Vagrant is a handy and easy-to-use Virtual Machine tool that can be used within your command-line interface. In a nutshell, it makes it easy to create and configure lightweight, reproducible developer environments.

In this mini course, you will learn all about virtualization. You will learn how to set up a Vagrant environment, build your own VM, as well as Vagrant commands which you can use from the command line.

In the latter half of the course, you will learn how to work with vagrantfile, networking, and data sharing. In all, this is your crash course for understanding the fundamentals of Vagrant.

A Guide to Vagrant and Virtual Machines

# What are multi-machine VMs and why do we need them?

Vagrant is able to define and control multiple guest machines per Vagrantfile. This is known as a `"multi-machine"` environment.

These machines are generally able to work together or are somehow associated with each other. Here are some use cases describing what people are using multi-machine environments for today:

1. Accurately modeling a multi-server production topology, such as separating a web and database server.
2. Modeling a distributed system and how they interact with each other.
3. Testing an interface, such as an API, to a service component.
4. Disaster-case testing: machines dying, network partitions, slow networks, inconsistent world views, etc.

We can also use multi-machine VMs to play around with Ansible. 

In this chapter, we'll be looking at how you can build and run multi-machine Vagrant VMs. 

# Build a multi-machine Vagrant VM.

Let's start off with just one machine Vagrantfile.
```
Vagrant.configure("2") do |config|
  config.vm.box = "centos/7"
end
```

We can use the `config.vm.define` method in the `Vagrantfile` to create multi-machine VMs.
```
config.vm.define "node1" do |node1|
```
Here, `node1` is the name of the VM, however, the name can be anything.

Let's provide a box, or an image, to our VM `node1` using the `vm.box` file. Moreover, let’s assign it a hostname using the `node1.vm.hostname` file.
```
config.vm.define "node1" do |node1|
    node1.vm.box = "ubuntu/trusty64"
    node1.vm.hostname = "webserver"
  end
```
Similarly, we can add a second VM, `node2`, in our `Vagrantfile` as shown below.
```
config.vm.define "node2" do |node2|
    node2.vm.box = "centos/7"
    node2.vm.hostname = "database"
  end
```
Then, put it all together.
```
Vagrant.configure("2") do |config|
  
  config.vm.define "node1" do |node1|
    node1.vm.box = "ubuntu/trusty64"
    node1.vm.hostname = "webserver"
  end

  config.vm.define "node2" do |node2|
    node2.vm.box = "centos/7"
    node2.vm.hostname = "database"
  end
end
```

Now, when starting up with `vagrant up`, both 2 machines will get started. Now, do the `vagrant status` to check the status of your machines.

You can `ssh` into an individual machine by specifying its `hostname`.
```
vagrant ssh webserver
```

You can also specify your primary machine, in case you haven’t already, by adding `primary: true` in the Vagrantfile as shown below.
```
Vagrant.configure("2") do |config|
  
  config.vm.define "node1", primary: true do |node1|
    node1.vm.box = "ubuntu/trusty64"
    node1.vm.hostname = "webserver"
  end
 
  config.vm.define "node2" do |node2|
    node2.vm.box = "centos/7"
    node2.vm.hostname = "database"
  end
end
```

We’ve added `primary: true` against the node1 VM. Now, if the VM hostname is not specified during `vagrant ssh <vm-name>`, you’ll get logged into node1 by default.

## Conclusion
Congratulations on completing this course. The next step would be to learn some automation tools, like Ansible or chef, and use that technology with Vagrant. All of this will prepare you for your journey towards DevOps. 

The last section in this course provides an assessment and a lab session. 

In this lesson, we’ll be looking at how you can build and run multi-machine Vagrant VMs.

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Multi-Machine VMs With Vagrant

What are multi-machine VMs and why do we need them?