Using a rackup file to custom configure an application instance - ruby

Question

tl;dr How can I get a single Sinatra app to start up very differently on different servers via customizations to config.ru?
Background
I have a single web application written using Sinatra that's run on different servers. Currently the codebase for these servers is forked because there are some non-trivial differences in the way (discrete) parts of them work. For example:
one server authenticates users via an intranet LDAP server, while another server uses a simpler local database table lookup.
one server uses an external cron job to periodically update some statistics, while another (Windows-based) server uses an internal sleepy Thread.
one server stores certain metadata in a local table, while another server pulls the metadata from an external Wiki via screen scraping (!).
…and so on.
I'd like to get these code bases completely shared (single Git repo). I envision that each server would have one slightly-differing configuration file that causes the app to be started up differently.
Abandoned Solutions
I could change the behavior of the app based on environment variables. As there are a not-tiny number of variations in behavior, I'd rather not hide the settings in environment variables.
I could create my own "server-settings.rb" file that is unique to each machine, require it in my app.rb, and then change the configuration there. However, this seems to possibly be re-inventing the wheel. I already have a file named config.ru for each server. Shouldn't I be using this?
The Current Code
My config.ru for the app currently is simply:
require ::File.join( ::File.dirname(__FILE__), 'app' )
run MyApp.new
And the app.rb that it requires is, in essence:
require 'sinatra'
require_relative 'helpers/login' # customized for LDAP lookup on this server
class MyApp < Sinatra::Application
use Rack::Session::Cookie, key:'foo.bar', path:'/', secret:'ohnoes'
set :protection, except: [:path_traversal, :session_hijacking]
configure :production do
# run various code that depends on server settings, e.g.
Snapshotter.start # there is no cron on this machine, so we do it ourselves
end
configure :development do
# run various code that depends on server settings
end
end
The Question
I'd like to make config.ru live up to its name, and have it look something like this:
require ::File.join( ::File.dirname(__FILE__), 'app' )
run MyApp.new( auth: :ldap, snapshot:false, metadata: :remote_wiki, … )
How can I modify my application to change its configuration behavior based on settings supplied via config.ru? Or is this an abuse of config.ru, trying to use it for totally the wrong thing?

Answer 1

As soon as I started reading the question the first answer to pop into my head was "environment variable" but you scotched that straight away :)
I'll go with a mixture of one of your coulds and the desired outcome code, as it's how I structure things…
Because I want to be able to test my applications more easily, I take most of the Ruby out of the config.ru and into a separate config.rb file and leave config.ru to be a bootstrap file. So my standard skel is:
config.ru
# encoding: UTF-8
require 'rubygems'
require 'bundler'
Bundler.setup
root = File.expand_path File.dirname(__FILE__)
require File.join( root , "./app/config.rb" )
# everything was moved into a separate module/file to make it easier to set up tests
map "/" do
run APP_NAME.app
end
app/config.rb
# encoding: utf-8
require_relative File.expand_path(File.join File.dirname(__FILE__), "../lib/ext/warn.rb")
require_relative "./init.rb" # config
require_relative "./main.rb" # routes and helpers
require 'encrypted_cookie'
# standard cookie settings
COOKIE_SETTINGS = {
:key => 'usr',
:path => "/",
:expire_after => 86400, # In seconds, 1 day
:secret => ENV["LLAVE"],
:httponly => true
}
module APP_NAME # overall name of the app
require 'rack/ssl' # force SSL
require 'rack/csrf'
if ENV["RACK_ENV"] == "development"
require 'pry'
require 'pry-nav'
end
# from http://devcenter.heroku.com/articles/ruby#logging
$stdout.sync = true
ONE_MONTH = 60 * 60 * 24 * 30
def self.app
Rack::Builder.app do
cookie_settings = COOKIE_SETTINGS
# more security if in production
cookie_settings.merge!( :secure => true ) if ENV["RACK_ENV"] == "production"
# AES encryption of cookies
use Rack::Session::EncryptedCookie, cookie_settings
if ENV["RACK_ENV"] == "production"
use Rack::SSL, :hsts => {:expires => ONE_MONTH}
end
# to stop XSS
use Rack::Csrf, :raise => true unless ENV["RACK_ENV"] == "test"
run App # the main Sinatra app
end
end # self.app
end # APP_NAME
The initial reason I did this was making it easy to run the app in specs:
shared_context "All routes" do
include Rack::Test::Methods
let(:app){ APP_NAME.app }
end
but it makes sense to me to keep this code with the rest of the application code, so to speak, as I can bundle things together, run other apps etc. I've used this to conditionally load different examples into the specs in a few projects (it helps cut down on duplicated effort and check the examples really work), so I don't see why you couldn't use it to conditionally load configurations.
This way you get to choose to use a conditional in the config.ru as to which config.rb file you would use, or use an env var in the config.rb as to which definiton of self.app to use , or pass in an options hash to self.app…
With your set up I'd rename the APP_NAME module to MyApp, and the Sinatra class to App (because quite often I'll have an website that runs a front end and an API, so the Sinatra classes get named by their function (App, API etc) and wrapped in a module named after the site) and end up with:
config.ru
map "/" do
run MyApp.app( auth: :ldap, snapshot:false, metadata: :remote_wiki )
end
config.rb
def self.app( opts={} )
opts = DEFAULT_OPTIONS.merge opts
# …
run App
end
It'll be interesting to see how other people tackle this.