As a back-end for Solitaire and Mahjong games I’m using a separate VPS with Node.js, as a web server, and MySQL database, which I’m hoping to switch to MariaDB some day.
I really like Node.js, it can handle thousands of connections at once on a cheap VPS for ~$10/month.
On July 12 2013, All-in-One Mahjong was promoted on Amazon App Store as a Free App of the Day, and game had ~100k active players a day. But Node.js had absolutely no problems with that, even 512MB of memory was enough.
I’m very new to Node.js, so here are some links, that helped me to know it better:
Manual and Docs: http://nodejs.org/api/
Node.js driver for MySQL: https://npmjs.org/package/mysql