Distributed systems are really about persistent state. As soon as you have/need that, you run into these problems. If you need to deploy while maintaining state

Distributed systems are really about persistent state. As soon as you have/need that, you run into these problems. If you need to deploy while maintaining state (like DB contents), or fail gracefully without losing your entire DB, then you have entered the realm of distributed systems. These properties are present even in most "monoliths".