The document provides an in-depth overview of virtualization technology, including CPU, memory, and I/O virtualization, highlighting how virtualization allows multiple virtual machines to run on a single physical machine. It examines the complexities of managing virtual environments and introduces Amazon EC2 as a case study for scalable computing in the cloud. Additionally, it discusses software-defined networking (SDN) as a flexible approach to manage network traffic and resources, enhancing control and security over traditional networking methods.

1. Unit III:
Virtualization
MARK AJ L. CASPILLO
Instructor

2. Virtualization
is technology that you can use to create virtual
representations of servers, storage, networks,
and other physical machines. Virtual software
mimics the functions of physical hardware to run
multiple virtual machines simultaneously on a
single physical machine.

3. VIRTUALIZATION OF CPU, MEMORY, AND I/O DEVICES
1. Hardware Support for Virtualization
Modern operating systems and processors permit multiple
processes to run simultaneously. If there is no protection mechanism in a
processor, all instructions from different processes will access the
hardware directly and cause a system crash. Therefore, all processors
have at least two modes, user mode and supervisor mode, to ensure
controlled access of critical hardware. Instructions running in supervisor
mode are called privileged instructions. Other instructions are
unprivileged instructions. In a virtualized environment, it is more difficult
to make OSes and applications run correctly because there are more
layers in the machine stack.

5. 2. CPU Virtualization
A VM is a duplicate of an existing computer system in
which a majority of the VM instructions are executed on
the host processor in native mode. Thus, unprivileged
instructions of VMs run directly on the host machine for
higher efficiency. Other critical instructions should be
handled carefully for correctness and stability. The
critical instructions are divided into three
categories: privileged instructions, control-sensitive
instructions, and behavior-sensitive instructions.

6. • Privileged instructions execute in a privileged mode
and will be trapped if executed outside this mode.
• Control-sensitive instructions attempt to change the
configuration of resources used.
• Behavior-sensitive instructions have different
behaviors depending on the configuration of resources,
including the load and store operations over the virtual
memory.
The Critical Instructions

7. A CPU architecture is virtualizable if it supports the ability
to run the VM’s privileged and unprivileged instructions in
the CPU’s user mode while the VMM runs in supervisor
mode. When the privileged instructions including control-
and behavior-sensitive instructions of a VM are exe-cuted,
they are trapped in the VMM. In this case, the VMM acts
as a unified mediator for hardware access from different
VMs to guarantee the correctness and stability of the
whole system.

8. 2.1 Hardware-Assisted CPU Virtualization
This technique attempts to simplify virtualization because
full or paravirtualization is complicated. Intel and AMD
add an additional mode called privilege mode level
(some people call it Ring-1) to x86 processors.
Therefore, operating systems can still run at Ring 0 and
the hypervisor can run at Ring -1. All the privileged and
sensitive instructions are trapped in the hypervisor
automatically. This technique removes the difficulty of
implementing binary translation of full virtualization. It
also lets the operating system run in VMs without
modification.

10. Memory Virtualization
Virtual memory virtualization is similar to the virtual memory support
provided by modern operat-ing systems. In a traditional execution
environment, the operating system maintains mappings of virtual
memory to machine memory using page tables, which is a one-stage
mapping from virtual memory to machine memory. All modern x86 CPUs
include a memory management unit (MMU) and a translation lookaside
buffer (TLB) to optimize virtual memory performance. However, in a
virtual execution environment, virtual memory virtualization involves
sharing the physical system memory in RAM and dynamically allocating it
to the physical memory of the VMs.

12. I/O Virtualization
I/O virtualization involves managing the routing of I/O
requests between virtual devices and the shared
physical hardware. At the time of this writing, there are
three ways to implement I/O virtualization: full device
emulation, para-virtualization, and direct I/O. Full device
emulation is the first approach for I/O virtualization.
Generally, this approach emulates well-known, real-
world devices.

13. All the functions of a device or bus infrastructure, such as device
enumeration, identification, interrupts, and DMA, are replicated in software.
This software is located in the VMM and acts as a virtual device. The I/O
access requests of the guest OS are trapped in the VMM which interacts
with the I/O devices.

