A common use-case for applications is to have Chef configure your systems and use Capistrano to deploy the applications that run on them.
Capistrano Chef is a Capistrano extension that makes Chef and Capistrano get along like best buds.
The Capistrano configuration has a facility to specify the roles for your application and which servers are members of those roles. Chef has its own roles. If you're using both Chef and Capistrano, you don't want to have to tell them both about which servers you'll be deploying to, especially if they change often.
capistrano-chef provides some helpers to query your Chef server from Capistrano to define these roles.
A normal deploy.rb in an app using capistrano defines a roles like this:
role :web, '10.0.0.2', '10.0.0.3'
role :db, '10.0.0.2', :primary => true
Using capistrano-chef, you can do this:
require 'capistrano/chef'
chef_role :web 'roles:web'
chef_role :db, 'roles:database_master', :primary => true,
:attribute => :private_ip
This defines the same roles using Chef's search feature. Nodes are searched using the given query. The node's ipaddress attribute is used by default, but another (top-level) attribute can be specified in the options. The rest of the options are the same as those used by Capistrano.
Chef Data Bags let you store arbitrary JSON data. A common pattern is to use an apps data bag to store data about an application for use in configuration and deployment.
Chef also has a Deploy Resource described in on of their blog posts, Data Driven Application Deployment with Chef. This is one method of deploying, but, if you're reading this, you're probably interested in deploying with Capistrano.
If you create an apps data bag item (let's call it myapp), Capistrano Chef will let you use the data in your Capistrano recipes with the set_from_data_bag method.
This will allow you to store all of your metadata about your app in one place.
In normal Capistrano deploy.rb:
set :application, 'myapp'
set :user, 'myapp'
set :deploy_to, '/var/apps/myapp'
set :scm, :git
... # and so on
With Capistrano Chef, an apps data bag item:
{
"id": "myapp",
"user": "myapp",
"deploy_to": "/var/apps/myapp",
"scm": "git",
... // and so on
}
And in thedeploy.rb:
set :application, 'myapp'
set_from_data_bag
A Chef server is expected to be available and Knife is used to configure the extension, looking for knife.rb the keys needed in .chef in the current directory or one its parent directories.
If you're using Opscode Hosted Chef these files will be provided for you. If not, the configuration can be generated with knife configure -i. See the Chef Documentation for more details.
Tested with Ruby Enterprise Edition 1.8.7, Ruby 1.9.2 and 1.9.3. Should work with Capistrano 2 or greater.
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