KingSoa

KingSoa orchestrates a SOA landscape, by knowing where services live and how to call them.

Why?

While your app is growing you stuff more and more in it, unrelated to its core business intelligence. You'll end up with an monolythic clumsy piece, getting harder to handle every day. Just think of: scalability, testing, deployment, ..

To keep it clean a division of responsibilities, and with it a separation into smaller parts, is needed. But now you've got a communication problem, because each part needs to know about the others. This is where KingSoa enters the stage.

Install

gem install king_soa

Dependencies

Needed gems:

  • resque => When a service has a queue set, its enqueued via resque

  • typhoeus => making http requests to remotely located services

  • json => all arguments of a service call are json encoded

Define services

The service registry(KingSoa::Registry) is keeping track of available services and behaves more or less like an array. Be aware that KingSoa::Registry is a singleton, so that the rack middleware and your app are seeing the same.

A service (KingSoa::Service) has a name and knows how its gonna be called. A service call goes out to a class named like the CamelCased service.name with an self.perform method. Depending on the service settings it can be located local, remote(http) or beeing put onto a queue.

You can define services anywhere in your app and add them to the service registry. This should most likely be done in an initalizer(Rails).

# A remote service MUST have an url and an auth key set
a = KingSoa::Service.new(:name => :increment_usage,
                      :url  => 'http://localhost:4567',
                      :auth => '12345')

# A local service calling CrunchImage.perform
b = KingSoa::Service.new(:name => :crunch_image)

# A queued service MUST have a queue name, and of course you should have a worker looking for it
c = KingSoa::Service.new(:name => :delete_user,
                         :queue => :deletions)
# register all of them
KingSoa::Registry << a << b << c

# somewhere in your app just call the services
KingSoa.increment_usage(12)
KingSoa.crunch_image(image_path)
KingSoa.delete_user(user_id)

Remote Services

The transport is done via http calls. All http calls have an authentication key to provide some minimal access restriction. To make it secure you should either use https in public or hide the endpoints somwhere on your farm.

Service endpoints receiving such calls need to use the provided rack middleware. As the middleware is doing the authentication, executing the service class and returns values or errors.

Local Services

A local service calls a class with the CamelCased service name. This class MUST have a self.perform method which receives all of the given arguments.

Queued Services

The service is put onto a resque queue and somewhere in your cloud you should have a worker looking for it. The service class should also have the resque @queue attribute set so the job can be resceduled if it fails.

Gotchas

  • make sure to define the service on the sender side with the appropriate url

  • define the local service(called from remote) with the right auth key

  • double check your auth keys(a string is not an int), to be save use “strings” esp. when loading from yml

Integration

Just think of a buch of small sinatra or specialized rails apps, each having some internal services and consuming services from others.

Rails

Add the middleware(application.rb/environment.rb) if you want to receive calls.

require 'king_soa'
config.middleware.use KingSoa::Rack::Middleware

Setup services for example in an initializer reading a services.yml file. For now there is no convinience loading method and no proposed yml format.

#services.yml
sign_document:
  queue: signings
send_sms:
  url: 'http://messaging.localhost:3000'
  auth: '12345678'

# king_soa_init 
service_defs = YAML.load_file(File.join(RAILS_ROOT, 'config', 'services.yml'))
service_defs.each do |k, v|      
  opts = { :name => k }     
  [:url, :auth, :queue].each do |opt|
    opts[opt] = v[opt.to_s] if v[opt.to_s]
  end
  KingSoa::Registry << KingSoa::Service.new(opts)
end

Sinatra

Take a look at spec/server/app where you can see a minimal sinatra implementation The base is just:

require 'king_soa'
use KingSoa::Rack::Middleware

The service definition should of course also be done, see rails example.

ToDo

  • better error logging

  • a central server & clients getting definitions from it

Note on Patches/Pull Requests

  • Fork the project.

  • Make your feature addition or bug fix.

  • Add tests for it. This is important so I don't break it in a future version unintentionally.

  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a branch or commit by itself so I can ignore when I pull)

  • Send me a pull request. Bonus points for topic branches.

Copyright © 2010 Georg Leciejewski. See LICENSE for details.