14. A single hardware device can be shared by multiple VMs that run
concurrently. However, software emulation runs much slower than
the hardware it emulates [10,15]. The para-virtualization method of
I/O virtualization is typically used in Xen. It is also known as the
split driver model consisting of a frontend driver and a backend
driver. The frontend driver is running in Domain U and the backend
dri-ver is running in Domain 0. They interact with each other via a
block of shared memory. The frontend driver manages the I/O
requests of the guest OSes and the backend driver is responsible
for managing the real I/O devices and multiplexing the I/O data of
different VMs. Although para-I/O-virtualization achieves better
device performance than full device emulation, it comes with a
higher CPU overhead.

15. Direct I/O virtualization lets the VM access devices directly. It can achieve
close-to-native performance without high CPU costs. However, current
direct I/O virtualization implementations focus on networking for
mainframes. There are a lot of challenges for commodity hardware
devices. For example, when a physical device is reclaimed (required by
workload migration) for later reassign-ment, it may have been set to an
arbitrary state (e.g., DMA to some arbitrary memory locations) that can
function incorrectly or even crash the whole system. Since software-
based I/O virtualization requires a very high overhead of device
emulation, hardware-assisted I/O virtualization is critical. Intel VT-d
supports the remapping of I/O DMA transfers and device-generated
interrupts. The architecture of VT-d provides the flexibility to support
multiple usage models that may run unmodified, special-purpose, or
“virtualization-aware” guest OSes.

16. Case Study: Amazon EC2
Amazon Elastic Compute Cloud (Amazon EC2) provides
scalable computing capacity in the Amazon Web Services
(AWS) cloud. Using Amazon EC2 eliminates your need to invest
in hardware up front, so you can develop and deploy
applications faster. You can use Amazon EC2 to launch
as many or as few virtual servers as you need, configure
security and networking, and manage storage. Amazon EC2
enables you to scale up or down to handle changes in
requirements or spikes in popularity, reducing
your need to forecast traffic.

17. Amazon EC2 is a central part of AWS:
Amazon Elastic Compute Cloud (EC2) forms a central part
of Amazon.com's cloud-computing platform, Amazon Web Services
(AWS) by allowing users to rent virtual computers on which to run
their own computer applications. EC2 encourages scalable
deployment of applications by providing a web service through
which a user can boot an Amazon Machine Image (AMI) to
configure a virtual machine, which Amazon calls an "instance",
containing any software desired. A user can create, launch, and
terminate server-instances as needed, paying by the second for
active servers – hence the term "elastic". EC2 provides users with
control over the geographical location of instances that allows for
latency optimization and high levels of redundancy.

18. 2) Instance types:
Initially, EC2 used Xen virtualization exclusively. However,
on November 6, 2017, Amazon announced the new C5
family of instances that were based on a custom
architecture around the KVM hypervisor, called Nitro. Each
virtual machine, called an "instance", functions as a virtual
private server. Amazon sizes instances based on "Elastic
Compute Units". The performance of otherwise identical
virtual machines may vary. On November 28, 2017, AWS
announced a bare-metal instance type offering marking a
remarkable departure from exclusively offering virtualized
instance types

19. As of January 2019, the following instance types were offered:
General Purpose: A1, T3, T2, M5, M5a, M4, T3a
Compute Optimized: C5, C5n, C4
Memory Optimized: R5, R5a, R4, X1e, X1, High Memory, z1d
Accelerated Computing: P3, P2, G3, F1
Storage Optimized: H1, I3, D2
As of April 2018, the following paying method for instance were offered:
On-demand: pay by the hour without commitment.
Reserved: rent instances with one-time payment receiving discounts
on the hourly charge.
Spot: bid-based service: runs the jobs only if the spot price is below
the bid specified by bidder. The spot price is claimed to be supply-
demand based, however a 2011 study concluded that the price was
generally not set to clear the market, but was dominated by an
undisclosed reserve price

