ruby - How to preserve request url with nginx proxy_pass -

i trying use thin app server , had 1 issue.

when nginx proxies request thin (or unicorn) using proxy_pass http://my_app_upstream; application receives modified url sent nginx (http://my_app_upstream).

what want pass original url , original request client no modification app relies heavily on it.

the nginx' doc says:

if necessary transmit uri in unprocessed form directive proxy_pass should used without uri part.

but don't understand how configure related sample using uri:

location  /some/path/ {   proxy_pass   http://127.0.0.1; } 

so please me figuring out how preserve original request url client?

i think proxy_set_header directive help:

location / {     proxy_pass http://my_app_upstream;     proxy_set_header host $host;     # ... }