Virtualization in Software Engineering

Dennis Kalinowski4/30/2007

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What is Virtualization?

Abstraction of computer resources

Servers, operating systems, applications, or storage devices

Technique for hiding characteristics from other systems, applications, or users

Used to provide different interfaces or resources

Can be used to make a physical resource appear as multiple logical resources

Or multiple physical resources appear as a single logical resource

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Why Use Virtualization?

Improve portability, security, performance, reliability

Can be used in design, implementation, testing, or deployment of systems

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Old Idea, Innovative Uses

Early 1970s, IBM 370 mainframe used virtualization to run multiple operating systems

Each operating system operated as if it had exclusive control of the hardware

Some hardware implement virtualization

Intel's Hyper-Threading Technology

Single physical processor appears as multiple logical processors

Automatic parallelization

Two or more physical processors exposed as a single logical processor

Executes multiple instructions from the current thread

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Hardware Virtualization

Virtual Machine Monitor (VMM) – aka hypervisor

Allocates system resources for each virtualized operating system or program

Layer between software and other resources (such as hardware)

Either sits directly on hardware or runs within an operating system

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Hardware Virtualization

When run within an operating system...

Host OS controls hardware

Guest OS runs in the virtualized environment

Three types:

emulation/simulation – simulates complete hardware. (Can host an unmodified OS for the same or different CPU)

native virtualization – simulates enough hardware so the guest is in isolation. (Only allows unmodified OS for the same CPU)

paravirtualization – provides an API which must be used by the guest OS.

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Hardware Virtualization

Guest OS can be altered or observed during execution

States of system can be snapshotted

Other examples of hardware virtualization

Storage devices

File systems

Accessing disk images as if they were an actual drive

Virtual memory

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Example 1 Usage of a VMM

Image from: [16] Intel virtualization technology.

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Advantages of HV

Portability

Software would not need to be rewritten for new hardware, only the virtualization layer needs to be altered

Security

Isolated environment to restrict spread of intrusion

Guest OS can be monitored to observe for calls or behavior that may indicate intrusion

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Advantages of HV

Performance

IBM 370 mainframe ran OS's that did not support threading in parallel with OS's that did

Therefore, less CPU cycles were wasted

Virtualization may be used to maximize utilization of resources

Possible issue: overhead

Loading a previous snapshot may be faster than a fresh load

Reliability

Recovery – On failure or lose, an image of system's pristine or last good state can be reloaded

Redundancy – Identical resources or software run in parallel

Hardware example: fault tolerant CPU

Software example: share load two identical servers

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Example 2 Performance

Image from: [15] Performance Evaluation on Server Consolidation Using Virtual Machines.

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Example 3 Reliability

Image from: [9] High performance fault tolerant computer and its fault recovery.

Virtualization hides the true underlying system from the running program

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Example 3 Reliability

Image from: [9] High performance fault tolerant computer and its fault recovery.

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Use in Software Development

Virtualize hardware and/or software environments

Increase portability of software by testing in various operating systems, architectures, or configuration

By isolating build/testing environments to virtual systems, you do not risk contaminating your own development system

Keep testing environments consistent or configured with minimal software dependencies

Cheaper to run multiple virtual machines than multiple physical computers

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Use in Software Development

Testing

Can observe or alter software running in virtual environment

So, ideal for debugging OS kernels

States can be snapshotted to allow exact replication of bugs or tests

After executing tests, can revert to initial state

Use with automated test suites to ensure consistent environments

Test upgrade processes

Keep a snapshot of installations for all versions or varying dependencies

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Example 4 Test Environment

Image from: [11] Test Optimization Using Software virtualization.

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Other Virtualization Technologies

Operating System Virtualization

A layer in the operating system to run servers in a virtualized environment

Each environment is a “container”

The container can restrict resources (processor usage, file systems, etc.)

