Cloudstate is ideally suited to the creation of small, isolated services, sometimes called Microservices. There are some patterns of Microservice architecture that are well-suited for Cloudstate services. For a more detailed discussion, see The Reactive Principles or the Reactive Architecture courses from Lightbend Academy.
As you build and deploy services, these design principles will be useful:
We recommend use of Domain Driven Design (DDD) to determine the best way to divide responsibility and state between services. Lightbend provides a free course on Domain Driven Design. See the information on determining service boundaries in the "Decomposing the Domain" chapter, "Identifying Bounded Contexts" section.
Each service you create should emphasise isolation--the service should be able to stand alone.
It is best to have each service deal with a single entity. If you have more than one entity, it is not possible for Cloudstate to route the data events optimally across the system.
Your service must not update its in-memory state directly as a result of a command. The handling of a command, if it results in changes being required to state, should emit events to Cloudstate. These events will then be received, at which point the in-memory state can and should be changed in response.
When you need to read state in your service, ask yourself what events should I be listening to. When you need to write state, ask yourself what events should I be emitting. See Event sourcing for more information.
A design issue you should plan for is the evolution of your message schemas. Commands and events have a definition, which amounts to a schema, and this schema often needs to evolve over time. Fields get added, fields get removed, the meaning of fields may change.
How do you handle this over time as your system grows and evolves?
Protocol Buffers offers a number of facilities that support evolution and migration across versions, but it is something that must be planned and handled carefully, so new versions of services don’t have problems reading older event journals that they can’t understand.