How Virtualization Helps Software Developers

Virtualization technologies aren't just for server consolidation. They've long been valuable tools to anyone writing or testing software.
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Virtualization's big push to fame was arguably kick-started by VMware's Workstation product, which allowed individual users to run a bunch of OSes, versions or instances (similar to multiple application windows) instead of having a one-at-a-time multi-boot environment. In many companies, virtualization arrived with developers first using the technology quietly to do testing and development, then introducing the virtualization tools to IT higher-ups.

While today, computer virtualization fuels many production environments, like servers, desktop infrastructures, and as a provisioning tool, virtualization is also used by a growing number of software developers. For starters, they use virtualization tools to provide a range of target environments for development and testing (such as different operating systems, OS versions and browsers), and also to provision or re-provision configuration instances quickly and easily. Here's a look at how and why some of today's developers are using virtualization and what their quibbles are with the technology as it stands.

Provisioning Multiple Test Environments
Mark Friedman, a senior software architect, works in Microsoft's Developer Division, where more than 3,000 people create Visual Studio and the .NET Framework. Friedman himself works mainly on the performance tools that ship with Microsoft's Visual Studio Team System. "About two-thirds of the people in my division are in development and testing — and most of these developers and testers are using system virtualization (via Microsoft's Hyper-V technology) as one of their key productivity tools," says Friedman, who is also a board director of The Computer Measurement Group.

One key advantage is virtualization's ability to set apart an unstable environment, which is something any developer expects in early phases of application design. As the Microsoft tools are developed, says Friedman, testing early versions may destabilize a developer's entire computing environment.

"That's the nature of the beast," he says. "Almost anything except the simplest desktop application can crash the system. I often tell my developers that if they aren't crashing the system regularly, they are not trying hard enough. We appreciate virtualization technologies because they save a lot of time, and let our developers spend more of their time on the challenging stuff, not the mundane and extremely time-consuming aspects of prepping
test environments."

Like other virtualization tools, Microsoft Hyper-V lets users 'snapshot' the system at a 'last known good version.'

"We create a rollback that allows us to restore the system to that previous good state within minutes," Friedman says. "The alternative is having to re-image the computer or re-build the environment, which can take hours," says Friedman. "This is a tremendous timesaver."

Friedman's group also makes extensive use of virtualization and virtual machine (VM) images in quality assurance (QA) testing. "Once you get past unit testing by the developers, we like to talk about the test matrix — what versions of the OS does it run on, for example," he says. "Then we need to test against both the 32-bit or 64-bit versions of each. Using VM images is the fastest, cheapest, most flexible way to maintain a variety of testing environments. In our QA labs, we are doing this all the time; we do a lot of automated testing, so we stockpile these images as VMs, and point our test suite at them. It's invaluable. We save so much time you wouldn't believe it."

The ability to snapshot, and restore a working image within minutes, rather than wait hours for a rebuilt system, is particularly important. "You're often looking at bugs where you have to spend a day or two to set up the environment just to reproduce a bug, so the time you spend having to rebuild again and again — that's a time waster," says Friedman. "That is loss of productivity."

For example, when a bug causes a system crash, the developer has to work backward to identify the point where the system crashed. "People often initially set breakpoints too far into the process and the system crashes again.
Since a developer can easily be crashing the system several times a day, being able to restore quickly and then re-run the debugging session while the problem is still fresh in their minds is a great benefit," Friedman says. "When you're troubleshooting a complicated bug, it's good to stay in that groove."

Virtualization is a great boon to iterative testing, developers say. "We have lots of test systems for use by our developers — each of which needs its own x86 control system. Instead of getting a lot of PCs, even the cheapest ones, we're using virtualization to create VMs which then 'attach' to the external cluster boards," says Adam Moskowitz, senior software engineer at SiCortex, which builds and sells a range of energy-efficient computers.

SiCortex's development department uses the free version of VMware Server on a somewhat-beefy rack-mounted server (equipped with 2- or 4 dual-core x86, 4 GB RAM, 300GB hard drive) which can run from four to eight control system VMs, says Moskowitz. "Because there's very little load on the control system, this works just fine, at lower capital expenditure. Over half of our roughly 25 engineers use these virtualized systems."

A primary benefit of virtualizing the control systems, says Moskowitz, is ease of testing. "Want an experimental system? Clone a standard VM and away you go," he says. The toolset is also valuable because of its ease of configuration; developers can build a VM with the latest software once, and then clone it as many times as needed.

Mike Brescia, who works for a company making real-time environmental data recording, and retrieval, says, "In addition to offering its system as a virtual appliance, our company's developers use virtualization to put up different test environments, like Windows and Linux, on fewer hardware boxes."

Cloning a clean computer system for testing purposes is much easier than copying a disk image and using Clonezilla, Brescia says. "Running a VM does not require tearing down and wiping a complete system; we only need to be careful not to overload resources on the host machine," adds Brescia.

