varnish default retries on backend timeout?

[Traian Bratucu]

Hello,

We have been using Varnish for a while and encountered a specific problem I don't seem to be able to figure out. Apparently on a POST request to the backend, for which the backend times out, the request is automatically retried by varnish a second time.
Obviously that is a big problem since POST data gets submitted twice. I do not have any restart statements in the VCL so I guess this is some default Varnish behavior, hopefully controlled by some global parameter.

Here is what I get logged:

-------------
   32 Backend      c 5 xxx_authenticated black_instance_1
   32 FetchError   c http first read error: -1 11 (Resource temporarily unavailable)
   32 Backend      c 87 xxx_authenticated gray_instance_2
   32 FetchError   c http first read error: -1 11 (Resource temporarily unavailable)
   32 VCL_call     c error deliver
   32 VCL_call     c deliver deliver
   32 TxProtocol   c HTTP/1.1
   32 TxStatus     c 503
-------------

Is there a way to avoid this double post?

Thank you,
Traian
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