Too Long; Didn't Read
We were using <a href="https://hackernoon.com/tagged/mysql" target="_blank">MySQL</a>: one master for writing, and a few slaves for reading. Besides <em>replication lag</em> (more on that later), it worked fine. And then you scale. And then it fails! The master is a SPOF — “<strong>S</strong>ingle <strong>P</strong>oint <strong>O</strong>f <strong>F</strong>ailure”.