upstream retries with a single server

[Arvind Jayaprakash]

Hello,
  From the way I understand if there are 'n' servers listed as part of
an upstream block & upstream returns failure (as defined by
proxy_next_upstream), then nginx retries the same request on another
upstream server and this repeats till every upstream is tried once
(excluding those that are considered to be down).

If an upstream block is defined with exactly one active server, I see
that the request gets retried on the same upstream in case of a failure
upto 'max_retries' number of times. Logically, I'd expect it to try just
once and then give up if upstream fails to provide a suitable response.

Could someone tell me what is the expected behaviour?