How to configure the Vagrant virtual machine to use a specific proxy

Configure the Vagrant virtual machine to use a specific proxy using the vagrant-proxyconf plugin.

Install vagrant-proxyconf plugin.

$ vagrant plugin install vagrant-proxyconf

Installing the 'vagrant-proxyconf' plugin. This can take a few minutes...
Fetching vagrant-libvirt-0.1.2.gem
Fetching vagrant-proxyconf-2.0.10.gem
Parsing documentation for vagrant-libvirt-0.1.2
Installing ri documentation for vagrant-libvirt-0.1.2
Parsing documentation for vagrant-scp-0.1.0
Parsing documentation for vagrant-proxyconf-2.0.10
Installing ri documentation for vagrant-proxyconf-2.0.10
Done installing documentation for vagrant-libvirt, vagrant-scp, vagrant-proxyconf after 0 seconds
Successfully uninstalled fog-core-1.43.0

List installed plugins.

$ vagrant plugin  list

vagrant-libvirt (0.0.45, system)
vagrant-proxyconf (2.0.10, global)
vagrant-scp (0.1.0, global)

Use this plugin to define proxy inside Vagrantfile.

# -*- mode: ruby -*-
# vi: set ft=ruby :
Vagrant.configure("2") do |config|
  if Vagrant.has_plugin?("vagrant-proxyconf")
    config.proxy.http     = "http://192.168.0.1:3128/"
    config.proxy.https    = "http://192.168.0.1:3128/"
    config.proxy.no_proxy = "localhost,127.0.0.1,.example.org"
  end
  config.vm.box = "debian/buster64"
  config.vm.provider "virtualbox" do |vb|
     vb.memory = "1024"
   end
   config.vm.provision "shell", inline: <<-SHELL
     apt-get update
     apt-get install -y apache2
   SHELL
end

Alternatively, use environment variables.

$ VAGRANT_HTTP_PROXY="http://192.168.0.1:3128/" vagrant up