danott/application.rb Secret

## application.rb
# Hey Bike Shed!
#
# During the episode titled "Sportsaphores", Chris shared about setting up
# primary/replica/leader/follower/whatchamacallit databases. Something mentioned during that
# conversation was the discouragement that comes from losing production/development parity,
# especially for catching bugs before production. The big hurdle mentioned, was wanting to avoid
# the overhead of setting up a proper "follower" database.
#
# I wanted to share something I've done in development/test that has caught similar bugs in my
# Rails 6 app with multiple database connections. The "one weird trick", is to establish
# configuration for a leader and a follower... they just happen to point to the same database.
# If you include the `"replica" => true` attribute in your configuration Hash, ActiveRecord will
# give similiar-enough characteristics as a true read-only replica.
#
# Here's a little demo app that shows the runtime error that will happen when trying to write
# when the "replica" attribute is set.
#
# Run this with `ruby application.rb`
require "bundler/inline"

gemfile true do
  source "https://rubygems.org"
  gem "rails", "~> 6.1"
  gem "sqlite3"
end

require "action_controller/railtie"
require "active_record/railtie"
require "rails/command"
require "rails/commands/server/server_command"

ActiveRecord::Base.configurations = ActiveRecord::DatabaseConfigurations.new({
  "development" => {
    "primary" => {
      "adapter" => "sqlite3",
      "database" => "tmp/application.sqlite",
      "replica" => false,
    },
    "replica" => {
      "adapter" => "sqlite3",
      "database" => "tmp/application.sqlite",

      # This is the secret sauce. Connect to the same database, but mark it as a replica.
      # This will give development/test the same ActiveRecord runtime characteristics as
      # production without the overhead of spinning up an actual follower database.
      "replica" => true,
    },
  }
})
ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection

ActiveRecord::Schema.define do
  create_table :logged_get_requests, force: true do |t|
    t.timestamps
  end
end

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  connects_to database: { writing: :primary, reading: :replica }
end

class LoggedGetRequest < ApplicationRecord; end

class ApplicationController < ActionController::Base; end

class DemosController < ApplicationController
  delegate :demo_path, to: "Rails.application.routes.url_helpers"
  delegate :link_to, to: "helpers"

  def show
    database_role_from_param = params.fetch(:role, "reading")
    attempt_create = params.fetch(:attempt_create, "nope") == "yep"

    count = "not set"
    error = "no error encountered"

    ActiveRecord::Base.connected_to(role: database_role_from_param) do
      begin
        LoggedGetRequest.create! if attempt_create
        count = LoggedGetRequest.all.count
      rescue => e
        error = "#{e.class}: #{e.message}"
      end
    end

    render inline: <<~HTML
      <html>
        <body>
          <h1>Current count: #{count}</h1>
          <h2>Current error: #{error}</h2>
          <ul>
            <li>#{link_to "Get without create on primary", demo_path(role: :writing, attempt_create: "nope")}</li>
            <li>#{link_to "Get without create on replica", demo_path(role: :reading, attempt_create: "nope")}</li>
            <li>#{link_to "Get with create on primary", demo_path(role: :writing, attempt_create: "yep")}</li>
            <li>#{link_to "Get with create on replica", demo_path(role: :reading, attempt_create: "yep")}</li>
          </ul>
        </body>
      </html>
    HTML
  end

end

class Application < Rails::Application
  config.secret_key_base = ENV["SECRET_KEY_BASE"] || SecureRandom.hex
  config.secret_token = ENV["SECRET_TOKEN"] || SecureRandom.hex

  config.logger = Logger.new($stdout)
  Rails.logger = config.logger

  routes.draw do
    resource :demo, only: %i[show update]
    root "demos#show"
  end
end

