /dev/null
@@ -1 +0,0 @@
-e2CALB2bWwUeqUwX8KgQZbaunuG6eQBw6htvcl7MG+0eud9NW5zt1Yn52o+c7xpYB3JjGRfecJO1vt6suEUAdP7mTdB0tuo/6Hwfg7veyZbU7xbvjrKvKzVkiaCti1uiL9w5co/zgUQukf6808Y0GDRRcinYlx9zuHpxjS/0wflwHWGVK8UOinfu249e0SBPR9WfgkMi91C935l4LC8m8BC5DqyHremNwaBPkJzRGGPI5KooVnXsLwdllmNpYNeNwfGv8HaQbtvVnuEm88st1UbSPtEramxM59ufJPPVmAtu5xXgl3IFKxB7+LKzfE6qP2LInpRnZRzOk2wCTavPBHOca+8g/i7LtPfAlBLR9UzXyJy5byCnQst54wY+/sCG3kk3ouBVpfnHitJs5cXumTUkX0pT--qEXMV/EqYowkdupm--pokWm+k9iVzm7qjhSmpgbw==
\ No newline at end of file
diff --git a/lessons/220/rails-app/config/environments/development.rb b/lessons/220/rails-app/config/environments/development.rb
index 98128ff29..d2efb0e31 100644
--- a/lessons/220/rails-app/config/environments/development.rb
+++ b/lessons/220/rails-app/config/environments/development.rb
@@ -29,16 +29,16 @@
   end
 
   # Store uploaded files on the local file system (see config/storage.yml for options).
-  config.active_storage.service = :local
+  # config.active_storage.service = :local
 
   # Don't care if the mailer can't send.
-  config.action_mailer.raise_delivery_errors = false
+  # config.action_mailer.raise_delivery_errors = false
 
   # Disable caching for Action Mailer templates even if Action Controller
   # caching is enabled.
-  config.action_mailer.perform_caching = false
+  # config.action_mailer.perform_caching = false
 
-  config.action_mailer.default_url_options = { host: "localhost", port: 3000 }
+  # config.action_mailer.default_url_options = { host: "localhost", port: 3000 }
 
   # Print deprecation notices to the Rails logger.
   config.active_support.deprecation = :log
@@ -56,7 +56,7 @@
   config.active_record.verbose_query_logs = true
 
   # Highlight code that enqueued background job in logs.
-  config.active_job.verbose_enqueue_logs = true
+  # config.active_job.verbose_enqueue_logs = true
 
   # Raises error for missing translations.
   # config.i18n.raise_on_missing_translations = true
diff --git a/lessons/220/rails-app/config/environments/production.rb b/lessons/220/rails-app/config/environments/production.rb
index e7702059a..1f24c38a6 100644
--- a/lessons/220/rails-app/config/environments/production.rb
+++ b/lessons/220/rails-app/config/environments/production.rb
@@ -30,7 +30,7 @@
   # config.action_dispatch.x_sendfile_header = "X-Accel-Redirect" # for NGINX
 
   # Store uploaded files on the local file system (see config/storage.yml for options).
-  config.active_storage.service = :local
+  # config.active_storage.service = :local
 
   # Mount Action Cable outside main process or domain.
   # config.action_cable.mount_path = nil
@@ -69,7 +69,7 @@
 
   # Disable caching for Action Mailer templates even if Action Controller
   # caching is enabled.
-  config.action_mailer.perform_caching = false
+  # config.action_mailer.perform_caching = false
 
