FEATURE VIRTUALISATION
Testing in the Virtual Environment Try, Try Again By Daryl Cornelius, Director Enterprise, EMEA Spirent Communications
At its heart, it’s not a new idea, because it harks back to the old days of a central mainframe doing all the processing while users interact via a network of dumb terminals. It re-emerged in the early 90s with talk of the ‘thin client’. Then with internet intoxication came the idea of Software as a Service – buying usage only as needed from a source that managed all the licencing and upgrading and kept the applications in peak condition. The main difference is that a new
As you sit at your PC cursing the little window saying your software needs updating (and asking whether you would rather waste time doing it now, or waste time later) the idea of software delivered to your computer from a pure source, like mains water or electricity, becomes highly attractive. But it won’t happen just like that.
name was needed to mark the fact that this idea now works. Pioneering attempts failed simply because broadband access was not yet widely good enough to support the service, but with today’s widespread broadband it is becoming a practical proposition. It’s called Cloud Computing because instead of the processing happening inside your computer, or in the company mainframe, it happens at some unknown location in the internet cloud. It doesn’t even need to happen in any one location or piece of hardware, since it could be running on some geographically dispersed virtual machine. That’s true cloud computing, arriving
like a paid public service from who knows where. However, you could
also use the term to describe software delivery within an organisation’s intranet from a physical or virtual data centre– the so-called ‘private cloud’. As before, the key to successful service is that the network to the mobile or desktop computer must be fast enough not to frustrate a user who is used to the speed and responsiveness of on-board software. Also, in the case of software running in a virtual server, the network connecting its parts must be sufficiently fast and low-latency to allow the application to perform as well as it would on a single physical machine.
The performance challenge
Performance really is the challenge. Cloud computing potentially offers all the benefits of a centralised service – pay for what you actually use, professional maintenance of all software, single contact and contract for any number of applications, processing on state-of-the-art hardware – but it has to match the speed, responsiveness and quality experience of local software if the service is going to be accepted by the user. So how does the provider ensure that
level of service? The answer, as we shall see, must lie in exhaustive testing. The
complexity of virtual systems makes for unpredictable behaviour, you can only be sure when you have put it to the test. But there is also a fundamental problem in testing any virtual system, in that it is not tied to specific hardware. The processing for a virtual switch or virtual server is likely to be allocated dynamically to make optimal use of available resources. Test it now, and it may pass every test, but test it again and the same virtual device may be running in a different server and there could be a different response to unexpected stress conditions. Whether the central processing runs
on a physical, virtual or cloud server, it needs to hold a large amount of application software to satisfy the client base, and that software needs to be maintained with every version upgrade and bug fix as soon as they become available. It’s a complex task, and it is increasingly automated to keep pace with development. There must be a central library keeping the latest versions and patches for each application package, and some mechanism for deploying these across the servers without disrupting service delivery. At this stage the service provider is in
the hands of the application developer – the service to the end user can only
“In a virtual system, and even more so in the cloud, there can be unusual surges of traffic which lead to unexpected consequences. ” 34 NETCOMMS Volume I, Issue 4 2011
www.netcommseurope.com
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