My Rails 3.2 app uses — via #stale? — If-Modified-Since HTTP header in the request and Last-Modified header in the response to decide whether it should generate some data dynamically. This works extremely well in development (whether using webrick or unicorn_rails) as curl -D headers.txt shows that if the correct If-Modified-Since value is provided a 304 response is sent, while the Last-Modified header is otherwise sent along the request data.
Unfortunately once deployed behind nginx, neither If-Modified-Since (providing the correct header value) is passed to unicorn — and thus the Rails app — nor Last-Modified is propagated to the client: the request is unconditionally generated and the response never contains the proper headers.
