Practitioner Views on the Interrelation of Microservice APIs and Domain-Driven Design: A Grey Literature Study Based on Grounded Theory

Abstract

Microservice API design is a critical aspect in crafting a microservice architecture. While API design in general has been studied, the specific relation of API design to design practices and models commonly used in microservice architectures is yet understudied. In particular, practitioners frequently use Domain-Driven Design (DDD) in their microservice architecture and API designs. We thus decided to study existing Architectural Design Decisions (ADDs), their solutions options, their relations, and the decision drivers in these decisions. Using the Grounded Theory research method we studied grey literature sources. In this study, we identified six ADDs with 27 decision options, numerous relations between them, and 27 decision drivers. The decisions cover mapping domain models to APIs, defining API contracts in relation to domain models, designing API resources based on domain model elements, segregation of API resources, mapping domain model links to the API, and designing the operations of an API resource.

Patterns on Deriving APIs and their Endpoints from Domain Models

“…Figure 1 illustrates our research process and methods. The main knowledge sources used in this work have been gathered in two of our prior works [28,29]. In the first of those, we studied 32 practitioner sources from the grey literature in depth [29] using the Grounded Theory (GT) research method [5,13], a systematic research method for discovery of theory from data.…”

“…The main knowledge sources used in this work have been gathered in two of our prior works [28,29]. In the first of those, we studied 32 practitioner sources from the grey literature in depth [29] using the Grounded Theory (GT) research method [5,13], a systematic research method for discovery of theory from data. We studied each knowledge source in depth, followed GT's coding process, as well as a constant comparison procedure to derive a model of architectural decisions on deriving APIs and API endpoints from domain model elements.…”

“…Secondly, we conducted a Grounded Theory study based on the grey literature mainly focusing on the interrelation of microservice API design and DDD [29]. We derived six architectural design decisions (ADDs) with 27 design options and 27 design drivers.…”

“…Two other variants of domain model facade as api, as shown in Figure 7, are to Expose Each Bounded Context as its Own API [29] or Expose Selected Bounded Context as APIs [29]. These two practices select the bounded context as API scope.…”

“…Thus, the question arises how to derive APIs from DDD models. In our prior works, we investigated the interrelation of microservice API design and DDD [29], and DDD violations in the context of coupling smells [28]. Those smells and violations are especially problematic when used in distributed setting.…”