FEATURE VIRTUALISATION
be as good as the latest version on the server. We hope the aplication developer has done a good job and produced a reliable, bug-free product, but the service provider’s reputation hangs on that hope until the software has been thoroughly tested on the provider’s own system. In the case of a physical server, we
do not expect any problem because the application is likely to have been developed and pre-tested on a similar server. But virtualisation and cloud computing adds many layers of complexity to the process. The speed of the storage network becomes a significant factor if the application makes multiple data requests per second, and that is just one of many traffic issues in a virtual server. Faced with such complexity, predicting performance becomes increasingly difficult and the only answer is to test it thoroughly under realistic conditions. You cannot expect your clients to play the role of guinea pigs, so usage needs to be simulated on the network. It is critical to gauge the total impact of software additions, moves and changes as well as network or data centre changes. Every change must be tested to avoid mission critical business applications from grinding to a halt. There are two aspects to testing
applications in a virtual environment. Firstly, functional testing, to make sure the installed application works and delivers the service it was designed to provide, and then volume testing under load. The first relates closely to the design of the virtual system – although it is more complex, the virtual server is designed to model a hardware server and any failures in the design should become apparent early on. Later functional testing of new deployments is just a wise precaution in that case. Load testing is an altogether different
matter, because it concerns the impact of unpredictable traffic conditions on a known system. To give a crude analogy: one could clear the streets of London of all traffic, pedestrians, traffic controls and road works then invite Michael Schumacher to race from the City of London to Heathrow airport in less than 30 minutes. But put back the everyday traffic, speed restrictions,
36 NETCOMMS Volume I, Issue 4 2011
traffic lights and road works and not only will the journey take much longer, it will also become highly unpredictable – one day it might take less than an hour, another day over two hours to make the same journey. In a virtual system, and even
more so in the cloud, there can be unusual surges of traffic which lead to unexpected consequences. Applications that perform faultlessly for ten or a hundred users may not work so well for ten or a hundred thousand users – quite apart from other outside factors and attacks that can heavily impact internet performance. So the service provider cannot offer any realistic service level agreement to the clients without testing each application under volume loading and simulated realistic traffic conditions.
The test solution
Network performance and reliability have always mattered, but virtualisation makes these factors critical. Rigorous testing is needed at every stage in deploying a virtual system. During the design and implementation phases it is needed to inform buying decisions, and to ensure compliance. Then, during operation it is equally important to monitor for performance degradation and anticipate bottlenecks, as well as ensuring that applications still work under load as suggested above. But large data centres and cloud
computing pose particular problems because of their sheer scale. Testing solutions need to be scalable, and need to test application performance holistically under realistic loads and stress conditions. The acceptability of cloud
computing depends upon delivering a quality of experience as good as local processing but without all the overheads of licencing and software version management. Quality of experience is a subtle blend of many factors such as latency, jitter and packet loss. Testing systems should monitor these under wide-ranging traffic loads, both running pre-programmed tests automatically and allowing operator intervention via a simple user interface.
The question of security
As well as delivering good quality of user experience, the cloud computing provider needs to satisfy the clients’ fears about security in the ‘cloud’. The hacker that accesses a soft switch can re-route traffic at will, and so virtualisation leads to potentially severe vulnerability across the whole business – and the social infrastructure in the case of cloud computing. Again, the growth in virtualisation demands a corresponding increase in prior and routine testing. Here it is not only the need to
test under unusual load conditions – because those are the times when attacks are most likely to succeed – but also there is a need to simulate a whole range of attack scenarios. The application must still work when tested in the context of the network security devices working under attacks and vulnerabilities, that’s real life. Test solutions now exist which deliver
comprehensive, accurate user emulation of end user traffic and unexpected attack traffic even while at high load. These can model the user behavior while scaling to full internet levels. This ‘no compromise’ approach is important since measuring the impact to the user and the network while loading the application with real-world loading patterns helps identify, isolate and resolve problems before the provider commits them to service agreements and puts them on-line. Cloud computing offers many
advantages to the user, but the provider must assure the client that the service will consistently deliver on its promises. Fail, and users will vote with their feet. The only way to ensure success is to offer a tried and tested service.
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