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Discussion on: To Domain Driven Design

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Kevin Mas Ruiz Author

Hi Vivien, thanks for your feedback! Let me try to answer and clarify your questions :).

1) Systems need to interact with other systems to remain useful and when there is interaction, there is some coupling. You can earn some benefits, like availability and team performance, when this coupling is temporary.

For example, if you have a CheckoutService and every time you want to buy a book you need to query the StockService (through a HTTP endpoint or any other way) you have direct coupling every time you need the information.

If you invert the communication, and the StockService or any other peer offers you updates on the stock through a broadcast mechanism, you don't mind if the StockService is down or not, you only need the updates in a place where you can read it and doesn't depend on the availability of the service. You need someone to provide the information, but you only need to agree just on the format and the quantity of information you need.

With Apache Kafka, for example, if you configure your partitions in a specific way (partition key = domain id) and you implement a state-sourcing mechanism, you don't even need any service to replay states when you implement new functionality because you can replay the state by yourself.

2) There is a book named Lean Inception written by a Thoughtworks colleague (Paulo Caroli) that uses the name MVP for defining products that can be deliverable in a predictive way. Those MVPs are bound to a set of personas (you focus on solving the problems of a single type of user), a set of user journeys for that personas, and you define an autonomous way to measure the success of the MVP.

This mechanism (that's from my side, not part of the book) allows business to define a set of products that have a relationship between them and can be evolved independently of other products. You usually will build new products when you want to widen the impact of your platform or experiment on new business slices, and you will implement new features on a MVP when you want to optimize the revenue you have from an already known subset of personas.

Thinking in a business as a "platform" of products allows us to define boundaries that are relevant for the business, autonomous, and have impact on business metrics. It's just a way of defining boundaries that is a bit different, but it doesn't necessarily mean it's right :D. I've used it a couple of times in different teams and it worked quite well.

Please feel free to follow up here if the answers were not clear enough.