Each server shard is a database of user's games. When you first create a game, your game is assigned one of our databases at random (unless you're on the Development Server, which has its own dedicated Shard). This will be the shard your game will live on indefinitely. Firebase is what we use for our server infrastructure. They are very reliable. We don't see very many outages , but on the occasion when a shard goes down, there's not much one can do until the server issues are fixed and kicked back online again.