XMPP servers can handle hundreds of users basically out of the box. Really good ones can easily go to a few thousands. The fun starts when your app gets traction and all of the sudden you have to handle tens of thousands, then hundreds, and with a blink of an eye - millions of online users. MongooseIM is built with scaleability in mind exactly for that case - your app starts small and then grows to match your imagination. Let’s explore the many ways in which you can make it scale. We will cover the impact of using bigger machines, different clustering techniques, benefits and challenges of multi-cluster setups. All those options have their traps and limitations, which we will explore in detail. You will also learn what we do on daily basis to monitor, maintain and improve MongooseIM's scalability.