How to Find the Right Places to Split a Monolith

They don't exist naturally. You must make them. Start with product comprehension: what does the product do? Why do customers buy it? Once you understand this, the data model and API endpoints reveal their hidden structure. Every product is fractal: it consists of smaller products, each with its own supply and demand.

The clearest signal is borrowed data from another domain. A user's full name stored in the orders table tells you two components are improperly joined. Another signal is margin. When the cost of maintaining a component exceeds the value it creates, that component needs a boundary change: split it, reorganize it, or kill part of it.