   # Ignore bad email addresses and do not raise email delivery errors.
   # Set this to true and configure the email server for immediate delivery to raise delivery errors.
diff --git a/lessons/220/rails-app/config/initializers/load_notification_subscribers.rb b/lessons/220/rails-app/config/initializers/load_notification_subscribers.rb
deleted file mode 100644
index 9e12b2497..000000000
--- a/lessons/220/rails-app/config/initializers/load_notification_subscribers.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-Dir[Rails.root.join('app', 'subscribers', '**', '*_subscriber.rb')].each do |subscriber_file|
-    require subscriber_file
-  end
diff --git a/lessons/220/rails-app/config/initializers/prometheus_histogram.rb b/lessons/220/rails-app/config/initializers/prometheus_histogram.rb
new file mode 100644
index 000000000..06e26aa73
--- /dev/null
+++ b/lessons/220/rails-app/config/initializers/prometheus_histogram.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+Rails.application.config.after_initialize do
+  # https://github.com/prometheus/client_ruby/pull/316
+
+  require 'prometheus/client/metric'
+
+  module Prometheus
+    module Client
+      class Histogram < Metric
+        def observe(value, labels: {})
+          bucket = buckets.bsearch { |upper_limit| upper_limit >= value  }
+          bucket = "+Inf" if bucket.nil?
+
+          base_label_set = label_set_for(labels)
+
+          # This is basically faster than doing `.merge`
+          bucket_label_set = base_label_set.dup
+          bucket_label_set[:le] = bucket.to_s
+          sum_label_set = base_label_set.dup
+          sum_label_set[:le] = "sum"
+
+          @store.synchronize do
+            @store.increment(labels: bucket_label_set, by: 1)
+            @store.increment(labels: sum_label_set, by: value)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lessons/220/rails-app/config/locales/en.yml b/lessons/220/rails-app/config/locales/en.yml
deleted file mode 100644
index 6c349ae5e..000000000
--- a/lessons/220/rails-app/config/locales/en.yml
+++ /dev/null
@@ -1,31 +0,0 @@
-# Files in the config/locales directory are used for internationalization and
-# are automatically loaded by Rails. If you want to use locales other than
-# English, add the necessary files in this directory.
-#
-# To use the locales, use `I18n.t`:
-#
-#     I18n.t "hello"
-#
-# In views, this is aliased to just `t`:
-#
-#     <%= t("hello") %>
-#
-# To use a different locale, set it with `I18n.locale`:
-#
-#     I18n.locale = :es
-#
-# This would use the information in config/locales/es.yml.
-#
-# To learn more about the API, please read the Rails Internationalization guide
-# at https://guides.rubyonrails.org/i18n.html.
-#
-# Be aware that YAML interprets the following case-insensitive strings as
-# booleans: `true`, `false`, `on`, `off`, `yes`, `no`. Therefore, these strings
-# must be quoted to be interpreted as strings. For example:
-#
-#     en:
-#       "yes": yup
-#       enabled: "ON"
-
-en:
-  hello: "Hello world"
diff --git a/lessons/220/rails-app/config/puma.rb b/lessons/220/rails-app/config/puma.rb
deleted file mode 100644
index aed85f405..000000000
--- a/lessons/220/rails-app/config/puma.rb
+++ /dev/null
@@ -1,35 +0,0 @@
-# This configuration file will be evaluated by Puma. The top-level methods that
-# are invoked here are part of Puma's configuration DSL. For more information
-# about methods provided by the DSL, see https://puma.io/puma/Puma/DSL.html.
-
-# Puma starts a configurable number of processes (workers) and each process
-# serves each request in a thread from an internal thread pool.
-#
-# The ideal number of threads per worker depends both on how much time the
-# application spends waiting for IO operations and on how much you wish to
-# to prioritize throughput over latency.
-#
-# As a rule of thumb, increasing the number of threads will increase how much
-# traffic a given process can handle (throughput), but due to CRuby's
-# Global VM Lock (GVL) it has diminishing returns and will degrade the
-# response time (latency) of the application.
-#
-# The default is set to 3 threads as it's deemed a decent compromise between
-# throughput and latency for the average Rails application.
-#
-# Any libraries that use a connection pool or another resource pool should
-# be configured to provide at least as many connections as the number of
-# threads. This includes Active Record's `pool` parameter in `database.yml`.
-workers Integer(ENV['WORKERS_NUM'] || 2)
-threads_count = ENV.fetch("RAILS_MAX_THREADS", 3)
-threads threads_count, threads_count
-
-# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
-port ENV.fetch("PORT", 8080)
-
-# Allow puma to be restarted by `bin/rails restart` command.
-plugin :tmp_restart
-
-# Specify the PID file. Defaults to tmp/pids/server.pid in development.
-# In other environments, only set the PID file if requested.
-pidfile ENV["PIDFILE"] if ENV["PIDFILE"]
diff --git a/lessons/220/rails-app/config/routes.rb b/lessons/220/rails-app/config/routes.rb
index 132c74deb..2cd7795d1 100644
--- a/lessons/220/rails-app/config/routes.rb
+++ b/lessons/220/rails-app/config/routes.rb
@@ -1,7 +1,6 @@
 Rails.application.routes.draw do
-
-  scope(:path => '/api') do
-    resources :devices
+  scope(path: "/api") do
+    resources :devices, only: %i[index create]
   end
 