However, there is no isolation from the kernel

If kernel has vulnerabilities, entire system can be affected

Protecting specific resources and other processes may be all the security required for some applications

Useful for running multiple instances of a server using different configurations

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Other Virtualization Technologies

Application Virtualization

“breaking the age old bond between physical hardware, operating system, and the program which runs on top of them”

High-Level Languages (HLL)

Java

Microsoft's Common Language Infrastructure (CLI)

Intermediate code generated by compilers get translated into native machine code using “just in time” technology

Application only compiled once for all architectures present and future

Only new HLL Virtual Machines are needed for new architectures

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Other Virtualization Technologies

Process Virtualization

“Ghost processes” - An experiment by researchers using Linux kernel

Duplicate processes

Migrate processes

Create process checkpoints

Revert to process checkpoints

Useful for testing and debugging

Saving and restoring processes to allow reproduction of process states

Or use to restore process to a good state on failures

Loading from a snapshot may be quicker than a fresh load

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Conclusion

Abstraction to simplify use of computer resources

Represent resources in simpler or different forms

Add additional functionality or ability to resources

Improve portability, security, performance, and reliability

Cheaper alternative to multiple computers

Excellent tool for testing

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References

[1] Virtualization. Retrieved April 2, 2007, from Wikipedia. Web site: http://en.wikipedia.org/wiki/Virtualization

[2] Figueiredo, R.; Dinda, P.A.; Fortes, J. (2005, May). Guest Editors' Introduction: Resource Virtualization Renaissance. Computer. 38(5), 28-31.

[3] Hyper-threading. Retrieved April 2, 2007, from Wikipedia. Web site: http://en.wikipedia.org/wiki/Hyperthreading

[4] Automatic parallelization. Retrieved April 2, 2007, from Wikipedia. Web site: http://en.wikipedia.org/wiki/Automatic_parallelization

[5] Vaughan-Nichols, S.J. (2006, Nov.). New Approach to Virtualization Is a Lightweight. Computer. 39(11), 12-14.

[6] Smith, J.E.; Ravi Nair. (2005, May). The architecture of virtual machines. Computer . 38(5), 32-38.

[7] Litty, Lionel. (2005). Hypervisor-based Intrusion Detection. Unpublished master's thesis. University of Toronto.

[8] Ligneris, B. (2005, May). Virtualization of Linux based computers: the Linux-VServer project. High Performance Computing Systems and Applications, 2005. Proceedings. 19th International Symposium . 340-346.

[9] Nakamikawa, T.; Morita, Y.; Yamaguchi, S.; Ishikawa, S.; Miyazaki, Y. (1997, Dec.). High performance fault tolerant computer and its fault recovery. Fault-Tolerant Systems, 1997. Proceedings. Pacific Rim International Symposium . 2-6.

[10] Hypervisor. Retrieved April 2, 2007, from Wikipedia. Web site: http://en.wikipedia.org/wiki/Hypervisor

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References

[11] Seetharaman, S.; Krishna Murthy, B.V.S. (2006, Sept.-Oct.). Test Optimization Using Software virtualization. IEEE Software. 23(5), 66-69.

[12] Operating system-level virtualization. Retrieved April 2, 2007, from Wikipedia. Web site: http://en.wikipedia.org/wiki/Operating_system-level_virtualization

[13] Vallee, G.; Lottiaux, R.; Margery, D.; Morin, C. (2005, July). Ghost Process: a Sound Basis to Implement Process Duplication, Migration and Checkpoint/Restart in Linux Clusters. Parallel and Distributed Computing, 2005. ISPDC 2005. The 4th International Symposium on 04-06 July 2005. 97-104.

[14] Application Virtualization. Retrieved April 2, 2007, from Wikipedia. Web site: http://en.wikipedia.org/wiki/Application_Virtualization

[15] Hidenori Umeno; Parayno, M.L.C.; Koudai Teramoto; Masato Kawano; Hiraku Inamasu; Shuuhei Enoki; Masato Kiyama; Tomoo Aoyama; Takafumi Fukunaga. (2006, Oct). Performance Evaluation on Server Consolidation Using Virtual Machines. SICE-ICASE, 2006. International Joint Conference. October 2005. 2730-2734.

[16] Uhlig, R.; Neiger, G.; Rodgers, D.; Santoni, A.L.; Martins, F.C.M.; Anderson, A.V.; Bennett, S.M.; Kagi, A.; Leung, F.H.; Smith, L. (2005, May). Intel virtualization technology. Computer. 38(5), 48-56.