[kumaraman]

Domain driven design from Eric Evans is a great resource for learning about how/where to separate out services.

You will learn about how to model complex domain models and how to decompose them into Aggregate's. The Aggregate is the key to where to create new microservices, as each aggregate should only contain domain objects that relate to itself.

Payments is a great example of an Aggregate.

[meekins]

I'd say a bounded context is a better border. When doing REST you can then begin by implementing each of your aggregate roots within the context as a resource.

[kumaraman]

I've never been able to make sense from including more than one aggregate root in a bounded context. What are your thoughts?