Re: How to prevent running out of connections?

Server NGINX
1

[Hello - I sent this last week but did not receive any responses so I am
resending it in hopes of getting some information. Thank you!]

How do I make sure we don’t run out of available connections for our
nginx 6 box?

For instance when I run stub_status I see that I have x active
connections. I can also see how the keepalive setting in nginx impacts
this number.

It seems that under heavy load where connections are coming in at a much
faster rate than the keepalive timeout is expiring, that things could
get to a point where the number of active connections becomes too great
and then there would not be enough connections available for new users.

A few questions please:

  1. Is such a situation that I described above possible?

  2. In such a situation, would nginx automatically free the idle
    keepalive connections so that it could have more connections available
    for use?

  3. What nginx and/or Linux settings (I am using Fedora core 8 if that
    matters) controls what the maximum number of connections is that my box
    can have active? How can this be bumped up?

Obviously under some heavy load a box will reach a physical maximum that
it is capable of serving. That is ok and why we have other boxes
available. However I want to understand how this works so that I can
keep an eye on the connections and say “Hey that’s getting awfully close
to our limit - time to get another box up!”. Right now I have no idea
how to predict what that limit is. Thanks!

2

Rt Ibmer,

I think you replied to my post on “Surviving Digg” a while back - there
were
some useful tips throughout that thread, if you still have it. I’d be
happy
to forward that email thread, if you’d like.

I also set worker_rlimit_nofile to a relatively high value - that seemed
to
help things out on the box.

On that note, I’m not sure what a reasonable permanent value for that
variable should be, if anyone has any insight on that? And how is that
related to worker_connections?