Librarian is a bundler for Ruby. It handles dependency checking for you. The project for using Librarian with Puppet is called librarian-puppet and is available at http://rubygems.org/gems/librarian-puppet. To install librarian-puppet, we'll use RubyGems since no rpm packages exist in public repositories at this time. To make our instructions platform agnostic, we'll use Puppet to install the package as shown here:

[root@stand ~]# puppet resource package librarian-puppet ensure=installed provider=gem
Notice: /Package[librarian-puppet]/ensure: created
package { 'librarian-puppet':
ensure => ['2.2.1'],
}

We can now run librarian-puppet as follows:

[root@stand ~]# librarian-puppet version
librarian-puppet v2.2.1

The librarian-puppet project uses a Puppetfile to define the modules that will be installed. The syntax is the name of the module followed by a comma and the version to install. Modules may be pulled in from Git repositories or directly from Puppet Forge. You can override the location of Puppet Forge using a forge line as well. Our initial Puppetfile would be the following:

forge "http://forge.puppetlabs.com"
mod 'puppetlabs/puppetdb', '5.0.0'
mod 'puppetlabs/stdlib', '4.9.0'

We'll create a new public directory in /tmp/public4 and include the Puppetfile in that directory, as shown here:

[git@stand ~]$ cd /tmp
[git@stand tmp]$ mkdir public4 && cd public4
[git@stand public4]$ cat<<EOF>Puppetfile
> forge "https://forgeapi.puppetlabs.com"
>mod 'puppetlabs/puppetdb', '5.0.0'
>mod 'puppetlabs/stdlib', '4.9.0'
> EOF

Next, we'll tell librarian-puppet to install everything we've listed in the Puppetfile as follows:

[git@stand public4]$ librarian-puppet update
[git@stand public4]$ ls
modules  Puppetfile  Puppetfile.lock

The Puppetfile.lock file is a file used by librarian-puppet to keep track of installed versions and dependencies; in our example, it contains the following:

FORGE
remote: https://forgeapi.puppetlabs.com
specs:
puppetlabs-apt (2.2.0)
puppetlabs-stdlib (< 5.0.0, >= 4.5.0)
puppetlabs-concat (1.2.4)
puppetlabs-stdlib (< 5.0.0, >= 3.2.0)
puppetlabs-firewall (1.7.1)
puppetlabs-inifile (1.4.2)
puppetlabs-postgresql (4.6.0)
puppetlabs-apt (< 3.0.0, >= 1.8.0)
puppetlabs-concat (< 2.0.0, >= 1.1.0)
puppetlabs-stdlib (~> 4.0)
puppetlabs-puppetdb (5.0.0)
puppetlabs-firewall (< 2.0.0, >= 1.1.3)
puppetlabs-inifile (< 2.0.0, >= 1.1.3)
puppetlabs-postgresql (< 5.0.0, >= 4.0.0)
puppetlabs-stdlib (< 5.0.0, >= 4.2.2)
puppetlabs-stdlib (4.9.0)

DEPENDENCIES
puppetlabs-puppetdb (= 5.0.0)
puppetlabs-stdlib (= 4.9.0)

Our modules are installed in /tmp/public4/modules. Now, we can go back and add all these modules to our initial Puppetfile to lockdown the versions of the modules for all our developers. The process for a developer to clone our working tree would be to install librarian-puppet and then pull down our Puppetfile. We will add the Puppetfile to our Git repository to complete the workflow. Thus, each developer will be guaranteed to have the same public module structure.

We can then move these modules to /etc/puppetlabs/code/modules and change permissions for the Puppet user using the following commands:

[root@stand ~]# cd /tmp/public4/modules/
[root@stand modules]# cp -a . /etc/puppetlabs/code/modules/
[root@stand modules]# chown -R puppet:puppet /etc/puppetlabs/code/modules
[root@stand modules]# ls /etc/puppetlabs/code/modules/
apt  concat  firewall  inifile  postgresql  puppetdb  stdlib

This method works fairly well, but we still need to update the modules independently of our Git updates; we need to do these two actions together. This is where r10k comes into play.