nginx does not write to cache behind Varnish

Question

I have nginx as a reverse proxy to a remote web server. Cache is written to file. However, when I place Varnish in front of it, nginx stops writing to cache file, which causes a performance hit and it doubles the traffic.

How it is possible that a front-end (Varnish) can tell nginx not to cache those requests? I tried to debug but not found anything. My nginx configuration is something like this:

server { ... location / { ... proxy_ignore_headers Set-Cookie Expires Cache-Control; proxy_cache p-cache; } } 

Again, if I make direct request to nginx, there is no problem. But I have to use Varnish which is the unique door to other service to that server.

Answer 1

I've found it. It is because of proxy_cache_min_uses = 3 that I set in another place. With this declarative, nginx won't cache to file when there are less than 3 hits on the same url.