To Grasp the Cloud—Fundamental Concepts - Deploying and Managing a Cloud Infrastructure - page 33

running on the cloud from a few users to hundreds of millions of users. Let's consider the
example of Snapchat.
Back in November 2013, Snapchat had 30 full-time employees, which included develop-
ers, managers, and business development staff. It was reportedly managing a throughput
of 350 million photos through the app on daily basis. That is a tall order. If you compute
just the data storage requirements for running such a massive operation, there is no way
a team of 30 people—out of which probably not more than 3 or 4 would be handling the
cloud infrastructure—would have managed to keep the application running at this scale
10 years ago. And Snapchat scaled very quickly, from a few thousand users to reportedly
50 million users by January 2014.
The cloud has been an enabler for a plethora of business, productivity, social, and what-
not verticals. The promise of availability of unlimited server resources when you need them
is one of the cornerstones of cloud computing. For cloud providers, this means economy of
scale, which translates into the requirement for building and operating massive data centers
and hundreds of thousands of servers.
The Cloud Hypervisor
Hypervisors are the software, firmware, or hardware that manage the complete life cycle
of a virtual machine (VM), including creating, monitoring usage, and deletion. In the
following section, we will dive deeper into virtualization technology, including types,
use cases, real-world examples, and benefits.
Type 1 and Type 2
Before we talk about the types of virtualizations, let's revisit the concept. Virtualization
allows for packing multiple OS instances on the same hardware, running indepen-
dently with different software stacks. Gerald J. Popek and Robert P. Goldberg, in their
1974 article “Formal Requirements for Virtualizable Third Generation Architectures”
( Communications of the ACM , 1974), classified hypervisors into two main types.
Figure 2.1 explains where two different types of virtualization fit within the whole
hardware and software stack.
Type 1 Also called native or bare metal hypervisors, they run directly on the host's hard-
ware and control it. Type 1 hypervisors also manage guest operating systems. Examples
include Oracle VM Server, Citrix XenServer, and Microsoft Hyper-V.
Type 2 Also called hosted hypervisors, they run atop a host operating system already
running on the hardware. Type 2 hypervisors constitute a distinct second layer of soft-
ware atop host operating systems. They manage and run guest operating systems at the
third layer from the hardware. Examples include VMware Workstation and Oracle VM
VirtualBox.