05-07-2012, 02:28 PM
VIRTUALIZATION DEFINED - EIGHT DIFFERENT WAYS
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Operating System Virtualization
The most prevalent form of virtualization today, virtual operating systems (or virtual machines) are quickly becoming a core component of the IT
infrastructure. Generally, this is the form of virtualization end-users are most familiar with. Virtual machines are typically full implementations of
standard operating systems, such as Windows Vista or RedHat Enterprise Linux, running simultaneously on the same physical hardware. Virtual
Machine Managers (VMMs) manage each virtual machine individually; each OS instance is unaware that 1) it’s virtual and 2) that other virtual
operating systems are (or may be) running at the same time. Companies like Microsoft, VMware, Intel, and AMD are leading the way in breaking
the physical relationship between an operating system and its native hardware, extending this paradigm into the data center. As the primary driving
force, data center consolidation is bringing the benefi ts of virtual machines to the mainstream market, allowing enterprises to reduce the number
of physical machines in their data centers without reducing the number of underlying applications. This trend ultimately saves enterprises money on
hardware, co-location fees, rack space, power, cable management, and more.
Application Server Virtualization
Application Server Virtualization has been around since the fi rst load balancer, which explains why “application virtualization” is often used as
a synonym for advanced load balancing. The core concept of application server virtualization is best seen with a reverse proxy load balancer: an
appliance or service that provides access to many different application services transparently. In a typical deployment, a reverse proxy will host a
virtual interface accessible to the end user on the “front end.” On the “back end,” the reverse proxy will load balance a number of different servers
and applications such as a web server. The virtual interface—often referred to as a Virtual IP or VIP—is exposed to the outside world, represents
itself as the actual web server, and manages the connections to and from the web server as needed. This enables the load balancer to manage
multiple web servers or applications as a single instance, providing a more secure and robust topology than one allowing users direct access to
individual web servers. This is a one:many (one-to-many) virtualization representation: one server is presented to the world, hiding the availability of
multiple servers behind a reverse proxy appliance. Application Server Virtualization can be applied to any (and all) types of application deployments
and architectures, from fronting application logic servers to distributing the load between multiple web server platforms, and even all the way back
in the data center to the data and storage tiers with database virtualization.
Application Virtualization
While they may sound very similar, Application Server and Application Virtualization are two completely different concepts. What we now refer to
as application virtualization we used to call “thin clients.” The technology is exactly the same, only the name has changed to make it more IT-PC
(politically correct, not personal computer). Softgrid by Microsoft is an excellent example of deploying application virtualization. Although you
may be running Microsoft Word 2007 locally on your laptop, the binaries, personal information, and running state are all stored on, managed,
and delivered by Softgrid. Your local laptop provides the CPU and RAM required to run the software, but nothing is installed locally on your own
machine. Other types of Application Virtualization include Microsoft Terminal Services and browser-based applications. All of these implementations
depend on the virtual application running locally and the management and application logic running remotely.
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VIRTUALIZATION DEFINED - EIGHT DIFFERENT WAYS
Management Virtualization
Chances are you already implement administrative virtualization throughout your IT organization, but you probably don’t refer to it by this phrase.
If you implement separate passwords for your root/administrator accounts between your mail and web servers, and your mail administrators don’t
know the password to the web server and vise versa, then you’ve deployed management virtualization in its most basic form. The paradigm can be
extended down to segmented administration roles on one platform or box, which is where segmented administration becomes “virtual.” User and
group policies in Microsoft Windows XP, 2003, and Vista are an excellent example of virtualized administration rights: Alice may be in the backup
group for the 2003 Active Directory server, but not in the admin group. She has read access to all the fi les she needs to back up, but she doesn’t
have rights to install new fi les or software. Although she is logging into the same sever that the true administrator is logs into, her user experience
differs from the administrator. Management virtualization is also a key concept in overall data center management. It’s critical that the network
administrators have full access to all the infrastructure gear, such as core routers and switches, but that they not have admin-level access to servers
Network Virtualization
Network virtualization may be the most ambiguous, specifi c defi nition of virtualization. For brevity, the scope of this discussion is relegated to
what amounts to virtual IP management and segmentation. A simple example of IP virtualization is a VLAN: a single Ethernet port may support
multiple virtual connections from multiple IP addresses and networks, but they are virtually segmented using VLAN tags. Each virtual IP connection
over this single physical port is independent and unaware of others’ existence, but the switch is aware of each unique connection and manages
each one independently. Another example is virtual routing tables: typically, a routing table and an IP network port share a 1:1 relationship, even
though that single port may host multiple virtual interfaces (such as VLANs or the “eth0:1” virtual network adapters supported by Linux). The single
routing table will contain multiple routes for each virtual connection, but they are still managed in a single table. Virtual routing tables change that
paradigm into a one:many relationship, where any single physical interface can maintain multiple routing tables, each with multiple entries. This
provides the interface with the ability to bring up (and tear down) routing services on the fl y for one network without interrupting other services
and routing tables on that same interface.