Context

Microservices must be composed to provide users with complex and elaborated functionalities. It seems that the decentralized nature of microservices makes a choreography style more appropriate to achieve such cooperation, where lighter solutions based on asynchronous events are generally used. However, a microservice composition based on choreography distributes the flow logic of the composition among microservices making further analysis and updating difficult, i.e. there is not a big picture of the composition that facilitates these tasks. Business Process Model and Notation (BPMN) is the OMG standard developed to represent Business Processes (BPs), being widely used to define the big picture of such compositions. However, BPMN is usually considered in orchestration-based solutions, and orchestration can be a drawback to achieve the decoupling pursued by a microservice architecture.

Objective

Defining a microservice composition approach that allows us to create a composition in a BPMN model, which facilitates further analysis for taking engineering decisions, and execute them through an event-based choreography to have a high degree of decoupling and independence among microservices.

Method

We followed a research methodology for information systems that consists of a 5-step process: awareness of the problem, suggestion, development, evaluation, and conclusion.

Results

We presented a microservice composition approach based on the choreography of BPMN fragments. On the one hand, we propose to describe the big picture of the composition with a BPMN model, providing a valuable mechanism to analyse it when engineering decisions need to be taken. On the other hand, this model is split into fragments in order to be executed through an event-based choreography form, providing the high degree of decoupling among microservices demanded in this type of architecture. This composition approach is supported by a microservice architecture defined to achieve that both descriptions of a composition (big picture and split one) coexist. A realization of this architecture in Java/Spring technology is also presented.

Conclusions

The evaluation that is done to our work allows us to conclude that the proposed approach for composing microservices is more efficient than solutions based on ad-hoc development.

中文翻译：

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基于BPMN片段编排的微服务组合方法

语境

微服务必须组成为用户提供复杂的功能。看起来，微服务的分散性质使编排样式更适合实现这种合作，在这种合作中，通常使用基于异步事件的较轻的解决方案。但是，基于编排的微服务组合会在微服务之间分配组合的流程逻辑，从而使进一步的分析和更新变得困难，即，组合的概况不大，无法完成这些任务。业务流程模型和表示法（BPMN）是为表示业务流程（BP）而开发的OMG标准，被广泛用于定义此类组合的总体情况。但是，通常在基于业务流程的解决方案中考虑BPMN，

目的

定义微服务组合方法，该方法允许我们在BPMN模型中创建组合，这有助于进一步分析以做出工程决策，并通过基于事件的编排执行它们，从而在微服务之间具有高度的去耦性和独立性。

方法

我们遵循的信息系统研究方法包括5个步骤：对问题的意识，建议，开发，评估和结论。

结果

我们提出了一种基于BPMN片段编排的微服务组合方法。一方面，我们建议使用BPMN模型来描述构图的整体情况，为需要采取工程决策时提供一种有价值的机制进行分析。另一方面，此模型被分为多个片段，以便通过基于事件的编排形式执行，从而提供了这种架构所需的微服务之间的高度去耦。此组合方法由微服务架构支持，该微服务架构定义为实现对组合的描述（大图和拆分图）共存。还介绍了Java / Spring技术中该体系结构的实现。

结论

通过对我们工作的评估，我们可以得出结论，提议的微服务组合方法比基于临时开发的解决方案更有效。