thank you so much maxim

i have read the documentation at http://nginx.org/en/docs/http/ngx_http_proxy_module.html and am trying to understand all that. it's not easy ...

i'm serving video files (mp4 or webm). that's where these "an upstream response is buffered to a temporary file" warnings occur.

how can i find out how far i should increase the buffers until these warnings are gone? how would you do this?

second problem:
when i made changes in the css file, uploaded that, then the nginx server was still serving the older version. because of "proxy_cache_valid 200 302 304 10m;" - how can i tell nginx to refresh cache asap when a new file was uploaded?

cheers
michael