My global Vagrant configuration (~/.vagrant.d/Vagrantfile)

Vagrantfile

# URI of the local (caching) HTTP proxy
LOCAL_HTTP_PROXY = 'http://192.168.33.200:8123'

# Configures vagrant-cachier and vagrant-proxyconf.
# Should be called only on "local machine" providers.
def configure_caching(config)
  if Vagrant.has_plugin?('vagrant-cachier')
    config.cache.enable_nfs = true
    config.cache.enable :gem
    config.cache.enable :npm
  end

  if Vagrant.has_plugin?('vagrant-proxyconf')
    config.proxy.http     = LOCAL_HTTP_PROXY
    config.proxy.https    = LOCAL_HTTP_PROXY
    config.proxy.no_proxy = 'localhost,127.0.0.1'
  end
end

Vagrant.configure('2') do |config|
  config.vm.provider :virtualbox do |vbox, override|
    configure_caching(override)
    vbox.memory = 512
  end

  config.vm.provider :vmware_fusion do |fusion, override|
    configure_caching(override)
    fusion.vmx['memsize'] = 512
  end

  config.vm.provider :aws do |aws, override|
    aws.access_key_id        = ENV['AWS_ACCESS_KEY']
    aws.secret_access_key    = ENV['AWS_SECRET_KEY']
    aws.keypair_name         = ENV['USER']

    aws.region               = 'us-east-1'
    aws.instance_type        = 't1.micro'
    aws.security_groups      = ['default']

    override.ssh.private_key_path = "#{ENV['HOME']}/.ssh/id_rsa"
  end

  config.vm.provider :digital_ocean do |ocean, override|
    ocean.client_id          = ENV['DIGITAL_OCEAN_CLIENT_ID']
    ocean.api_key            = ENV['DIGITAL_OCEAN_API_KEY']
    ocean.ssh_key_name       = ENV['USER']

    ocean.region             = 'New York 1'
    ocean.size               = '512MB'

    override.ssh.private_key_path = "#{ENV['HOME']}/.ssh/id_rsa"
  end
end