Problem request_timeout not working with proxy_next_upstream on proxy_connect_timeout but proxy_read_timeout (3 replies)

Hello
In our setup we have an NGNX as front-end and several back-end.
The problem is our load profile, we have a lot of simple and fast http requests, and very few but very heavy in terms of time and BE cpu requests.

So my idea is to use proxy_next_upstream for simple request as usual and it works perfectly.
And for heavy requests based on URL I want to passthrough it to BE with lowest CPU load by specifying small proxy_connect_timeout and using proxy_next_upstream timeout.
But in case of all system overload with heavy requests i don't want them to travel through all BEs because of proxy_read_timeout is about 1 minute.
I was hoping to set a request_timeout to the same value as proxy_read_timeout and from my point of view this should prevent heavy requests to travel all upstreams based on proxy_read_timeout, but they do.

I ve found a similar topic but the proposition was to make two new options to proxy_next_upstream such as timeout_tcp timeout_http or something similar.

Thanks for your future advices and comments.