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More Efficient Virtualization Management: Templates
Virtualization Management is also known as :
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Cost of Virtualization Management,
Complexity of Virtualization Management.
OS, Middleware or VM Sprawl
Why do IT departments need server virtualization technology?
Historically, IT administrators provisioned a new server with every new application resulting in a large
number of servers with utilization rates of 10-15% or less, commonly known as server sprawl. Server
sprawl is responsible for a range of costs including:
- Infrastructure Costs Servers consume real estate space in the data center and electricity
required to power the servers and cool the data center. Power costs are increasingly becoming a major factor in modern
- Hardware Costs The server hardware and maintenance costs are the most obvious hardware
cost component. Add the network equipment costs such as routers or SAN switches that are required to connect the
servers to the rest of the infrastructure, and hardware costs become substantial.
- Software Costs Each server requires an OS and application licenses.
- Management Costs The biggest cost of server sprawl is the administration and management
costs. Each server must be provisioned, conigured, updated and monitored.
Why doesn’t hardware virtualization solve the issues associated with server sprawl?
Many IT departments have looked to hardware virtualization solutions such as VMware and Xen to
solve server sprawl. Hardware virtualization consolidates servers and helps to solve the hardware and
infrastructure costs, but it can create a new problem “OS or VM sprawl”. Any hardware virtualization
server contains an OS in each virtual machine as well as the host OS (even a ‘hypervisor” is a Linuxbased
OS). Also, virtualization makes provisioning a new OS instance so easy that administrators
deploy more detailed and customized OS environments. As a result, administrators must manage
hundreds of VM images with many copies of the operating system and IIS, ASP.NET, SQL Server and
other middleware that have to be updated independently.
To address this problem Virtuozzo uses a unique template-based approach to software provisioning
that exploits similarities between OS and applications running in different virtual environments. Using
templates, administrators can consolidate OS and application management so that only a single
instance of a software package is required and managed on a physical machine regardless of the
number of virtual environments that use the software.
Virtuozzo templates reduce the duplication of software used multiple times on a virtualized server,
making it possible to manage a single instance of software on a server. A master template is created
on the Virtuozzo server in a proprietary template area that is used as a reference for application and
OS templates loaded in virtual environments. Instead of physically copying software iles and registry
entries to each VE, Virtuozzo creates copy-on-write links to the main templates held in the Virtuozzo
File System (VZFS) template area. The template provisioned in a VE is the collection of links.
In this illustration, the VEs do not contain
copies of the actual bits of the OS and
applications; they contain templates with links
to the actual OS or application iles held on in
the VZFS Template Area. A virtual environment
requires an OS template, and may possibly
contain one or more application templates.
To keep VEs isolated and to support unique
VE coniguration requirements, if an OS or
application running in a VE writes to a ile or a
registry entry, the link is broken and changes
are made inside the corresponding VE. The
dropped link ensures that the master template
How do other virtualization technologies treat Operating Systems and applications?
All other commercial virtualization
technologies use hardware virtualization or
para-virtualization. Hardware virtualization
has a base-line OS or hypervisor (modiied
Linux kernel). Each Virtual Machine contains
a complete and unique copy of an Operating
System and any applications. In the example
to the right, the Administrator is now managing
four separate OSs and four separate
applications. The exact same coniguration
shown above deployed in Virtuozzo has a
single operating system and two applications
Virtuozzo Template Advantages
Regardless of the number of VEs that are running an application, all of the instances point to the
same ile. Therefore, the underlying OS shares memory pages between the instances just like it
shares memory pages between several instances of bash or Internet Explorer. Thanks to memory
sharing, Virtuozzo allows for 2-4 times higher density1 for typical workloads with up to 10 times higher
density for web-based applications.
- Single Instance Management A single OS is managed on any Virtuozzo server, no matter how
many virtual environments reside on the server. Templates may also be used on applications to provide the same single
instance management beneit.
- Multi-Server Management Templates are easily managed across multiple physical servers.
A template can be provisioned on multiple servers at once. Also, when a VE is migrated between servers, all required
templates are automatically copied.
- Consolidated Patching and Updating With a single OS or application instance, patches are
applied only once per physical machine, regardless of the number of VEs on the machine.
- vzcache vzcache is a system tool that scans VEs to detect and merge identical iles. Often
external patch management or update software will break links to templates and create duplicate iles in the virtual
environments, vzcache searches and recreates the links and cleans up the ile duplication to regain its original levels of
- Fast Provisioning VEs are created within seconds. No full OS or even application copies are
necessary; using the template capability the links are created very quickly.
- On-Line Provisioning and Updates Virtuozzo application templates are provisioned and
updated on-line without restarting the physical server.
- Fast Patch Roll-Back Many IT organizations like to test new patch levels before deployment.
Templates allow easy re-application or rollback to a pre-patched software state.
- Eficient Backup/Restore Virtual environments have a comparatively small footprint because
the OS and potentially applications are stored in the templates. Because of this small size, deployment, backup, restore
and migration are very fast operations.
CREATING A TEMPLATE
To simplify the template creation process, Virtuozzo ships with both command line and GUI tools1
for creating OS and application templates. On Linux, a template may be created from any stock
linux distribution package DPkg (debian) Red Hat Package Manager (RPM) application. The
template creation tool will help create a coniguration ile that enumerates top-level packages, and all
dependent packages will automatically be included. OS template creation is a bit more involved due
to the large number of packages and more complex dependencies.
On Windows, the template creation tool records all the ile and registry writes during the installation
of an application. An OS template is created when Virtuozzo is installed on Windows machine and
can be modiied later.
