[a little OT] mod_proxy 502 errors in dual apache setup

Hi folks,

Slightly OT but hopefully someone on here has had similar experience.
I've got a site with fairly heavy traffic and a light/heavy apache
setup. Occasionally the back-end servers seem to get swamped and
suddenly every request from the front end starts getting a 502 proxy
timeout until I restart both apache servers.

I'm about to start digging through logs to try and track down the issue
but wondered if anyone who's seen this before could give me a head start.

cheers
John

Re: [a little OT] mod_proxy 502 errors in dual apache setup

502's show up when you have more connections from the front end to the
back end that it can service. The proxy server has a timeout [1], and
if it doesn't get a response within that time frame you get a 502.

You can create a custom error document on your front end for 502's to
make them a little less jarring.

[1] http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#proxytim eout

Quoting John ORourke :

> Hi folks,
>
> Slightly OT but hopefully someone on here has had similar experience.
> I've got a site with fairly heavy traffic and a light/heavy apache
> setup. Occasionally the back-end servers seem to get swamped and
> suddenly every request from the front end starts getting a 502 proxy
> timeout until I restart both apache servers.
>
> I'm about to start digging through logs to try and track down the issue
> but wondered if anyone who's seen this before could give me a head
> start.
>
> cheers
> John

Re: [a little OT] mod_proxy 502 errors in dual apache setup

On Wed, Mar 5, 2008 at 10:37 AM, wrote:
> 502's show up when you have more connections from the front end to the
> back end that it can service.

Just to expand on that a little, you should start by checking for
simple things like whether your machine was going into swap or getting
hung up on a particular database query. If you're running the maximum
mod_perl processes you can fit without going into swap, you either
need to extend the timeout and let people wait or add more hardware.

- Perrin