We have a D7 site I'm trying to cache with Varnish. The assets are caching fine but for some reason every page is served with this header:
Cache-Control: no-cache, must-revalidate, post-check=0, pre-check=0
The pages are quite heavy to render and end users aren't authenticated, so I'd really like to find a solution. How can I find out if a module is preventing caching? What else could cause this? We have a similar site that plays completely nice with Varnish but I haven't been able to spot the difference yet.
Edit: I checked the site with http://www.isvarnishworking.com/ and it says Varnish is working - "sort of". That is, the age is smaller than one, meaning something is preventing the page from being cached. Below are the full response headers as reported by the service.
Server: Apache X-Drupal-Cache: MISS Expires: Sun, 19 Nov 1978 05:00:00 GMT Last-Modified: Mon, 27 Apr 2015 17:11:55 GMT Cache-Control: no-cache, must-revalidate, post-check=0, pre-check=0 ETag: "1430154715" Content-Language: en X-Generator: Drupal 7 (http://drupal.org) Content-Type: text/html; charset=utf-8 Content-Length: 45567 Accept-Ranges: bytes Date: Mon, 27 Apr 2015 17:11:56 GMT X-Varnish: 1868715414 Age: 0 Via: 1.1 varnish Connection: keep-alive X-Varnish-Cache: MISS