Recommended specifications for Virtualization needs

Swakoo · 08-21-2008, 05:19 AM

Hi guys,

I'm planning a web infrastructure, with a mind to make use of virtualization (Using Xen with RHEL/CentOS) so as to make better use of each processor/box and to save rack space, power etc...

I'm also thinking.. for example... 2 web servers.. but each having 2 guest instances.

So for Server1, it will have instance A and instance B
For Server2, it will have instance A and instance B

so I can do load balancer on 1A with 2A, and 1B with 2B
Theoractically, I should be
- utilizing the hardware better
- getting better performance (somewhat) at the same time right?

But bottom question is: what specs should I beef up?
I do know I need to have ample ram and storage space

Thanks!

crashmeister · 08-22-2008, 07:43 AM

Depends a lot on what are you going to run there.There's a good read about virtualization here.

Short version:
Basically anything that does a lot of disk I/O sucks in virtualised machines no matter what the specs are.

jlinkels · 08-22-2008, 07:10 PM

Are you *sure* you want to choose for virtualization? Do you have good reasons? Running 4 independent web sites in Linux does not require virtualization, even if you have different domains. Do you need your users to give full access to the complete machine, including rebooting etc?

jlinkels

Swakoo · 09-11-2008, 02:17 AM

hi guys,

thanks for the tips

I'm just thinking of fully utilising the processing and creating a pseudo redundant environment?

like having 2 web servers, with 2 instances each to mirror each other... in a way, i get more performance.. right?

so does web server (application only) consider for a high I/O job?

I know database is...

do advice

thanks!

farslayer · 09-11-2008, 08:27 AM

Then configure a HA Webserver with load balancing..

So you end up with

Load balancing
High availability
Fault tolerance - no single point of failure

http://www.howtoforge.com/high_avail...apache_cluster

Quote:

This tutorial shows how to set up a two-node Apache web server cluster that provides high-availability. In front of the Apache cluster we create a load balancer that splits up incoming requests between the two Apache nodes. Because we do not want the load balancer to become another "Single Point Of Failure", we must provide high-availability for the load balancer, too. Therefore our load balancer will in fact consist out of two load balancer nodes that monitor each other using heartbeat, and if one load balancer fails, the other takes over silently.

The advantage of using a load balancer compared to using round robin DNS is that it takes care of the load on the web server nodes and tries to direct requests to the node with less load, and it also takes care of connections/sessions. Many web applications (e.g. forum software, shopping carts, etc.) make use of sessions, and if you are in a session on Apache node 1, you would lose that session if suddenly node 2 served your requests. In addition to that, if one of the Apache nodes goes down, the load balancer realizes that and directs all incoming requests to the remaining node which would not be possible with round robin DNS.

crashmeister · 09-11-2008, 08:49 AM

You get less performance.

What virtualisation is good at is trying to utilise your hardware as good as possible.
If you take a hosting firm for example - if they would run one account per machine the box would hardly ever be fully used.So they throw depending on the hardware maybe 10 or more accounts on one machine and have it doing something instead having 10 boxes just sitting there and using space and power..