How to determine cpu, ram needed for rails app?

Question

What is the most accurate way to determine the amount of cpu speed and ram needed to run my rails app?

I believe there are stress testing tools like Tsung, but how do I determine, for example, that I need X more ram, or X more CPU? I would like to find some way to roughly gauge the performance needs of my application so I can anticipate future needs. I think this data will also be useful for me to decide whether to upgrade one machine, or get another dedicated machine and put all the databases on that one.

Essentially, I am concerned about scaling issues, and how to anticipate them. Thanks in advance for the help!

Answer 1

I would highly recommend checking out both Heroku and Engine Yard's cloud-based offerings. There's no definitive way to tell exactly what your app will need because it really depends on how many requests are going to hit it, how long requests take (how well you've optimized it), whether or not there are background jobs, etc.

With both of these providers, you can scale as needed and you never have to think about the hardware.

Answer 2

Do you have command line access to the machines you are running your application on? A simple way to get this info is to use top, assuming it's a *NIX based machine.

top is not as sophisticated as dedicated monitoring tools but will allow you to view current CPU%, memory use etc.