May be not as much clear. But Ruby world has plenty of options for Websocket as well. I have built production Websocket server on top of Goliath and Faye and it works like a charm.
Yeah, it's not like it's impossible with Ruby, but especially compared to a system like Erlang - to my way of thinking - it can start to look a bit clunky when you try and get lots of pieces talking to one another if, say, most of the rest of the application is in Rails. Or at least that's my impression, maybe I'm wrong?
I daresay you seem to have wrong impression. Having Rails app for typical web stuff and Eventmachine (em-synchrony) + faye stuff for realtime things work pretty well in actual usage. I can wrap DB calls, memcache/redis, SMTP connections etc inside my event loop and can achieve near same performance as a Node app.
The alternative of using node.js for everything sounds good but I am not really sure, how good node and its web frameworks are for building typical CRUD applications. Rails really solves building database backed applications problem pretty well.
I receive some kind of request in a Rails controller. I need to send, as a consequence, a notification via the web socket. How does it get from point A to point B? In Erlang, it's all likely to be quite contained and fast, and not involve writing anything to external queueing software, and to boot, it's all going to happen in the same unix process, rather than having one process that's the Rails server, and another that's the eventmachine server.
I don't know Node.js and how you'd handle sending messages from point A to point B, but I'd be interested in hearing some opinions.
https://github.com/faye/faye-websocket-ruby
Faye is the the most feature complete websocket implementation out there and it works quite well.