How to share java models between microservices in microservice architecture

Question

I am designing the architecture of my new app.I chose microservice architecture.In my architecture I noticed that I have models that are used by diffrent microservices. I want to know if there is a way to share models code between microservices instaed of writing them in each microservice.

By the way I am using the spring boot framework for my app.

Answer 1

You should only be sharing models that define the API of your micro-service eg Protobuff .proto files or the Java classes generated from them.

This is normally done by creating either a separate project or converting your micro-service projects into a multi-module projects where one of the modules is a thin API module with interface definition.

There is nothing wrong in sharing code between micro-services but you have to be careful. Share too much internal implementation details and you end up with a distributed monolith instead of micro-services .

Answer 2

In a Microservices architecture, each one is absolutely independent of the others and it must hide the details of the internal implementation.

If you share the model you are coupling microservices and lose one of the greatest advantages in which each team can develop its microservice without restrictions and the need of knowing how evolve others microservices. Remember that you can even use different languages in each one, this would be difficult if you start to couple microservices.

https://softwareengineering.stackexchange.com/questions/290922/shared-domain-model-between-different-microservices

Answer 3

您可以将模型类移动到不同的项目/存储库，并将其作为依赖项添加到需要共享它的微服务中。

Answer 4

You can create a separate project with common models, create a jar of this project and add dependency of this jar in other microservices.

But I have a practical experience, its a nightmare to maintain this common project, because for every change you have to create a new version and update the build scripts of all the microservices.

In my opinion we should not share models among the microservices.

Answer 5

If you are draconian about this decision you will run into unsatisfactory conditions one way or the other. It depends on your SDLC and team dynamics. At Ipswitch, we have many services that all collaborate and there are highly shared concepts like device and monitor. Having each service have its own model for those would be unsustainable. We did that in one case and the translation just created extra work and introduced inconsistency defects. But that whole system is built together and by one large dev team. So sharing makes the most sense there. But for an enterprise, where you have multiple teams and multiple SDLCs across microservices, it makes more sense to isolate the models to avoid coupling. Even then, however, a set of closely collaborating services that are managed by a given team can certainly share a model if the team accepts the risk/benefit of doing so. There is nothing wrong with that beyond academics and philosophy.

So in short, share minimally but also avoid unnecessary work for your team.

Answer 6

Not sure if your microservices use Swagger, but, you can use Swagger Codegen to generate your models.

For example, If you have UserService which accepts and/or returns User object. The consumer of UserService can use the Swagger Codegen plugin to auto-generate the User class at build time.

You can use Swagger Codengen maven or gradle plugin pretty easily.