This is a sample of how sprint.ly generates a new Vagrant virtual machine to help developers get up to speed quickly.

fabfile.py

from fabric.api import *
import os

def dev_server():
    print """
This setup assumes:
* Your SPRINTLY_HOME environment variable is set to the location of the sprint.ly git checkout.
* The Sprint.ly chef setup is checked out to "$SPRINTLY_HOME/../chef"
"""
    # is Vagrant installed?
    with settings(
        hide('warnings', 'running', 'stdout', 'stderr'),
        warn_only=True
    ):
        has_vagrant = local("which vagrant", capture=True)
        if not has_vagrant:
            print "You must install vagrant from http://http://vagrantup.com in order to set up a development server VM."
            return

    # is SPRINTLY_HOME setup?
    SPRINTLY_HOME = os.environ['SPRINTLY_HOME']
    if not SPRINTLY_HOME:
        print "You must set the SPRINTLY_HOME environment variable to tell us where your local clone of the sprintly codebase is."
        return

    VAGRANT_HOME = "/".join(SPRINTLY_HOME.split("/")[0:-1])
    print "Using %s as VAGRANT_HOME: " % VAGRANT_HOME
    with settings(
        hide('warnings', 'running', 'stdout', 'stderr'),
        warn_only=True
    ):
        has_sprintly_box = local("vagrant box list | grep sprintly", capture=True)
        if not has_sprintly_box:
            print "Creating sprintly box based on lucid32. This will take a while."
            local ("vagrant box add sprintly http://files.vagrantup.com/lucid32.box", capture=True)

    # is vagrant initialized?
    dot_vagrant = "%s/%s" % (VAGRANT_HOME, '.vagrant')
    has_dot_vagrant = os.path.exists(dot_vagrant)
    if not has_dot_vagrant:
        print "Initializing Vagrant in %s/ ..." % (VAGRANT_HOME)
        with settings(
            hide('warnings', 'running', 'stdout', 'stderr'),
            warn_only=True
        ):
            with lcd(SPRINTLY_HOME):
                local ("vagrant init", capture=True)


    vagrantfile = "%s/%s" % (VAGRANT_HOME, 'Vagrantfile')
    has_vagrantfile = os.path.exists(vagrantfile)
    if not has_vagrantfile:
        print "creating Vagrantfile in %s" % vagrantfile
        template = """
# -*- mode: ruby -*-
# vi: set ft=ruby :

Vagrant::Config.run do |config|
  # Every Vagrant virtual environment requires a box to build off of.
  config.vm.box = "sprintly"

  # Assign this VM to a host-only network IP, allowing you to access it
  # via the IP. Host-only networks can talk to the host machine as well as
  # any other machines on the same network, but cannot be accessed (through this
  # network interface) by any external networks.
  config.vm.network :hostonly, "33.33.33.10"
  config.vm.host_name = '%s'

  config.vm.share_folder "SPRINTLY_HOME", "/var/sprint.ly", "#{ENV['SPRINTLY_HOME']}"

  # Forward a port from the guest to the host, which allows for outside
  # computers to access the VM, whereas host only networking does not.
  config.vm.forward_port 80, 8080
  #
  user = ENV['OPSCODE_USER'] || ENV['USER']
  base_box = ENV['VAGRANT_BOX'] || 'sprintly'

  # The Opscode Platform uses HTTPS. Substitute your organization for
  # ORGNAME in the URL and validation key.
  #
  # If you have your own Chef Server, use the appropriate URL, which may be
  # HTTP instead of HTTPS depending on your configuration. Also change the
  # validation key to validation.pem.
  #
  config.vm.provision :chef_client do |chef|
    chef.chef_server_url = "https://api.opscode.com/organizations/sprintly-aws"
    # get these values from your chef/.chef/knife.rb file
    chef.validation_key_path = "#{ENV['SPRINTLY_HOME']}/../chef/.chef/sprintly-aws-validator.pem"
    chef.validation_client_name = "sprintly-aws-validator"

    chef.provisioning_path = "/etc/chef"

    chef.log_level = :info
    chef.environment = "sprintly_dev"

    chef.add_role('sprintly_vagrant_vm')
  end
end
"""
        vagrantfilecontents = template % "sprintly-appserver-vm-%s" % os.environ['USER']
        with open(vagrantfile, 'w') as vf:
            vf.write(vagrantfilecontents)

    print "All done! Run 'vagrant up' to bring up your Sprint.ly dev instance."