Rails::Server.new(app: Application, Host: "0.0.0.0", Port: 3000).start
	# Hey Bike Shed!
	#
	# During the episode titled "Sportsaphores", Chris shared about setting up
	# primary/replica/leader/follower/whatchamacallit databases. Something mentioned during that
	# conversation was the discouragement that comes from losing production/development parity,
	# especially for catching bugs before production. The big hurdle mentioned, was wanting to avoid
	# the overhead of setting up a proper "follower" database.
	#
	# I wanted to share something I've done in development/test that has caught similar bugs in my
	# Rails 6 app with multiple database connections. The "one weird trick", is to establish
	# configuration for a leader and a follower... they just happen to point to the same database.
	# If you include the `"replica" => true` attribute in your configuration Hash, ActiveRecord will
	# give similiar-enough characteristics as a true read-only replica.
	#
	# Here's a little demo app that shows the runtime error that will happen when trying to write
	# when the "replica" attribute is set.
	#
	# Run this with `ruby application.rb`
	require "bundler/inline"

	gemfile true do
	source "https://rubygems.org"
	gem "rails", "~> 6.1"
	gem "sqlite3"
	end

	require "action_controller/railtie"
	require "active_record/railtie"
	require "rails/command"
	require "rails/commands/server/server_command"

	ActiveRecord::Base.configurations = ActiveRecord::DatabaseConfigurations.new({
	"development" => {
	"primary" => {
	"adapter" => "sqlite3",
	"database" => "tmp/application.sqlite",
	"replica" => false,
	},
	"replica" => {
	"adapter" => "sqlite3",
	"database" => "tmp/application.sqlite",

	# This is the secret sauce. Connect to the same database, but mark it as a replica.
	# This will give development/test the same ActiveRecord runtime characteristics as
	# production without the overhead of spinning up an actual follower database.
	"replica" => true,
	},
	}
	})
	ActiveRecord::Base.logger = Logger.new(STDOUT)
	ActiveRecord::Base.establish_connection

	ActiveRecord::Schema.define do
	create_table :logged_get_requests, force: true do \|t\|
	t.timestamps
	end
	end

	class ApplicationRecord < ActiveRecord::Base
	self.abstract_class = true
	connects_to database: { writing: :primary, reading: :replica }
	end

	class LoggedGetRequest < ApplicationRecord; end

	class ApplicationController < ActionController::Base; end

	class DemosController < ApplicationController
	delegate :demo_path, to: "Rails.application.routes.url_helpers"
	delegate :link_to, to: "helpers"

	def show
	database_role_from_param = params.fetch(:role, "reading")
	attempt_create = params.fetch(:attempt_create, "nope") == "yep"

	count = "not set"
	error = "no error encountered"

	ActiveRecord::Base.connected_to(role: database_role_from_param) do
	begin
	LoggedGetRequest.create! if attempt_create
	count = LoggedGetRequest.all.count
	rescue => e
	error = "#{e.class}: #{e.message}"
	end
	end

	render inline: <<~HTML
	<html>
	<body>
	<h1>Current count: #{count}</h1>
	<h2>Current error: #{error}</h2>
	<ul>
	<li>#{link_to "Get without create on primary", demo_path(role: :writing, attempt_create: "nope")}</li>
	<li>#{link_to "Get without create on replica", demo_path(role: :reading, attempt_create: "nope")}</li>
	<li>#{link_to "Get with create on primary", demo_path(role: :writing, attempt_create: "yep")}</li>
	<li>#{link_to "Get with create on replica", demo_path(role: :reading, attempt_create: "yep")}</li>
	</ul>
	</body>
	</html>
	HTML
	end

	end

	class Application < Rails::Application
	config.secret_key_base = ENV["SECRET_KEY_BASE"] \|\| SecureRandom.hex
	config.secret_token = ENV["SECRET_TOKEN"] \|\| SecureRandom.hex

	config.logger = Logger.new($stdout)
	Rails.logger = config.logger

	routes.draw do
	resource :demo, only: %i[show update]
	root "demos#show"
	end
	end

	Rails::Server.new(app: Application, Host: "0.0.0.0", Port: 3000).start