Disadvantages to rack-cache vs. Varnish in Heroku cedar stack?

Question

The previous 2 Heroku application stacks came with a Varnish layer which automatically reverse-proxy-cached content based on http headers.

The new Heroku cedar stack doe

Answer 1

I don't know how the rack-cache performance compares to Varnish in terms of raw requests. The best bet would be to create a simple app benchmark it and switch stacks.

It's worth bearing in mind that because the heroku.com stack was Nginx->Varnish->App as long as you've set the correct HTTP headers you're App layer will be doing much less work. As most of the delivery will be handled by Varnish, as well as Varnish being pretty fast, this frees up your Dyno for actual app-handling-requests.

With the herokuapp.com stack hitting your app earlier, it's down to you and your app to handling caching efficiently, this might mean you choose to use rack-cache to cache full page output or you might choose to use memcached to deal with database requests or both.

In the end it depends on what your app is doing, if it's serving the same static content to a lot of users then you'd benefit from Varnish, but if you've got an application where users login and interact with content then you won't see might benefit from Varnish so caching partial content or raw database queries might be more efficient. If you install the New Relic addon you'll be able to take a peek under the hood and see what's slowing your app down.