Thanks for pointing out redbot.org, its very handy. I used it against my own heroku site prawn.heroku.com (examples of how to generate pdfs in rails with the Prawn, prawn-to libraries), and I noticed that the server times would vary as I refreshed the page.
http://redbot.org/?uri=http://prawn.heroku.com the first time I hit it, the server time was considered to be correct, but subsequent refreshes returned anywhere from 5mins ahead to 6hrs ahead. I assume this is just at the nginx server, and doesn't mean that the server time on my rails server is out of sync. Am I reading this right? thanks, -John > Hi Thomas, > > Thanks for the detailed example. It looks like Varnish is assuming a > default max-age of ~500 seconds since the Cache-Control header is set > to public but no explicit max-age is specified and the must-revalidate > directive isn't provided. redbot.org is an invaluable resource in > debugging these types of issues: > > http://redbot.org/?uri=http%3A%2F%2Ftest-caching.heroku.com%2F > > Most HTTP caches support "heuristic expiration" (details here: > http://tools.ietf.org/html/rfc2616#page-80). The basic idea is that, > if no explicit expiration time/age is provided, the cache uses a > heuristic to determine expiration, typically based on the > Last-Modified header. > > You have a few options here. If you'd like to force the cache to > always validate the response with the backend, you can set the > "must-revalidate" cache-control directive. Somewhere before the call > to stale?: > > response.headers['Cache-Control'] = "public, must-revalidate" > > That tells the cache that it's not allowed to serve a stale response > and that it must validate its version with the backend. > > Alternatively, you can set the max-age directive to zero. This has > pretty much the same effect but looks a lot nicer because Rails has a > controller method for it: > > expires_in 0, :public => true > > Give those a shot and let me know what happens. I'm also not sure I > like that Varnish does heuristic expiration by default, even though > it's to spec. > > Thanks, > Ryan > > > > -- Cheers --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Heroku" group. To post to this group, send email to heroku@googlegroups.com To unsubscribe from this group, send email to heroku+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/heroku?hl=en -~----------~----~----~----~------~----~------~--~---
