The purpose is to have several VM to reproduct production environment, simulate network failure. We start simply with a web machine and an external database (and specific disk size for that)

Install vagrant plugins

vagrant plugin install vagrant-vbguest
vagrant plugin install vagrant-disksize

Create your multi machine environment

cd {yourdir}/workspace/envdev/
mkdir my-multi-machine
cd my-multi-machine
vagrant init
...

Edit your Vagrantfile

Vagrant.configure("2") do |config|
	# WEB
	config.vm.define "web", primary: true do |web|
		web.vm.box = "debian/stretch64"
		web.vm.box_check_update = false
		web.vm.network "private_network", ip: "192.168.33.101"
		web.vm.synced_folder ".", "/vagrant", owner: "vagrant", group: "vagrant", type: "virtualbox"
		web.vm.synced_folder "../../", "/home/vhosts", owner: "vagrant", group: "vagrant", type: "virtualbox"
		web.vm.provider "virtualbox" do |vb|
			vb.customize ["modifyvm", :id, "--name", "web"]
			vb.customize ["modifyvm", :id, "--memory", "512"]
			vb.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
			vb.customize ["modifyvm", :id, "--natdnsproxy1", "on"]
	  	end
	end
	# DB
	config.vm.define "db" do |db|
		db.vm.box = "debian/stretch64"
		db.disksize.size = "30GB"
		db.vm.box_check_update = false
		db.vm.network "private_network", ip: "192.168.33.102"
		db.vm.synced_folder ".", "/vagrant", owner: "vagrant", group: "vagrant", type: "virtualbox"
		db.vm.provider "virtualbox" do |vb|
			vb.customize ["modifyvm", :id, "--name", "db"]
			vb.customize ["modifyvm", :id, "--memory", "512"]
			vb.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
			vb.customize ["modifyvm", :id, "--natdnsproxy1", "on"]
  		end
	end
end

“web” machine is the primary. When you vagrant ssh, you enter in it automatically. So to go in db, enter vagrant ssh db

More

Read the doc

DNS

If you want to get name (name.local)
Set {subconfig}.vm.hostname = "myname" and install apt-get install -y avahi-daemon libnss-mdns.

You can ping any other VM by using their hostname (plus .local at the end)