Redhat's popular open-source PaaS sooution, OpenShift, has recently responded to community requests for WebSockets on OpenShift.   OpenShift Evangelist Marek Jelen described some of the challenges that came with the implementation.  From the OpenShift Blog:  

For OpenShift as a PaaS provider, WebSockets were a big challenge. The routing layer that sits between the user's browser and your application must be able to route and handle WebSockets. OpenShift uses Apache as a reverse proxy server and a main component to route requests throughout the platform. However, Apache's mod_proxy has been problematic with WebSockets, so OpenShift implemented a new Node.js based routing layer that provides scalability and the possibility to expand features provided to our users.

The second thing that is problematic is the backend. WebSockets by default will work fine only with Node.js and DIY cartridges. Yeah, I know, it's pain ... but bear with me and let me explain a bit why this problem occurs.

You can sign up for OpenShift Online here.