How do you do Load Testing and Capacity Planning for Web Sites
I was wondering if there is a way to actually determine how many users my VPS can handle until it will run out of Memory. I have a small VPS with 3 assigned CPU's and 4 GB RAM.
This specific machine runs on WHM/cPanel , CentOS 5 x 64 and NGINX. I host several very small (private) and one medium sized Magento store ( ~ 2500 products + Memcached enabled). This store has several thousand page-views a day.
In recent days however I have noticed that this specific store throws out an error log of exhausted RAM. I reckon this happens when too many users are on the store at the same time. Performing an upgrade to more RAM and additional CPU's would generally not a problem, but before I do that I would like to know if there is an actual way how many users or simultaneous visits my store can handle so I can choose the correct upgrade for me.
I am certainly not a pro therefore I would very much appreciate some expert advise.