Using files from /vagrant as /var/www

default.rb

# Create /var/www directory.
directory "/var/www" do
  owner "www-data"
  group "www-data"
  mode "0755"
  action :create
  not_if "mountpoint /var/www" # Not if already mounted
end

# Mount /var/www directory.
mount "/var/www" do
  device "/vagrant/www" # I keep my site files in a "www" subfolder, so I mount that
  fstype "nfs"
  options ["rw", "bind"]
  action [:mount, :enable]
end

Vagrantfile

Vagrant::Config.run do |config|

  (…)

  # Share project folder through NFS.
  config.vm.share_folder("v-root", "/vagrant", ".", :nfs => true)

  # Provisioning.
  config.vm.provision :chef_solo do |chef|
    chef.cookbooks_path = "cookbooks"
    chef.add_recipe("vagrant_main")
  end

  (…)

end

Override of config.vm.share_folder to use NFS is recommended and (I think) required for the mount in default.rb to work.

UPDATE! Turns out the "mount --bind" technique used here gives horrible performance when many files are loaded, which is typical for CMS solutions, in my case Drupal. XHProf showed 2 (up to 3) times longer wall time with a bound mount compared to reading from the original /vagrant directory. You'll want to set your web server to fetch web files from the /vagrant directory instead.

A neat solution is to share the project folder through NFS to /srv on the box:

config.vm.share_folder("v-root", "/srv", ".", :nfs => true)

That way you can use /srv/www (being vagrant_project_dir/www), which is an alternative to /var/www in Linux. Just point your vhost files there, et voilà.