The fifteen Web developers at design and marketing firm Eli Kirk, have to cater to a number of Web browsers and operating systems, says Connor Boyack, Eli Kirk's senior web developer, who uses Parallels version 4 on Mac OS X Leopard, and runs VMs of Windows XP, OpenSUSE 11 and Windows 7 Beta.

"Creating functional and aesthetically identical sites requires a great deal of browser testing, which makes virtualization a must," says Boyack. "Virtualization allows me to use multiple operating systems and multiple browsers collaboratively and seamlessly — when Windows XP is playing nice)."

There's a huge advantage in the ability to test a dozen different scenarios simultaneously to ensure a consistent user experience, agrees Nick Gauthier, a developer at SmartLogic Solutions. "Another advantage is being able to boot up a specific version and browser when a client has a complaint. We no longer have to say 'Well, I don't run that browser, I'm on Linux;' now we can say, 'one moment please; ah, I see the problem and I'm fixing it now.'"

"We use virtualization to test our software on the platforms and applications we support (for QA), and to replicate customer environments when there are customer issues for support," says Eric Floehr, CTO at 3X Systems, a startup that developed and sells a remote backup appliance.
"Virtualization allows us to quickly bring up and tear down environments, and allows us to do so with a minimum amount of physical hardware." The ability to test against a large number of platforms and environments with a minimum of capital outlay is especially important in a small startup company. Plus, "It greatly improves the quality and reliability of our product," adds Floehr.

Tamoggemon Software focuses on programs for handheld computers, originally for Palm OS and now also Symbian OS Series 60 and PocketPC. "I am using virtualization a lot for various reasons," says developer Tam Hanna. "My main reason is the prevalence of Cygwin or Eclipse based development systems (Eclipse for J2ME, PODS from Palm and Carbide from Nokia). Installing them all onto one machine causes all of them to break. So I need to use virtualization in order to be able to do my job.
Furthermore, I like to use VMs to keep my configuration settings the same across all my machines."

At MarkMail, a free service for searching public mailing list archives, "Our team is using virtualization in a number of ways," reports John D. Mitchell, developer at MarkMail.

"The key is that virtualizing each and every service in the system gives us a lot of flexibility. In development, we aren't stressing the physical resources much so we have lots of virtual instances running on just a few hardware nodes, including the database." MarkMail is using OpenVz so the images in the developer sandboxes are identical to the deployment environment. "Virtualization makes it very easy to test different setups, versions, etcetera — we can always just blow away an instance and re-instantiate it from a clean checkpoint," Mitchell says. Using virtualization reduces the amount of hardware they need to buy and manage, according to Mitchell. "In total, we're running about a 3:1 ratio of virtual instances to hardware nodes."

The Limits of Virtualization
There are, developers acknowledge, part of the process where virtualization can't help.

"One area where virtualization doesn't help is in stress testing our product, which is a network-based backup appliance," notes 3X's Floehr. "While we could test 10 simultaneous clients virtually, it isn't a true stress test because the 10 clients are only going through, say, four physical CPUs and two NICs, which are constraints that would not exist if they were 10 physical clients in the real world."

"Virtualization does add some complexity," adds MarkMail's Mitchell. "It always adds some latency. But, even worse, you can't rely on VMs to give a clear view of the performance characteristics as you change the underlying execution environment, such as going from development and testing into production."

Finally, Mitchell notes, "The current generation of desktop virtualizers still have too many annoying quirks, bugs and missing features," at least with regard to their use by developers for software development. "For load testing or scaling, you have to run on the raw hardware, the physical machine," says Microsoft's Mark Friedman. "Performance characteristics, unless you expect to deploy on a VM, are very different.

And the same applies to the state-of-the-art for performance measurements; you can't trust the [physical machines] you get on a VM currently."

Although, Friedman notes, over time he expects this to be fixed.

Also, says Friedman, the para-virtualization approach used by the virtualization industry can change some underlying aspects of the OS, notably the OS drivers. "So if you have a dependency on specific drivers or hardware environment that will be impacted. For example, there's a virtual NIC, and there's a specific driver. The driver is 'virtualization-aware.' You have to understand that if you need testing against a native set of drivers, you won't see that within a VM. So this impacts people doing driver development, but not web developers, etcetera."

And, Friedman points out, "If you have a multi-tiered application, which requires several machines, consolidating these to shared hardware means you get a functional but not a performance test."

Despite those quibbles, virtualization already gives developers real benefits. "Virtualization makes our developers more productive once they learn to work with the technology," says Friedman. "It allows them to spend more of their time in coding, testing and debugging. It eliminates a lot of time spent in set-up and preparation, which isn't where we want them to be spending the bulk of their time."

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BY Daniel Dern
Source：CIO.IN

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