Game is based on JavaScript/Canvas and WebSockets. On the browser side the map is pre-rendered (as a background image), just the mobile units/buildings and animations are dynamically rendered. The lobby server is made in node.js, but the game server is C++ for performance reasons (mainly the pathfinding). I found the C++ WebSocket libraries out there to be too difficult to use so I made my own based on the rfc. Overall I think making a game like this is quite easy with the browser performance/features nowadays. The game server and client side JavaScript are around 5000 lines of code each.

If you have any questions about the tech I'm happy to answer them.