What is the number of Ruby instances needed on a server?

Hi there,

what does the number of Ruby instances a server keeps running really
depend on?

Can I model/calculate that somehow as a function of the number of users
on the website or do I just have to wait and see how the situation
evolves?

I really do hope it's not 1 ruby instance per user that's necessary,
because the instances I saw on my server were all using between 120MB
and 140MB of memory, which seems huge to me (I'm a novice to all that,
though).

Thank you very much for any explanations!
Tom

I really do hope it's not 1 ruby instance per user that's necessary,
because the instances I saw on my server were all using between 120MB
and 140MB of memory, which seems huge to me (I'm a novice to all that,
though).

It's a function of how much traffic you'll be handling. If you need to
be able to handle 100 requests/s and your instances can handle 10
requests/s then you'll need about 10 instances. How that maps onto
numbers of users depends on your site.

Fred

Thanks, Fred!

1 question back - if you say...

...and your instances can handle 10
requests/s then...

...is the "10 requests/s" per instance the average capacity of a Ruby
instance? If not, do such figures exist or make any sense? Or would I
have to calculate my own instance capacity, simply based on what my
server's hardware actually swallows during usage?

You have to performance test based upon likely usage scenarios (click flows) for your app. I've never come across good metrics in any programming language for "how many users can a web app handle". It just depends too much on how the users use the app and what the app does to respond to those users.

Best Wishes,
Peter

Got it, thanks a lot guys!