One of Virtuozzo’s more recent innovations is EZ Template technology. EZ Template technology
takes advantage of the online distribution
repositories that many OS vendors provide.
EZ Templates creates a host-level repository
that contains many iles that different templates
need. The EZ Template is like a recipe of
these iles, pulling the appropriate iles for
each template, even further reducing software
EZ Templates search the online repositories and
automatically take the correct updates. EZ Templates make single instance software management
easy, the master template is updated and may be distributed to the corresponding VEs. EZ
Templates is also smart enough to extract information regarding software dependencies and resolves
these dependencies automatically. Loading and updating VEs with deployed EZ Templates is simple
and easy as it has built in intelligence and lexibility to ind the best potential source iles to access
and automatically resolves software version mis-matches.
PROVISIONING AN APPLICATION USING A TEMPLATE
To provision a templated application into a virtual environment, Virtuozzo creates all required copyon-
write links back to the master template. Even for large templates, the whole process only takes
few seconds, since very little data is copied. From an administrator standpoint, provisioning an
application to a virtual environment is as simple as running a single command or a wizard.
UPDATING A TEMPLATE
SWsoft maintains a set of all supported OS and an extensive amount of application templates;
updates for these template updates may either be updated as needed from a vzup2date tool or can
be conigured to update automatically. For the automatic update, Virtuozzo periodically checks the
centralized package repository2 and downloads the latest versions of all packages for each
template. When a package is updated in a template, a new version of the template is created. Old
versions of the iles are kept, not overwritten, and VZFS links in VEs get remapped to the latest
version of the template. If there is a problem with the updated version of an application, Virtuozzo can
instantly roll-back a “bad” update by re-mapping the links to the “last known good” template.
Creating a few hundred links is much less stress on the I/O of the system than copying several
gigabytes of a complete disk image. The template-based architecture makes updates much less
intrusive than a normal OS or application update, especially large scale update roll-outs.
Templates are also provisioned and updated on-line, without any downtime or restarting the machine,
which is important for any production level application.
Virtuozzo template-based software deployment provides a number of advantages including:
- Consolidated OS and Application ManagementVirtuozzo templates dramatically lower
software management costs by making a single instance to manage on a server, and the ability to manage them easily
- Ultra Fast Operations Templating deploys comparatively small amounts of data, enabling
extremely fast provisioning, updates and migration.
- Density The code sharing capabilities provided by templates enable a much higher density
of virtual environments than other virtualization technologies.
- Dramatically lower TCO Virtuozzo provides 3-5 times lower TCO compared to hardware
virtualization technologies, with 2-3x savings on hardware alone and over 3x decrease in operating costs.
Overall, Virtuozzo provides offers an order-of-magnitude improvement in manageability and eficiency
compared to managing standalone servers and hardware virtualization technologies.
Appendix 1 – Template Architecture Terminology
The underlying technologies that make templates work are VZFS (Virtuozzo File System), VZFS links,
VZFS template area and VZFS private area.
System Metadata On Windows, templates contain all of the registry entries that the OS or application needs to run
VZFS Virtuozzo File System provides each VE with the illusion of having its own ile system. VZFS brings together iles
in the VZFS template area and iles private to the virtual environment into a single virtual ile system namespace inside
the virtual environment. VZFS is implemented as a ilter driver on top of the existing native ile system. Because of the
“ilter” approach, VZFS does not affect functionality or performance of the underlying ile system – features like journaling,
transactions, ACLs work exactly the same way.
VZFS Links Virtuozzo uses VZFS links to store the mapping back to the master template. VZFS link is a secure
copy-on-write sharing mechanism that works below the ile system layer of the host OS. VZFS links are not regular hard or
symbolic links and they are not implemented on top of existing linking mechanisms of the underlying ile system. VZFS links
are implemented completely in VZFS, which overcomes certain undesired properties of regular links. For example, to allow
proper copy-on-write sharing, VZFS links have their own access modes, unlike UNIX symlinks, which always have 0777.
Copy-on-write ensures consistency of the host OS and protects VEs from each other, while preserving compatibility with
existing applications. Whenever an application running inside VE writes to a ile that is a VZFS link to a shared ile, a private
copy of this part of the ile is created and stored inside the VE so that subsequent reads will return the modiied data. The
master template remains intact, and the changed made from within VE will only be visible in the same VE.
VZFS Template Area Virtuozzo allocates a special purpose area to store all master OS and application templates.
VZFS links point to the iles stored in this area. To facilitate template management operations, Virtuozzo keeps track of what
templates are stored inside the template area.
VE Private Area All iles and data that are speciic to a virtual environment are stored in the “private area” of a virtual
environment, which includes data created by copy-on-write operations.
vzcache vzcache is a mechanism for ighting “ile sprawl”. Patch, application management
software or application speciic auto-update capabilities may break links and ultimately create full copies of software from
previously templated applications. To mitigate this effect, the vzcache tool scans VE ile systems and searches for identical
iles. Identical iles are moved into a special VZFS cache area in the host OS, and the link is replaced.
Table of Contents
- Table of Contents
- OS, Middleware or VM Sprawl 3
- Why do IT departments need server virtualization technology?
- Why doesn’t hardware virtualization solve the issues associated with server sprawl?
- Virtuozzo Templates
- How do other virtualization technologies treat Operating Systems and applications?
- Virtuozzo Template Advantages
- Eficiency: Density
- Template Management
- Creating a Template 6
- EZ Templates
- Provisioning an Application Using a Template
- Updating a Template
- Appendix 1 – Template Architecture Terminology
- Appendix 2 – Management Console Screenshots