knowing when to go to multiple mongrel instances or dedicated server

I have a rails app with a growing user base. Right now it is on a
single mongrel instance on a shared server. Is there a quantifiable
method I can use to measure when I need to add mongrel instances, or
move to a dedicated server? Are there rules of thumb for how many
users or page hits an instance can support? Or is it solely
subjective, based on when the app starts to "feel" slow?

I have a rails app with a growing user base. Right now it is on a
single mongrel instance on a shared server. Is there a quantifiable
method I can use to measure when I need to add mongrel instances, or
move to a dedicated server? Are there rules of thumb for how many
users or page hits an instance can support? Or is it solely
subjective, based on when the app starts to "feel" slow?

A couple of years old, but it's from the horses mouth...

http://rubyforge.org/pipermail/mongrel-users/2006-May/000200.html

Thanks, good info. That is more for a dedicated server, though. If
I'm on a shared server, how can I measure/compare to determine whether
I need the expense of a dedicated server?

Ed wrote:

I have a rails app with a growing user base. Right now it is on a
single mongrel instance on a shared server. Is there a quantifiable
method I can use to measure when I need to add mongrel instances, or
move to a dedicated server? Are there rules of thumb for how many
users or page hits an instance can support? Or is it solely
subjective, based on when the app starts to "feel" slow?

Ed, why not to move to phusion passenger? It's fast and intended for heavier load than mongrel (even in cluster)

tom

I'll take a look at that, thanks. My hosting provider says that
passenger is slower than mongrel in a shared environment, because of
the delay when processes have to be restarted.

But ultimately I will have the same question: how can I measure when
traffic is too much for my shared host?

Ed,

If you're hosting provider is suggesting that passenger is slower,
it's in *their* environment. You might consider another provider then.

You might take a look at the survey results we just posted at
http://rails-hosting.com.

Cheers,
Robby

I'll take a look at that, thanks. My hosting provider says that
passenger is slower than mongrel in a shared environment, because of
the delay when processes have to be restarted.

This is only relevant if you don't get enough traffic to keep the
passenger/rails instance alive. What I've read says that once up and
running passenger is faster than mongrel, but best to do your own
research.

Start here: http://www.modrails.com/documentation.html (part way down)

But ultimately I will have the same question: how can I measure when
traffic is too much for my shared host?

That's a question for them. Find out what their limits are and then
figure out when you'll hit them.

I’ll take a look at that, thanks. My hosting provider says that

passenger is slower than mongrel in a shared environment, because of

the delay when processes have to be restarted.

But ultimately I will have the same question: how can I measure when

traffic is too much for my shared host?

It seems to be a rather naive answer but can you not tell that the
traffic is too much by the fact that it slows down unacceptably? Or am
I missunderstanding the question, are you trying to predict in advance
at what traffic level it will slow down too much?