I need to write server side for game ( communication between players, transporting data). Game is RTS. I need advice/opinion what to use to develop server side ? ( I am c++/java/python programmer but I have a little experience with Node.js and Clojure, a developing time is not a problem, I have time to learn something new).
If the game is real-time (as in Real Time Strategy) you should really consider node.js. Node provides great real-time integration, especially together with socket.io, which provides an easy and transparent WebSocket interface with gracefull fallback to Flash and Long-Polling.
Also, since you will need to simulate the game on the client (latency issues) as well as on the server (the authority simulation), you will need the same code on the server as well as on the client. Since you can only use JavaScript on the client, it is convenient to share some of the simulation code with the server instead of having to rewrite everything.
If you want to dig into web game developpment, you should watch this video from the last Google I/O : https://developers.google.com/live/shows/ahNzfmdvb2dsZS1kZXZlbG9wZXJzcg4LEgVFdmVudBjb9NgCDA/
It's a technical demonstration of Grits, an open source PvP game built with HTML5, developped by Google.
They speak about the technologies they used, such as node.js and websockets (with socket.io).
They also briefly explain some algorithms related to collision detection and latency issues. This part is essential, because it's applicable to any languages you're gonna use.
These technologies are fairly new, but seems to work well.
I'm personnaly building a real time game with socket.io, it's really fun and easy to play with. I'm also using Heroku, which is a great and free plateform for developpment purposes. This plateform let you concentrate only on your developpment, avoiding system administration headaches.
You can also consider Google App Engine using python. It has a channel API similar to socket.io which can let your players communicate without polling.