[sync]

That's not true. Google Analytics cookies are injected via JS. When heroku's Varnish is checking for a cached version of the page, it strips any cookie information given by the browser.

We've are running production apps with Varnish caching + Google Analytics without issue.

Set your cookies with JS or on uncached pages (such as POST logins) and you'll be fine.

[mrkurt]

It's possible that it strips the GA cookies (which is cool, I had no idea), but Varnish doesn't strip cookie information from the browser. If it did you wouldn't get any Rails sessions or anything.

[sync]

It's not specific to GA cookies.

You can set cookies on uncached pages in ruby and read them without issue in JS on Varnish cached pages. The page will still be cached even if the user has a session cookie.

Basically: don't set or get cookies in ruby on cached pages and you'll be fine.