   # Reveal health status on /up that returns 200 if the app boots with no exceptions, otherwise 500.
diff --git a/lessons/220/rails-app/config/storage.yml b/lessons/220/rails-app/config/storage.yml
deleted file mode 100644
index 4942ab669..000000000
--- a/lessons/220/rails-app/config/storage.yml
+++ /dev/null
@@ -1,34 +0,0 @@
-test:
-  service: Disk
-  root: <%= Rails.root.join("tmp/storage") %>
-
-local:
-  service: Disk
-  root: <%= Rails.root.join("storage") %>
-
-# Use bin/rails credentials:edit to set the AWS secrets (as aws:access_key_id|secret_access_key)
-# amazon:
-#   service: S3
-#   access_key_id: <%= Rails.application.credentials.dig(:aws, :access_key_id) %>
-#   secret_access_key: <%= Rails.application.credentials.dig(:aws, :secret_access_key) %>
-#   region: us-east-1
-#   bucket: your_own_bucket-<%= Rails.env %>
-
-# Remember not to checkin your GCS keyfile to a repository
-# google:
-#   service: GCS
-#   project: your_project
-#   credentials: <%= Rails.root.join("path/to/gcs.keyfile") %>
-#   bucket: your_own_bucket-<%= Rails.env %>
-
-# Use bin/rails credentials:edit to set the Azure Storage secret (as azure_storage:storage_access_key)
-# microsoft:
-#   service: AzureStorage
-#   storage_account_name: your_account_name
-#   storage_access_key: <%= Rails.application.credentials.dig(:azure_storage, :storage_access_key) %>
-#   container: your_container_name-<%= Rails.env %>
-
-# mirror:
-#   service: Mirror
-#   primary: local
-#   mirrors: [ amazon, google, microsoft ]
diff --git a/lessons/220/rails-app/lib/prometheus_client.rb b/lessons/220/rails-app/lib/prometheus_client.rb
new file mode 100644
index 000000000..4a2f84424
--- /dev/null
+++ b/lessons/220/rails-app/lib/prometheus_client.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+class PrometheusClient
+  DB_OP = { op: "db" }.freeze
+  BUCKETS = [
+    0.00001, 0.000015, 0.00002, 0.000025, 0.00003, 0.000035, 0.00004, 0.000045,
+    0.00005, 0.000055, 0.00006, 0.000065, 0.00007, 0.000075, 0.00008, 0.000085,
+    0.00009, 0.000095, 0.0001, 0.000101, 0.000102, 0.000103, 0.000104, 0.000105,
+    0.000106, 0.000107, 0.000108, 0.000109, 0.00011, 0.000111, 0.000112, 0.000113,
+    0.000114, 0.000115, 0.000116, 0.000117, 0.000118, 0.000119, 0.00012, 0.000121,
+    0.000122, 0.000123, 0.000124, 0.000125, 0.000126, 0.000127, 0.000128,
+    0.000129, 0.00013, 0.000131, 0.000132, 0.000133, 0.000134, 0.000135, 0.000136,
+    0.000137, 0.000138, 0.000139, 0.00014, 0.000141, 0.000142, 0.000143, 0.000144,
+    0.000145, 0.000146, 0.000147, 0.000148, 0.000149, 0.00015, 0.000151, 0.000152,
+    0.000153, 0.000154, 0.000155, 0.000156, 0.000157, 0.000158, 0.000159, 0.00016,
+    0.000161, 0.000162, 0.000163, 0.000164, 0.000165, 0.000166, 0.000167,
+    0.000168, 0.000169, 0.00017, 0.000171, 0.000172, 0.000173, 0.000174, 0.000175,
+    0.000176, 0.000177, 0.000178, 0.000179, 0.00018, 0.000181, 0.000182, 0.000183,
