Override Vagrant configuration settings locally (per-dev)

Question

The Vagrantfile is just Ruby, so YAML is another option.

For example, in the Vagrantfile I do this:

# -*- mode: ruby -*-
# vi: set ft=ruby :
require 'yaml'

settings = YAML.load_file 'vagrant.yml'
db_ip_address = settings['db']['ip_address']
api_ip_address = settings['api']['ip_address']

Vagrant.configure("2") do |config|
  config.vm.box = "ffuenf/ubuntu-13.10-server-amd64"
  config.vm.box_url = "https://vagrantcloud.com/ffuenf/ubuntu-13.10-server-amd64/version/4/provider/virtualbox.box"

  config.vm.define "db" do |db|
    db.vm.synced_folder settings['db']['artifacts_dir']['host'], settings['db']['artifacts_dir']['guest']
    db.vm.network "private_network", ip: db_ip_address
    ... other stuff ...
  end

  config.vm.define "api" do |api|
    api.vm.synced_folder settings['api']['artifacts_dir']['host'], settings['api']['artifacts_dir']['guest']
    api.vm.network "private_network", ip: api_ip_address
    api.vm.network "forwarded_port", guest: settings['api']['forwarded_port']['guest'], host: settings['api']['forwarded_port']['host']
  end
end

Then I have a vagrant.yml file (I just made up the name; you can use whatever name you like) for the developer-specific configuration:

db:
  ip_address: 192.168.4.14
  artifacts_dir:
    host: /Users/willie/myapp/db-scripts
    guest: /opt/myapp/db

api:
  ip_address: 192.168.4.15
  forwarded_port:
    host: 9080
    guest: 8080
  artifacts_dir:
    host: /Users/willie/myapp/artifacts
    guest: /opt/myapp/api

I would suggest using environment variables to dynamically change the behavior of the Vagrantfile without editing the file itself.

To give a real world example, here's how you could use an Ubuntu base box by default but have an environment variable define an alternative Linux distribution:

if ENV['OPERATINGSYSTEM']
  if ENV['OPERATINGSYSTEM'].downcase == 'redhat'
    os_name = 'centos'
    config.vm.box     = 'centos'
    config.vm.box_url = 'https://dl.dropbox.com/u/7225008/Vagrant/CentOS-6.3-x86_64-minimal.box'
  else
    raise(Exception, "undefined operatingsystem: #{ENV['OPERATINGSYSTEM']}")
  end
else
  os_name = 'precise64'
  config.vm.box     = 'precise64'
  config.vm.box_url = 'http://files.vagrantup.com/precise64.box'
end

This example comes from https://github.com/puppetlabs/puppetlabs-openstack_dev_env

If you are prepared to define settings that are applied to all your vagrant boxes it's worth noting that, "Vagrant actually loads a series of Vagrantfiles, merging the settings as it goes." (ref https://docs.vagrantup.com/v2/vagrantfile/)

So I have the following defined in ~/.vagrant.d/Vagrantfile to increase the amount of RAM for my Vagrant boxes:

Vagrant.configure(2) do |config|
    config.vm.provider "virtualbox" do |vb|
      vb.memory = 2048
    end
end

Here's an idea. It may be "ugly" and "wrong", but, at least, it works :)

# file2.rb, this is your per-dev configuration file
puts "included external file which uses outer var: #{foo}"

# file1.rb, this would be your Vagrantfile
puts 'first'
foo = 'bar'

external = File.read 'file2.rb'
eval external
puts 'second'

Let's run that

$ ruby file1.rb
first
included external file which uses outer var: bar
second

Adapting to your example, file2.rb would contain only usage of config without defining it (config will be provided from outer context)

  config.vm.provision :puppet do |puppet|
    puppet.facter = { "proxy" => "proxy.host:80" }
  end

And your Vagrant file may look like this:

Vagrant::Config.run do |config|
  external = File.read 'Vagrantfile.local'
  eval external

  # proceed with general settings here
  config.vm.provision :puppet do |puppet|
    puppet.facter = { "proxy" => "proxy.host:80" }
  end
end

Update (another, "data-driven" approach)

# Vagranfile.local
config_values[:puppet][:facter][:proxy] = 'proxy.host:80'

# Vargantfile
Vagrant::Config.run do |config|
  config_values = {
    puppet: {
      facter: {
        proxy: nil
      },
      manifests_file: 'my_manifest.pp'

    }
  }
  external = File.read 'Vagrantfile.local'
  eval external # this should overwrite proxy config

  # proceed with general settings here
  config.vm.provision :puppet do |puppet|
    if config_values[:puppet][:facter][:proxy]
      puppet.facter = { "proxy" => config_values[:puppet][:facter][:proxy] } 
    end

    puppet.manifests_file = config_values[:puppet][:manifests_file]
  end
end

I believe that's the exact use case that Nugrant plugin was created to solve. It allows each of your devs to have a .vagrantuser (which is a .gitignore-ed file) in YAML specifying custom configuration values then reference these values with ease in Vagrantfile.

In your case, a proxied developer would have their .vagrantuser file looking like this:

proxy: 'proxy.host:80'

And your Vagrantfile would look like this (pseudo code, I don't really know ruby):

Vagrant::Config.run do |config|
  config.vm.provision :puppet do |puppet|
    if config.user.has_key?('proxy')
      puppet.facter = { "proxy" => config.user.proxy }
    end
  end
end

You should bundle a sample/reference vagrantuser (i.e. vagrantuser.example) file for your devs to copy and adjust to their environment.