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From "Arvind Creatrix IT Soft" <>
Subject Re: deltacloud as a lib and broker
Date Wed, 10 Apr 2013 20:32:53 GMT
Hi David/Martin/all,


I went through the link you provided- and I am thankful that you pointed 
that out(that the way I suggested for version negotiation)-- its simply 
outdated :( Sorry for that...

With ref to auth, if we are working on a library then should it not have 
some authentication of its own? I dont know, just a thought... This way, 
(with auth) an end user can straight away use the library as it is(one 
potential user is myself as I could straightaway deploy the library and use 
the in-built auth to make use of the deployed library from my end-user apps)

Also, as Martin has said, RABL can be used with Sinatra too- so we need not 
add Rails to the project....


I dont have experience using RABL myself-- its just that one of my friends 
has used it and recommends it.

With ref to parsing of JSON/XML objects the only Ruby libraries I am aware 
of are Representable(  and 

 -- Crack looks very suitable for this use case- although again I have never 
used it myself-- plus its very new -- so it may well have some bugs in it:(

With ref to my projects-- well a couple of them are for deploying a custom 
CMS to cloud, a cloud platform (what you would call a cloud PaaS) and a 
distributed computing platform.  In all of these, I would require DeltaCloud 
to provision/restart/perform other ops on virtual machines in different 
clouds. I initially zeroed in on jclouds but feel Delta Cloud is a better 
fit, simply because of the much larger community that is working on it, and 
also I can deploy Delta Cloud as a standalone app(accessible via API from 
each of my end user apps separately)-- which is not possible with jclouds 
(would require a lot of work).

Yours sincerely,

-----Original Message----- 
From: Martin Povolny
Sent: Wednesday, April 10, 2013 11:42 PM
Subject: Re: deltacloud as a lib and broker

On Tue, Apr 09, 2013 at 09:11:46PM +0530, Arvind Creatrix IT Soft wrote:
> Hi

Hallo Arvind.

> With ref to the discussion- I was already planning to work on creating an 
> API over the core Delta Cloud code as I need it in a number of my 
> projects.
> I suggest the following means to do this, in as painless a manner as 
> possible--
> (1) Use Rails and RABL--> to generate the 
> (2) Use the VersionCake gem for versioning( 
> (3) Controllers are set up in an hierarchy where you have one 
> BaseController which contains this authentication logic (as a 
> before_filter) and then the other controllers inherit from that. If you 
> have any other helpers, they would go in this controller too.
> (4) For authorization, use CanCan.(  It's 
> README and Wiki are great sources of information on how to use it.

I am experimenting with a cloud broker concept and actually I am trying
out Rabl on top of Sinatra w/o Padrino as this gives me most of what I
need and stays sort-of lightweight especially when comparing with Rails.

So you can provide a recommendation for Rabl? Do you have personal good
experience with it?

Then what do you use for parsing of POST data? Is there some counterpart
of Rabl that would parse XML and JSON based on similar rules and give me
a nice Ruby hash and a decent list of errors in case of any?

I also wonder what type of project you have that use DeltaCloud. Can you
share such information? What parts of DeltaCloud do you use most?

> Finally, here is some helpful text from the RABL docs-->
> Once you have installed RABL (explained above), you can construct a RABL 
> view template and then render the template from your Sinatra, Padrino or 
> Rails applications from the controller (or route) very easily. Using 
> Padrino as an example, assuming you have aPost model filled with blog 
> posts, you can render an API representation (both JSON and XML) by 
> creating a route:
> # app/app.rb
> get "/posts", :provides => [:json, :xml] do
>   @user = current_user
>   @posts = Post.order("id DESC")
>   render "posts/index"
> end
> Then we can create the following RABL template to express the API output 
> of @posts:
> # app/views/posts/index.rabl
> collection @posts
> attributes :id, :title, :subject
> child(:user) { attributes :full_name }
> node(:read) { |post| post.read_by?(@user) }
> Which would output the following JSON or XML when visiting 
> http://localhost:3000/posts.json
> [{  "post" :
>   {
>     "id" : 5, title: "...", subject: "...",
>     "user" : { full_name : "..." },
>     "read" : true
>   }
> }]
> This is an easy way to create a API library that has its own versioning- 
> and at the same time it basically just uses the core code in the Delta 
> Cloud library itself.

Martin Povolny <>
tel. +420777714458 

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