503 errors that are not backend timeouts? ( Wordpress )

[Daniel Carrillo]

2012/7/27 Kervin L. Pierre <kervin at adevsoft.com>:
> I have a Wordpress install that gets occasional 503 errors on HTTP POST urls.  And I need to find out what's causing these.  Any help in tracking those down would be appreciated.
>
> Looking at my logs I can see that the 503 errors are not timeouts.  I've got the backend timeouts set to 5 minutes and Varnish log shows the 503 errors being sent between 5 to 40 seconds into the script run.
>
> Can anyone tell me why Varnish would return a 503 error to the client besides after a backend timeout? ( HTTP GETs are not affected )

It sounds like this ticket:

https://www.varnish-cache.org/trac/ticket/849

The workaround is "piping" POST request, and wait an implementation
which buffers the request-body.

Hope this helps.