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Create a hub for your server configuration. Use it with Capistrano, Puppet and others.

Meet Hubcap

You want to provision your servers with Puppet. You want to deploy to your servers with Capistrano. Where do you define your server infrastructure?

Hubcap lets you define the characteristics of your servers once. Then, when you need to use Puppet, Capistrano drives. It deploys your Puppet modules and manifests, plus a special host-specific file, and applies it to the server. (This is sometimes called "masterless Puppet". It has a lot of benefits that derive from decentralization and pushing changes on-demand.)

Here's a really simple infrastructure configuration file:

group('us') {
  server('') {
    cap_attribute(:primary => true)
  server('') {
    cap_attribute(:no_release => true)

group('au') {
  server('') {
    role(:app, :db)
    cap_attribute(:primary => true)

Using this config, you could tell Capistrano to deploy to all servers, servers in one group, or just a single server.

Here's a more advanced example - an application that can be deployed to a set of staging servers or a larger set of production servers. It has special parameters that Puppet will use.

# An application called 'readme' that uses Cap's default deployment recipe.
application('readme', :recipes => 'deploy') {
  # Set a capistrano variable.
  cap_set('repository', '')

  # Declare that all servers will have the 'baseline' puppet class.

  group('staging') {
    # Puppet will have a $::exception_subject_prefix variable on these servers.
    param('exception_subject_prefix' => '[STAGING] ')
    # For simple staging, just one server that does everything.
    server('readme.stage', :address => '') {
      cap_role(:web, :app, :db)
      puppet_role('proxy', 'app', 'db')

  group('production') {
    # Puppet will have these top-scope variables on all these servers.
      'exception_subject_prefix' => '[PRODUCTION] ',
      'env' => {
        'FORCE_SSL' => true,
        'S3_KEY' => 'AKIAKJRK23943202JK',
        'S3_SECRET' => 'KDJkaddsalkjfkawjri32jkjaklvjgakljkj'

    group('proxy') {
      # Servers will have the :web role and the 'proxy' puppet class.
      server('proxy-1', :address => '')

    group('app') {
      # Servers will have the :app role and the 'app' puppet class.
      server('app-1', :address => '')
      server('app-2', :address => '')

    group('db') {
      server('db-1', :address => '')

Save this as example.rb in a hub subdirectory of the location of your Capfile.


$ hubcap ALL servers:tree

That's a lot of info. You can filter your server list to target specific groups of servers:

$ `hubcap example.vagrant servers:tree`

You can run list in place of tree to see just the servers that match your filter:

$ `hubcap example.production.db servers:tree`

Working with Puppet

You should have your Puppet modules in a git repository. The location of this repository should be specified in your Capfile with set(:puppet_repository, '...'). Your site manifest should be within this repo at puppet/host.pp (but this is also configurable).

When you're ready to provision some servers:

$ `hubcap example.vagrant puppet:noop`
$ `hubcap example.vagrant puppet:apply`

Once that's done, you can deploy your app in the usual way:

$ `hubcap example.vagrant deploy:setup deploy:cold`

The Hubcap DSL

The Hubcap DSL is very simple. This is the basic set of statements:

  • group - A named set of servers, roles, variables, attributes. Groups can be nested.

  • application - A special kind of group. You can pass :recipes => ... to this declaration. Each recipe path will be loaded into Capistrano only for this application. Applications can't be nested.

  • server - An actual host that you are managing with Capistrano and Puppet. The first argument is the name, which can be an IP address or domain name if you like. Otherwise, pass :address => '...'.

  • cap_set - Set a Capistrano variable.

  • cap_attribute - Set a Cap attribute on all the servers within this group, such as :primary => true or :no_release => true.

  • role - Add a role to the list of Capistrano roles for servers within this group. By default, these roles are supplied as classes to apply to the host in Puppet. You can specify that a role is Capistrano-only with cap_role(), or Puppet-only with puppet_role(). This is additive: if you have multiple role declarations in your tree, all of them apply.

  • param - Add to a hash of 'parameters' that will be supplied to Puppet as top-scope variables for servers in this group. Like role, this is additive.

Hubcap uses Puppet's External Node Classifier (ENC) feature to provide the list of classes and parameters for a specific host. More info here:

Hubcap as a library

If you'd rather run cap than hubcap, you can load your hub configuration directly in your Capfile. Add this to the end of the file:

Hubcap.load('', 'hub').configure_capistrano(self)

The two arguments to Hubcap.load are the filter (where '' means no filter), and the path to the hub configuration. This will load *.rb in the hub directory (but not subdirectories). You can specify multiple paths as additional arguments -- whole directories or specific files.

If you want to simulate the behaviour of the hubcap script, you could do it with something like this in your Capfile.

# Load servers and sets from node config. Any recipes loaded after this
# point will be available only in application mode.
if (target = ENV['TO']) && !ENV['TO'].empty?
  target = ''  if target == 'ALL'
  Hubcap.load(target, 'hub').configure_capistrano(self)
  warn('NB: No servers specified. Target a Hubcap group with TO.')

In this set-up, you'd run cap like this:

$ cap TO=example.vagrant servers:tree