It seems Cookpad's claim of largest Rails Monolith may not be true anymore. (1) But I have known this for sometime when I heard China' Rails Ticketing System were built on Rails, then I assume peak traffic would be larger then Google + Twitter + Amazon Combined. Although they have moved off the Rails due to scaling issues.

I wonder if Shopify have any Ruby performance or Rails Scaling issues to share?

And the last thing is Rails just prove to be popular and works well for ( and may be only ) paid SaaS. It allows you to quickly iterate your product until you find a product / market fit. And once you have generate a revenue stream, the Server / Software Scaling Cost becomes relatively minor compared to Human Cost. But for those who are on a freeminum model and depends on Ads, Cost of running Ruby Rails may quickly out pace your budget before you have large audience to generate revenue.

1. https://speakerdeck.com/a_matsuda/the-recipe-for-the-worlds-...