What is Virtualization?

INFO 153B/253B: Backend Web Architecture

Kay Ashaolu

You hear about virtual machines, containers, docker and other stuff

• What does all of this mean?
• And how does it help what we have been working on?

Let's start from the beginning

• What we have been doing from the start
• We have been running servers applications on can be considered "bare metal"
• What does that really mean?

Bare metal = your computer

• Your computer contains a computer chip, RAM, a disk drive, and some other wiring to make it all work together
• This is the "bare metal"
• You have an operating system installed on top of your computer, typically Mac OS X, Windows, or Linux

Before Virtualization

• "In a world before virtualization, servers would traditionally run one application on one server with one operating system. In the old system, the number of servers would continue to mount since every new app required its own server and operating system"
• Each server would use only 12% of it's resources

Why not run multiple apps on a single box

• We can do this by simply running multiple Flask applications on a single computer
• Each application could have its own port
• They could communicate with each other

Security and Performance

• Imagine if you can't access your database because the web server that you hosted on the same computer was being overloaded
• That wouldn't be a good situation, nor would it be very easy to figure out
• Also imagine if your web server that is connected to the public internet got hacked. Now they are in your database as well
• In addition, each application typically requires different levels of resources (CPU, RAM, Disk space) for optimum performance

After Virtualization

• We now have the ability to build mutliple "virtual machines" on top of our a single "bare metal" server
• Virtual Machines  can have their own operating system with their own applications installed inside of it
• Now we can run multiple isolated applications within the same bare metal server.
• How is this possible?

The Hypervisor

• Software layer that provides the API for VMs to access computer resources
• Hypervisor can distribute underlying resources that VM needs
• Hypervisor can be installed on "bare metal" or on top of an operating system 
• Now you can have multiple operating systems running multiple applications on the same box

Some Terminology

• Bare Metal: Your physical machine
• Virtual Machine (VM): Emulation of a real computer that executes real computer programs. Also emulates drivers and RAM and hard disk and lso on
• Hypervisor: Piece of software, firmware, or hardware that VMs run on top of. Provides API for VMs to interact with "bare metal"

Some Terminology

• Host Machine: Machine that provdes VMs with resources
• Guest Machine: Virtual Machine that has been created on a guest machine 

Hosted vs Bare Metal

Hosted Hypevisor:

• Runs on top of an existing operating system of the host machine
• VM's don't have direct access to computer's resources: must ask OS
• Pro: Cross-Compatbility 
• Con: Performance

Bare metal Hypervisor:

• Runs directly on the computer: no operating system required
• Through this hypervisor VMs have direct access to computer's resources
• Pro: Performance
• Con: Cross-Compatibility

VM Stack

Alright, so what is a Container?

• Now that we have specifically defined what a VM is, now we can talk about containers
• A VM virtualizes hardware : as if you are running a separate machine ("guest machine") with distinct RAM, CPU, Memory, and so on
• A Container provides operating system level virtualization. 
• Key difference is that a Container does not abstract hardware elements such as CPU, RAM, and disk space

Containers vs VMs

• Big difference: Containers share the host system, or OS. Each container has their separate "user-space" to run

Benefits of Containers

• Remember the goal is to run multiple isolated applications on the same hardware
• VMs provide that but requires an operating system installed on each computer
• That takes more resources especially if you are 1) running the same OS and 2) just want to run more applications
• Containers essentially share the same OS accross all of them but are still isolated

Questions?