I chose to use Node/Express at my last startup and Ruby on Rails at my current one. Both are great platforms with fantastic communities behind them. For example

I chose to use Node/Express at my last startup and Ruby on Rails at my current one. Both are great platforms with fantastic communities behind them. For example, there is an amazing amount of Stack Overflow answers and folks watching for new questions. It's important to note that Express, the most popular Node framework, is a clone of Ruby's Sinatra, not of Rails. That's a great back-end when your front-end is iOS or React and you have a relatively simple data model. But it's not as strong a solution if you need to do server-rendered pages (which we need to support IE8). The bigger issue is that Rails is just a much more mature and full-featured framework than Express or Sails.js (which is designed to be Rails for Node). From migrations to validations to strong parameters to many other areas, Rails just offers a ton of back-end functionality that is not as mature on Node frameworks. The big question is how much back-end business logic needs to be implemented. I haven't run into any issues with Ruby's server performance. AWS instances are easy to spin up, and any Ruby compute time is almost certainly going to be overwhelmed by network and database access. The performance we're focused on is developer productivity, and I think Ruby retains an advantage there over Javascript (though obviously we use both). If I were trying to support millions of simultaneous web socket connections, I would almost certainly go with Node (or maybe Go).