+    0.000184, 0.000185, 0.000186, 0.000187, 0.000188, 0.000189, 0.00019, 0.000191,
+    0.000192, 0.000193, 0.000194, 0.000195, 0.000196, 0.000197, 0.000198,
+    0.000199, 0.0002, 0.00021, 0.00022, 0.00023, 0.00024, 0.00025, 0.00026,
+    0.00027, 0.00028, 0.00029, 0.0003, 0.00031, 0.00032, 0.00033, 0.00034,
+    0.00035, 0.00036, 0.00037, 0.00038, 0.00039, 0.0004, 0.00041, 0.00042,
+    0.00043, 0.00044, 0.00045, 0.00046, 0.00047, 0.00048, 0.00049, 0.0005,
+    0.00051, 0.00052, 0.00053, 0.00054, 0.00055, 0.00056, 0.00057, 0.00058,
+    0.00059, 0.0006, 0.00061, 0.00062, 0.00063, 0.00064, 0.00065, 0.00066,
+    0.00067, 0.00068, 0.00069, 0.0007, 0.00071, 0.00072, 0.00073, 0.00074,
+    0.00075, 0.00076, 0.00077, 0.00078, 0.00079, 0.0008, 0.00081, 0.00082,
+    0.00083, 0.00084, 0.00085, 0.00086, 0.00087, 0.00088, 0.00089, 0.0009,
+    0.00091, 0.00092, 0.00093, 0.00094, 0.00095, 0.00096, 0.00097, 0.00098,
+    0.00099, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005,
+    0.0055, 0.006, 0.0065, 0.007, 0.0075, 0.008, 0.0085, 0.009, 0.0095, 0.01,
+    0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07,
+    0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45,
+    0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.5, 2.0, 2.5,
+    3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0,
+    10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5
+  ].freeze
+
+  class << self
+    def client
+      @client ||= Prometheus::Client.registry
+    end
+
+    def create_device_histogram
+      @create_device_histogram ||= client.histogram(
+        :myapp_request_duration_seconds, docstring: "Duration of the request.", labels: [ :op ], buckets: BUCKETS
+      )
+    end
+
+    def db_histogram
+      @db_histogram ||= create_device_histogram.with_labels(DB_OP)
+    end
+  end
+end
diff --git a/lessons/220/rails-app/lib/tasks/migrate_with_sql.rake b/lessons/220/rails-app/lib/tasks/migrate_with_sql.rake
deleted file mode 100644
index 2bdd44cf6..000000000
--- a/lessons/220/rails-app/lib/tasks/migrate_with_sql.rake
+++ /dev/null
@@ -1,7 +0,0 @@
-namespace :db do
-    desc 'Make migration with output'
-    task(:migrate_with_sql => :environment) do
-      ActiveRecord::Base.logger = Logger.new(STDOUT)
-      Rake::Task['db:migrate'].invoke
-    end
-  end
\ No newline at end of file
diff --git a/lessons/220/ruby-app/Gemfile b/lessons/220/ruby-app/Gemfile
index 251297ce2..eefee89d8 100644
--- a/lessons/220/ruby-app/Gemfile
+++ b/lessons/220/ruby-app/Gemfile
@@ -10,4 +10,5 @@ gem 'standalone_migrations', require: false
 gem 'oj'
 gem 'prometheus-client'
 gem 'rack'
-gem 'rage-iodine'
+gem 'rage-rb'
+gem 'falcon'
diff --git a/lessons/220/ruby-app/README.md b/lessons/220/ruby-app/README.md
index cfe57e741..b3e238ae4 100644
--- a/lessons/220/ruby-app/README.md
+++ b/lessons/220/ruby-app/README.md
@@ -16,15 +16,13 @@ bin/iodine -p 8080
 Defaults
 ```bash
 WORKERS_NUM=2
-RAILS_MAX_THREADS=2
-
 ```
 
