This Vagrantfile works with an external data file (a YAML file, named servers.yaml) to create multiple Vagrant boxes easily. The servers.yaml file contains all the specifics and can be easily edited to change the number and type of boxes to create. The Vagrantfile remains unchanged.

yaml-vagrantfile

# -*- mode: ruby -*-
# # vi: set ft=ruby :

# Specify minimum Vagrant version and Vagrant API version
Vagrant.require_version ">= 1.6.0"
VAGRANTFILE_API_VERSION = "2"

# Require YAML module
require 'yaml'

# Read YAML file with box details
servers = YAML.load_file('servers.yaml')

# Create boxes
Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|

  # Iterate through entries in YAML file
  servers.each do |servers|
    config.vm.define servers["name"] do |srv|
      srv.vm.box = servers["box"]
      srv.vm.network "private_network", ip: servers["ip"]
      srv.vm.provider :virtualbox do |vb|
        vb.name = servers["name"]
        vb.memory = servers["ram"]
      end
    end
  end
end