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KingSoa

KingSoa orchestrates a SOA landscape, by knowing where services live and how to call them. It exposes service calls as ruby methods (KingSoa.my_method) which are transfered into http rpc or local method calls. KingSoa lives on the sender and receiver side.

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

Gem Dependencies

  • 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(on send)

  • activesupport

Usage

Take your time and READ the code, its only three files with combined 180 lines of code and lots of documentation. The tests with a high coverage serve as another great source of information.

Simply put: RTFC(Read The Fucking Code) and RTFT

The Service Registry

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

A service(KingSoa::Service) has a name and two settings(queue or url) defining how it is being called. The actual service class can be located local, remote(http) or somewhere in a worker when beeing queued. The service call is received by a self.perform method of a class named like the CamelCased service.name. It is up to you define service arguments or define and use return values.

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(NO url) 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. All arguments MUST be json encodable!!
KingSoa.crunch_image(image_path)
KingSoa.increment_usage(12)  
KingSoa.delete_user(user_id)

A simple service class, located in the app above

class IncrementUsage
  self.perform(value)
    current_user.update_attribute(:usage, value)
  end
end

Remote Services

All transport is done over http. An http call can 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 somewhere on your farm.

Service endpoints receiving authenticated calls should use the provided rack middleware. As it is doing the authentication, executing the service class and returns values or errors.

KingSoa::Service.new( :name => :increment_usage,
                      :url  => 'http://localhost:4567',
                      :auth => '12345')

Service options

  • :name => KingSoa.increment_usage calls IncrementUsage.perform

  • :url => url to which the request goes out in form of +[method] URL:Port+ examples: ( http omitted to prevent auto linking)

    '://my_uri'

    POST request, default without http verb

    'GET ://my_uri:6969'

    GET to port 6969

    'DELETE ://my_uri'

    DELETE something

    'PUT ://my_uri:6669'

    PUT it down

  • :auth => optional authentication string OR integer, should also be known (defined) on the receiving side.

The remote side is always called the following url parameters. And its up to you to handle those, if you are NOT using the rack middleware.

http://my_uri?name=increment_usage
             &auth=1234
             &args={12}    #json encoded args as string

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. It is up to you to check or validate the existence of arguments and work with return values.

KingSoa::Service.new(:name => :crunch_image)
# call service
KingSoa.crunch_image('/path')
# translates into
CrunchImage.perform('/path')

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 rescheduled if it fails. Queued methods can not have return values => fire & forget

KingSoa::Service.new(:name => :delete_user,
                     :queue => :deletions)

:queue => name of the queue as defined by resque. Actually used as prefix in redis

Example of a receiving resque worker class:

class DeleteUser
  @queue = :deletions
  self.perform(user_id)
    User.destroy(user_id)
  end
end

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

Rack Middleware

The included middleware provides some convinience on the receiving side. It does the authentication and relies on json for incoming requests and outgoing responses. For incomming request the url param[args] is automaticly json decoded.

Response on success

HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 1234
'{result:{whatever you return .. if you care}}'

Response on error

HTTP/1.0 500 Server Error
Content-Type: application/json
Content-Length: 1234
'{error:'error msg as string'}'

The middleware, by default, grabs all incoming request to my_url/soa. This behaviour can be customized when setting it up:

config.middleware.use KingSoa::Rack::Middleware, :endpoint_path =>'/incoming_soa'

grabs all requests to: my_url/incoming_soa

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 with clients getting service 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

Copyright © 2010 Georg Leciejewski. See LICENSE for details.

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