Forming a web application cluster with 3 VMs running in the same physical box

Are there any advantages what so ever to form a cluster if all the nodes are Virtual machines running inside the same physical host? Our small company j开发者_运维百科ust purchased a server with 16GB of Ram. I propose to just setup IIS on the box to handle outside requests, but our 'Network Engineer' argue that it will be better to create 3 VMs on the box and form a cluster with the VMs for load balancing. But since they are all in the same box, are there actual benefits for taking the VM approach rather than no VMs?

THanks.

No, as the overheads of running four operating systems would take a toll on performance, plus, I believe all modern web servers (plus IIS) are multithreaded so are optimised for performance anyway.

Maybe the Network Engineer knows something that you don't. Just ask. Use common sense to analyze the answer.

That said, running VMs always needs resources - but you might not notice. Doesn't make sense? Well, even if you attach the computer with a Gigabit link to the Internet, you still won't be able to process more data than the ISP gives you. If your uplink is 1MB/s, that's the best you can get. Any VM today is able to process that little trickle of data while being bored 99.999% of the time.

Running the servers in VMs does have other advantages, though. First of all, you can take them down individually for maintenance. If the load surges because your company is extremely successful, you can easily add more VMs on other physical boxes and move virtual servers around with a mouse click. If the main server dies, you can set up a replacement machine and migrate the VMs without having to reinstall everything.

I'd certainly question this decision myself as from a hardware perspective you obviously still have a single point of failure so there is no benefit.

From an application perspective it could be somewhat tenuously suggested that this would allow zero downtime deployments by taking VMs out of the "farm" one at a time but you won't get any additional application redundancy or performance from virtualisation in this instance. What you will get is considerably more management overhead in terms of infrastructure and deployment for little gain.

If there's a plan to deploy to a "proper" load balanced environment in the near future this might be a good starting point to ensure your application works correctly in a farm (sticky sessions etc). Although this makes your apparently live environment also a QA server, which is far from ideal.

• from a performance perspective, 3 VMs on the same hardware is slower
• from an availability perspective, 2 VMs will give higher availability (better protects from app software failures, OS failures, you can perform maintenance on one node while the other is up).