[PATCH 2 of 3] Upstream: allow recovery from "429 Too Many Requests" response

[Piotr Sikora]

Hi Maxim,

> Not sure it's good idea to don't count a 429 response as a peer
> failure.  Contrary, counting it as a failure will naturally reduce
> load on the particular server, resulting in less rejects.

But 429 can be returned on a per request basis (think client IP
exceeding limit_req limits, or a logged in user that's rate-limited
based on API usage), so I'd question marking backends as failed
because of that.

Best regards,
Piotr Sikora