Heroku Cedar and nginx (gzip)
You must be accessing these apps through a domain pointing to these IPs:
75.101.163.4475.101.145.87174.129.212.2These are the apex faces and they are in front of both bamboo and cedar apps. Varnish is there for bamboo, but any request that goes through them ends up going through varnish too.
These faces are only for apex domains. If your app is under a subdomain such as www, it should be setup as a CNAME pointing to appname.herokuapp.com. When setup like that, requests will not go through varnish.
For more on Apex's and Heroku, see here: http://neilmiddleton.com/the-dangers-of-a-records-and-heroku/