Hosting one app on 2 virtual machines that are located on a single machine-- any problem?

Question

I have a web application, it's hosted across two different virtual machines, and it happens that the two virtual machines are located on a single machine.

All of the three physical machine, virtual machines are Windows XP.

The reason I design my architecture in this way is because I want to make my web app scalable and deployable across different machines, so I built it as such from the beginning. Now I am hosting it on virtual machine because I don't see scaling need now. However when time arises I will really deploy the web app on two different real machines for load balancing purpose.

The question: Will there be any problem if I use virtual machines to use one single web app? Is there a possibility that the virtual machines can't work as well as the real machines?

What do you think?

I am using Sun Virtualbox 2.2 in this regard.

Answer 1

As long as you're using a virtualisation technology that does sufficiently good networking to let everything talk together, it should work. There will be inevitable performance degradation, from the overhead of running the virtualisation, but for a lightly loaded website in testing, that shouldn't be a killer.

Answer 2

That shouldn't be a problem to run them all on the same physical hardware. The only risk would be that of a single hardware failure taking everything down.

As a practical example, I run a 7 server web-farm entirely virtualized, and occasionally all on the same host machine (more often split between 2 for redundancy). We use VMWare Infrastructure.

One benefit of virtualization is that as our traffic increases, we can simply allocate more cpu/network resources to the existing server farm as needed (without adding more servers). Until that point however, the resources are available for other uses.