Nginx $upstream_cache_status not available when used in rate limiting

[linnading]

Hi Francis,

It is "to the same upstream server"  that I care about.  I would like to
limit the request rate to the same upstream server.

The Scenarios is like:
10 requests at the same time to the same upstream server, the upstream
server should only receive requests at rate 1r/m. Last few requests will be
delayed or rejected. But for these last few requests, some of them can be
served by cache, they should not be delayed/rejected. 

Thanks,
Linna

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,268345,268386#msg-268386