Nginx health checks

[Barry Abrahamson]

On Jun 10, 2008, at 1:36 PM, Corey Donohoe wrote:

> On Tue, Jun 10, 2008 at 10:21 AM, Barry Abrahamson <barry at automattic.com 
> > wrote:
>> Howdy,
>>
>> First let me say how happy we are with Nginx :)  Yesterday was a  
>> pretty big
>> traffic day for us, about 36 million dynamic pageviews peaking at  
>> about 15k
>> requests/sec.  Couldn't have done it without Nginx.
>>
>> http://wordpress.com/stats/traffic/
>>
>> We have about 350 web servers behind Nginx so it is a semi-regular
>> occurrence that one of them fails for some reason (usually  
>> hardware).  Pound
>> has a dedicated health check thread, that would perform the health  
>> checks
>> and then mark servers up/down as appropriate.
>
>> Nginx, however, seems to use
>> the response (or lack thereof) from the user-initiated request as  
>> the health
>> check.
>
> Can you elaborate on what you mean here?  Things aren't getting marked
> as down from pound until a user makes a request?

We are using the reverse proxy functionality of nginx, not the web  
server functionality.  We switched from pound to nginx:

http://barry.wordpress.com/2008/04/28/load-balancer-update/

> It seems like this should be tuned at the pound level.

Pound is no longer part of the equation.

> You should
> definitely have sane thresholds for timeouts, but it sounds like your
> load balancer software is letting you down here.

Nginx is our load balancer in this case.

--
Barry Abrahamson | Systems Wrangler | Automattic
Blog: http://barry.wordpress.com