nginx is not caching anything. Every request that's supposed to be cached has "http cacheable: 0" in debug log.

Test request is a static page with headers like those

< HTTP/1.1 200 OK
< Date: Tue, 17 May 2016 12:23:36 GMT
< Server: Apache/2.2.15 (CentOS)
< X-Powered-By: PHP/5.5.32
< Content-Length: 5
< Connection: close
< Content-Type: text/html; charset=UTF-8

Can you please suggest anything?