20. 3) Cost:
As of April 2018, Amazon charged about $0.0058/hour
($4.176/month) for the smallest "Nano Instance" (t2.nano)
virtual machine running Linux or Windows. Storage-
optimized instances cost as much as $4.992/hour
(i3.16xlarge). "Reserved" instances can go as low as
$2.50/month for a three-year prepaid plan. The data transfer
charge ranges from free to $0.12 per gigabyte, depending
on the direction and monthly volume (inbound data transfer
is free on all AWS services)

21. (4) Free tier:
As of December 2010, Amazon offered a bundle
of free resource credits to
new account holders. The credits are designed
to run a "micro" sized server,
storage (EBS), and bandwidth for one year.
Unused credits cannot be carried
over from one month to the next

22. 5) Reserved instances:
Reserved instances enable EC2 or RDS service users to reserve an
instance for one or three years. The corresponding hourly rate
charged by Amazon to operate the instance is 35-75% lower than the
rate charged for on-demand instances. Reserved Instances can be
purchased in three different ways: All Upfront, Partial Upfront and No
Upfront. The different purchase options allow for different structuring
of payment models. In September 2016, AWS announced several
enhancements to Reserved Instances, introducing a new
feature called scope and a new reservation type called a Convertible.
In October 2017, AWS announced the allowance to subdivide the
instances purchased for more flexibility

23. 6) Spot instances:
Cloud providers maintain large amounts of excess capacity
they have to sell or risk incurring losses. Amazon EC2 Spot
instances are spare compute capacity in the AWS cloud
available at up to 90% discount compared to On-
Demand prices. As a trade-off, AWS offers no SLA on these
instances and customers take the risk that it can be
interrupted with only two minutes of notification when
Amazon needs the capacity back. Researchers from the
Israeli Institute of Technology found that "they (Spot
instances) are typically generated at random from within a
tight price interval via a dynamic hidden reserve price". Some
companies, like Spotinst, are using big data combined
with machine learning to predict spot interruptions up to 15
minutes in
Advance.

24. 7) Saving plans:
In November 2019, Amazon announced Savings Plans. Savings Plans are an
alternative to Reserved Instances that come in 2 different plan types:
Compute Savings Plans and EC2 Instances Savings Plans. Compute Savings
Plans allow an organisation to commit to EC2 and Fargate usage with the
freedom to change region, family, size, availability zone, OS and tenancy
inside the lifespan of the commitment. EC2 Instance Savings plans provide
the lowest prices but are less flexible meaning a user must commit to
individual instance families within a region to take advantage, but with the
freedom to change instances within the family in that region.

25. 8) Features of EC2:
Amazon EC2 provides the following features:
Virtual computing environments, known as instances
Preconfigured templates for your instances, known as Amazon
Machine
Images (AMIs), that package the bits you need for your server (including
the operating system and additional software)
Various configurations of CPU, memory, storage, and networking
capacity for your instances, known as instance types
Secure login information for your instances using key pairs (AWS
stores
the public key, and you store the private key in a secure place)
Storage volumes for temporary data that's deleted when you stop or
terminate your instance, known as instance store volumes

26. Persistent storage volumes for your data using Amazon Elastic Block
Store (Amazon EBS), known as Amazon EBS volumes
Multiple physical locations for your resources, such as instances and
Amazon EBS volumes, known as Regions and Availability Zones
A firewall that enables you to specify the protocols, ports, and source IP
ranges that can reach your instances using security groups
Static IPv4 addresses for dynamic cloud computing, known as Elastic IP
addresses
Metadata, known as tags, that you can create and assign to your Amazon
EC2 resources
Virtual networks you can create that are logically isolated from the rest of
the AWS cloud, and that you can optionally connect to your own network,
known as virtual private clouds (VPCs)

27. 9) Limits of EC2:
AWS defines certain limits by default, to prevent users from accidentally
creating too many resources. Your AWS account may reach one or more of
these limits when using a large number of servers, backups or static IP
addresses.
EC2 Instances
By default, AWS has a limit of 20 instances per region. This includes all
instances set up on your AWS account.
To increase EC2 limits, request a higher limit by providing information
about the new limit and regions where it should be applied.

