Virtualization and why it is good for programmers

Question

Why does it help to know about virtualization from a programmer's perspective? Except testing and developing on several different platforms without the need of switching between operating systems is there a particular reason why virtualization is important for a programmer? Are there any details that must be kept in mind before developing on virtual instances?

Answer 1

Good for developing, because you have same server configuration in virtual machine like on production server.

http://stackoverflow.com/questions/905926/developer-software-setup

Answer 2

From a user space application there should be no difference developing for a virtualised OS versus a normal OS. There may be some gotchas if your code makes explicit assumptions of the machines memory size and number of processors and believes what the hypervisor tells you.

Answer 3

One of the main advantages is having your entire development environment as a single image file. I have a perfectly configured version of Windows Server, Visual Studio, ReSharper, etc. I can easily try a new version of something on a copy of this virtual machine without worrying about it causing problems.

I can also back up my entire dev environment to transfer it to another physical machine very easily. I've been through 3 machines in this office alone so that was a lifesaver in itself.

The only real trade-off I see is performance. You generally have to use less physical CPU cores than you actually have and less memory. With a sufficiently powerful machine this is not much of a problem though.

Edit: As nader said, I/O is obviously important for most projects as well. Although developing on a virtual machine does mean a fairly large I/O penalty compared with a native OS install, in practice I rarely find it to be a problem. The superior random access capabilities of SSDs are helping to mitigate this drawback as well.

Answer 4

If you develop a driver or something very close to the hardware with a high risk to crash the machine, you will be glad to be working on a virtual machine.

Reverting to an old state is easier than to repair a damaged OS.

Answer 5

I use it for testing our installer, because it is important to check whether the application will work on a clean installation of the operating system.

I used to do these tests by keeping a hard drive with a fresh operating system installation and making a copy of that disk for (almost) every new test run. This was very time consuming, and the virtual machine solution has saved me a lot of time. Note that this even allows you to do remote debugging as easily as when using two non-virtual machines.

Note: If you're interested, I'm using VirtualBox, which is a very good and free virtualization tool.

Answer 6

If you are developing in a virtual environment you will want to make sure you know what specifications were used to create the environment. If you have say a 4 Gig machine and create a virtual environment with 1 Gig you will want to make sure things in your development do not grow to a point that it overruns the memory. This will cause slight performance problems. I personally ran into this and it was a pretty tricky thing to track down. The scenario was that I was fixing a bug and testing it in a virtual environment. I did not setup the virtual environment by the way... The application took a performance hit because of all of the memory swapping that was taking place.

A very good use for a virtual environment is when you are developing applications that mess with the Windows Gina. It's much easier to reinstall a virtual environment than an entire PC....(been here done that too).

Answer 7

I'm surprised no one has mentioned the ease of deployment. All you need to do is get the build down on the virtual O/S and then you can copy the image to as many new servers (running some kind of virtualization solution [like VMWare]) as you want, easily scaling your application.

Answer 8

I do all of my development on a virtual XP instance under VMWare Fusion so that I can use a Mac for everything and still write .NET code ;-)

Answer 9

We have a large number of different versions / customer customisations of our software, and its not possible for 2 installs of our software to coexist on the same machine. Virtualisation allows us to replace the 50-60 physical machines that we need to maintain for testing and problem reproduction with 2-3 virtual servers - it takes around 10 miniutes to make a copy of a VHD template we have and create a new virtual machine, and as long as you allocate 1-2Gb of RAM the performance is comparable to that of a (slow) physical machine.

Virtual machines are also great for build machines.

Personally I do all of my development on my deskop machine for best performance, and remote debug into VMs. I dont run virtual machines on my desktop as it uses up too much RAM, we have dedicated virtual servers for that.

Answer 10

Being able to completely reset the state of the system is very useful to debug applications which modify their environment - If the actions are repeated after a reset, and they're constrained to the sandbox environment of the VM, you are pretty much guaranteed to get the same result.

Answer 11

• Record the state of a bug in a program, and send it to the developer (along with the entire "machine").
• Testing your code on various O.S, some of which you don't have.
• Working in a more protected environment, making sure that the code doesn't harm your system -useful for understanding dangerous programs, like viruses, and developing security against it, for writing potentially wrong hard-drive programs, and anything that can have catastrophic effects on your system.
• Easily Write your own O.S without the need to write on 'real' boot sectors, a potentially harmful act (Hope this is not new...).
• Quickly use tools and programs not found on your own O.S.
• Demonstrate a program at various times, by restoring a virtual machine, quicker and less prone to failure, than trying to recreate the state at the minutes before the demo.
• Less directly connected to programing, but surfing vie a virtual machine (for example to see documentation) has the added value that your own important system (and code) is less likely to be harmed by malicious programs.

Answer 12

From my experience in most cases the answer is typically "no" (When testing and targeting multiple platforms is removed) Both are huge reasons to be familiar with "desktop" VM solutions. Others have done an excellent job of listing rare exceptions like debugging kernel codes.

There are some quirks one must be aware of when running on a virtual machine. This is hardly an exhaustive list:

1. Loss of precsision or even time reversal in high resolution timers due to emulation of hardware resources (depends somewhat on the vm platform and operating system)

2. Virtual network interfaces ususally bridged. We've seen some extremely odd behavior in the host system with an application that sets up its own bridge between virtual interfaces -behavior which logically should not effect the host in one of the leading VM solutions.

3. Usage models - If your product has orwellian licensing codes or records state dependant behavior when interacting with remote systems you should account for what would happen if a system were "paused" and "restarted" or restarted from an earlier "state". Normally this kind of thing would be taken into account anyway in a robust implementation.

Answer 13

Sometimes they are necessary, because the platform you are programming doesn't support the standard developer environment. One such example is Sharepoint. As of Sharepoint 2007 you still need a server OS to install Sharepoint 2007, WSS, and the Visual Studio Sharepoint Extensions (VseWSS).

Thus for Sharepoint I have to use a Window Server VM to do my development work. As for Sharepoint 2010 they are supporting installations on Vista and 7 x64, but I will still use a VM, because I don't want to have Sharepoint on my main machine slowing everything down. Rather I want it in a VM where the services are on when needed and off when I don't without having to manually turn off/on each service. This in addition to the many great answers posted above.