Stress testing a server and VPS's vs. Dedicated servers

Question

We used to have a dedicated server (1&1) and very infrequently ran into problems with the server having issues.

Recently, we migrated to a VPS (Wiredtree.com) with similar specs to our old dedicated server, but notice frequent problems running out of memory, mysql having to restart, etc... both when knowingly running intensive scrips and also just randomly during normal use.

Because of this, we're considering migrating to another at VPS - this time at Slicehost to see if it performs better.

My question is two fold...

Are their straightforward ways we could stress test a VPS at Slicehost to see if the same issues occur without having to actually migrate everything over?

Also, is it possible that the issues we're facing aren't just because of the provider (Wiredtree) but just the difference between a dedicated box and VPS (despite having similar specs)?

Answer 1

The best way to stress test an environment is to put it under load. If this VPS is hosting a web application, use one of the many available web server benchmark tools: ab, httperf, Siege or http_load. You don't necessarily care that much about the statistics from the tool itself, but more that it puts a predictable load on the server so that you can tune Apache to handle it, or at least not crash and burn.

The one problem you have with testing against Slicehost is that you are at the mercy of the Internet and your bandwidth to Slicehost. You may not be able to put enough load on the server to reach a meaningful conclusion.

Instead, you might find it just as valuable to run one of the many virtualization products on the market and set up a VM with comparable specs to the VPS plan you're considering. Local testing over your LAN will allow you to put a higher and more predictable load on the server.

In either case, you don't need to migrate everything, but you will need to set up an environment for your application to run in, with representative data in your database.

A VPS with similar specs to a dedicated server should perform approximately the same, but in order to get good performance, you still need to tune Apache, MySQL and any other long-lived server processes. In my experience, the out-of-the-box configuration of Apache in many Linux distributions is not ideal and will allow far too many child processes, overcommitting memory and sending the server into a swap-death spiral.