503 errors on POST

[Modesto Alexandre]

Hello,

I have a problem with Varnish, from time to time I get errors 503 on the 
"POST"

Errors are infrequent, but annoying for users

I can not identify the source of the problem

My setup consists of:

* A server Varnish
* 3 going backends on the same server (3 routes)

Here are the errors I have (I have masked the private information):

http://demo.ovh.net/view/6ac24fbc5400039bc86fd3444556ef76/0.colored

Do you have any leads?

How to find the problem in production?

Thank you,
Alex.