This is big news for Node.JS; I'm surprised this hasn't gotten more attention. Hopefully Groupon will follow up with some more technical details of their transition from Rails to Node.JS and how they evolved their SOA architecture.
Looks like they moved only the frontend from Rails to Node.js. Rails still existing in their SOA architecture and they still using Ruby/JRuby hardly.
That is true. However, while we still have plenty of RoR code, a lot of our services have moved to Java and Scala.
I work at Groupon. We'll be following up with more details soon!