 ### Local benchmark
 
 #### `rails-app`
 ```bash
-WORKERS_NUM=2 RAILS_MAX_THREADS=2 RAILS_ENV=production rs
+WORKERS_NUM=2 RAILS_ENV=production rs
 wrk -c 10 -t 2 -d 10 --latency http://localhost:8080/api/devices
 Running 10s test @ http://localhost:8080/api/devices
   2 threads and 10 connections
@@ -43,7 +41,7 @@ Transfer/sec:      4.56MB
 
 #### `ruby-app`
 ```bash
-WORKERS_NUM=2 RAILS_MAX_THREADS=2 bin/iodine -p 8080 config.ru
+WORKERS_NUM=2 bin/iodine -p 8080 config.ru
 wrk -c 10 -t 2 -d 10 --latency http://localhost:8080/api/devices
 Running 10s test @ http://localhost:8080/api/devices
   2 threads and 10 connections
diff --git a/lessons/220/ruby-app/config.ru b/lessons/220/ruby-app/config.ru
index 730bd7ec1..1961278b7 100644
--- a/lessons/220/ruby-app/config.ru
+++ b/lessons/220/ruby-app/config.ru
@@ -1,26 +1,31 @@
 # frozen_string_literal: true
 
 require 'connection_pool'
-require 'iodine'
 require 'oj'
 require 'pg'
 require 'prometheus/middleware/exporter'
 require 'rack'
+require 'rage'
+require 'rage/fiber'
+require 'rage/fiber_scheduler'
+require 'rage/middleware/fiber_wrapper'
 require 'yaml'
 
 require_relative 'src/app'
 
 RubyVM::YJIT.enable
-Iodine.threads = ENV.fetch('RAILS_MAX_THREADS', 2).to_i
+Iodine.threads = 1
 Iodine.workers = ENV.fetch('WORKERS_NUM', 2).to_i
+
 Oj.default_options = { mode: :compat }
 pg_conf = YAML.load(File.read('db/config.yml'), aliases: true)['production']
-PG_POOL = ConnectionPool.new(size: Iodine.threads * Iodine.workers, timeout: 5) do
+PG_POOL = ConnectionPool.new(size: pg_conf['pool'], timeout: 5) do
   PG.connect(pg_conf['host'], pg_conf['port'], nil, nil, pg_conf['database'], pg_conf['username'], pg_conf['password'])
 end
 
 # Enable if http metrics are required
 # use Prometheus::Middleware::Collector
+use Rage::FiberWrapper
 use Prometheus::Middleware::Exporter
 
 run App.new
diff --git a/lessons/220/ruby-app/db/config.yml b/lessons/220/ruby-app/db/config.yml
index 01535dbc2..d6a8c84bb 100644
--- a/lessons/220/ruby-app/db/config.yml
+++ b/lessons/220/ruby-app/db/config.yml
@@ -1,10 +1,13 @@
 ---
 default: &default
   adapter: postgresql
-  host: localhost
-  database: putratest
-  username: appodeal
-  password: pass
+  encoding: unicode
+  timeout: 5000
+  host: postgresql.antonputra.pvt
+  database: mydb
+  pool: 50
+  username: rails
+  password: devops123
 
 development:
   <<: *default
diff --git a/lessons/220/ruby-app/src/prometheus_client.rb b/lessons/220/ruby-app/src/prometheus_client.rb
index e925a6b08..05cdb26f9 100644
--- a/lessons/220/ruby-app/src/prometheus_client.rb
+++ b/lessons/220/ruby-app/src/prometheus_client.rb
@@ -2,6 +2,33 @@
 
 require 'prometheus/client'
 
+# https://github.com/prometheus/client_ruby/pull/316
+require 'prometheus/client/metric'
+
+module Prometheus
+  module Client
+    class Histogram < Metric
+      def observe(value, labels: {})
+        bucket = buckets.bsearch { |upper_limit| upper_limit >= value  }
+        bucket = "+Inf" if bucket.nil?
+
+        base_label_set = label_set_for(labels)
+
+        # This is basically faster than doing `.merge`
+        bucket_label_set = base_label_set.dup
+        bucket_label_set[:le] = bucket.to_s
+        sum_label_set = base_label_set.dup
+        sum_label_set[:le] = "sum"
+
+        @store.synchronize do
+          @store.increment(labels: bucket_label_set, by: 1)
+          @store.increment(labels: sum_label_set, by: value)
+        end
+      end
+    end
+  end
+end
+
 class PrometheusClient
   BUCKETS = [
     0.00001, 0.000015, 0.00002, 0.000025, 0.00003, 0.000035, 0.00004, 0.000045,