[Mongrel] Apache slows to a grinding halt... Did I screw up or is something wrong?

Carl Lerche carl.lerche at gmail.com
Sun Dec 17 01:56:53 EST 2006


So, I just got through a very stressful couple of hours. I've been
running a rails application for a few months on a dedicated server.
The application isn't really that intensive and has been serving
roughly 50k requests / day. It's been handling really well, really
fast, and all is good. The deployment configuration I am using is
apache 2.2.3 with  mod_proxy_balancer proxying to 3 mongrel processes.
It's' been really good to me so far handling the load like a champ.

Now, 2 hours ago, everything is seemingly normal when all of a sudden
the site grinds to a halt. Yet, it doesn't seem like I'm getting a
surge of traffic. I check the server and it is 90% idle. I check my
mongrel processes and they are still dishing out the site like champs.
The culprit is apache! It takes it 20 - 40 seconds to server a small
static html file. Something is wrong.

This is where me being a server admin noob sucks. After way too long I
find out that apache is maxing out the connections. Apache is
configured to handle 256 max connections with a 300 second timeout.
Keep alive is off. This has been working for months and for no
apparent reason doesn't seem to work anymore. Long story short, I
reduced the timeout setting to 15 seconds and it seems fine now. It
maxes out at roughly 90 connections now.

I pretty much only use apache as a front for mongrel, so I ask here.
Were my original settings completely dumb or is something else wrong?
Maybe something I can look at with how I configured apache to proxy to
mongrel? Why are so many connections staying open?

I'm no amazing system administrator, so I'm hoping that it's something
I did wrong and stupid and having a 300 second timeout is just a
mistake I made.

Any insight?

EPA Rating: 3000 Lines of Code / Gallon (of coffee)

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