28. Static IP Addresses
By default, AWS sets a limit of 5 static IP addresses per region. This
includes IP addresses unassigned and currently assigned to a server.
To increase IP addresses limit, request a higher limit by providing
information about the new limit and regions where it should be applied.
Snapshots
The AWS default limit for all snapshots is 10000 snapshots per region.
To increase the number of snapshots allowed, contact AWS Support and
request a higher limit.
Other Limits
If your AWS account reaches any of AWS’ other limits, contact AWS
Support and request a higher limit.

29. What is Software-Defined Networking
(SDN)
Software-Defined Networking (SDN) is an approach to networking that
uses software-based controllers or application programming interfaces (APIs)
to communicate with underlying hardware infrastructure and direct traffic on a
network.
This model differs from that of traditional networks, which use dedicated
hardware devices (i.e., routers and switches) to control network traffic. SDN
can create and control a virtual network – or control a traditional hardware –
via software.

30. Why Software-Defined Networking is important?
SDN represents a substantial step forward from traditional
networking, in that it enables the following:
•Increased control with greater speed and flexibility: Instead of
manually programming multiple vendor-specific hardware devices,
developers can control the flow of traffic over a network simply by
programming an open standard software-based controller.
Networking administrators also have more flexibility in choosing
networking equipment, since they can choose a single protocol to
communicate with any number of hardware devices through a
central controller.

31. •Customizable network infrastructure: With a software-defined
network, administrators can configure network services and allocate
virtual resources to change the network infrastructure in real time through
one centralized location. This allows network administrators to optimize
the flow of data through the network and prioritize applications that require
more availability.
•Robust security: A software-defined network delivers visibility into the
entire network, providing a more holistic view of security threats. With the
proliferation of smart devices that connect to the internet, SDN offers clear
advantages over traditional networking. Operators can create separate
zones for devices that require different levels of security, or immediately
quarantine compromised devices so that they cannot infect the rest of the
network.

32. How does Software-Defined Networking (SDN) work?
In SDN (like anything virtualized), the software is decoupled from the hardware.
SDN moves the control plane that determines where to send traffic to software,
and leaves the data plane that actually forwards the traffic in the hardware. This
allows network administrators who use software-defined networking to program
and control the entire network via a single pane of glass instead of on a device
by device basis.
There are three parts to a typical SDN architecture, which may be located in
different physical locations:
Applications, which communicate resource requests or information about the
network as a whole
Controllers, which use the information from applications to decide how to route
a data packet
Networking devices, which receive information from the controller about
where to move the data

33. Benefits of Software-Defined Networking (SDN)
Many of today’s services and applications, especially when they
involve the cloud, could not function without SDN. SDN allows
data to move easily between distributed locations, which is critical
for cloud applications.

34. SDN supports moving workloads around a network quickly. For
instance, dividing a virtual network into sections, using a technique
called network functions virtualization (NFV), allows
telecommunications providers to move customer services to less
expensive servers or even to the customer’s own servers. Service
providers can use a virtual network infrastructure to shift workloads
from private to public cloud infrastructures as necessary, and to make
new customer services available instantly. SDN also makes it easier
for any network to flex and scale as network administrators add or
remove virtual machines, whether those machines are on-premises or
in the cloud.

35. What are the different models of SDN?
While the premise of centralized software controlling the flow of data in switches
and routers applies to all software-defined networking, there are different models
of SDN.
•Open SDN: Network administrators use a protocol like OpenFlow to control the
behavior of virtual and physical switches at the data plane level.
•SDN by APIs: Instead of using an open protocol, application programming
interfaces control how data moves through the network on each device.

36. •SDN Overlay Model: Another type of software-defined networking runs a
virtual network on top of an existing hardware infrastructure, creating dynamic
tunnels to different on-premise and remote data centers. The virtual network
allocates bandwidth over a variety of channels and assigns devices to each
channel, leaving the physical network untouched.
•Hybrid SDN: This model combines software-defined networking with traditional
networking protocols in one environment to support different functions on a
network. Standard networking protocols continue to direct some traffic, while
SDN takes on responsibility for other traffic, allowing network administrators to
introduce SDN in stages to a legacy environment.