![]() However, even Subdomains can be decomposed further. Not every Bounded Context is a Microservice.Īligning Bounded Contexts with business subdomains is another popular heuristic for decomposing systems into Microservices. Therefore, A Microservice is a Bounded Context, but not vice versa. However, neither Domain-Driven Design in general, nor Bounded Contexts in particular, do not provide any guidance on how to do it.Ī big monolith and a small monolith, from Domain-Driven Design perspective, are perfectly valid Bounded Contexts, as long as they don’t have any conflicting models in them. But if you decompose the Bounded Context further, you’ll find those sought-after Microservices. Those will be “good” monoliths, since there won’t be any conflicting models in them, but still, they are not Microservices. If you follow the Bounded Context strictly, you will get monoliths. If you cross the boundary, those conflicting models will eventually lead to a big ball of mud. In the context of Microservices, it means one simple thing: a Bounded Context is the exact opposite of a Microservice!Ī Bounded Context defines the boundaries of the biggest services possible: services that won’t have any conflicting models inside of them. What does it all mean in the context of Microservices? Microservices A model is only valid in its Bounded Context. Those are two different models, and thus belong to two different Bounded Contexts.įinally, since in Domain-Driven Design the language is the model, and vice versa, each Bounded Context defines the applicability context of a specific model. For example, an Advertising Campaign is a complex entity with many rules and invariants for campaign managers but for sales agents, an Advertising Campaign is merely a data structure that describes a subset of its metadata. Second, different stakeholders might represent the same business entity in different models. Others understood “meter” as the connection between the grid and the customer, or, of course, a physical meter attached to a house to measure electrical consumption. ![]() In one department, it referred to the connection between the grid and a location. Martin Fowler has a nifty example of such a case: He relates how, when he worked for an electrical utility, the word “meter” had different meanings in different parts of the organization. First, the same term might describe completely different things. Those “meanings” can differ in multiple ways. Outside of it, the language’s terms may have different meanings. ![]() It defines a boundary, inside of which a Ubiquitous Language can be used freely. This context is called a Bounded Context. To overcome this hurdle, DDD requires each language to have a strict applicability context. Unfortunately, that’s not how human languages work - words often have different meanings in different contexts. Since software doesn’t cope well with ambiguity, each Ubiquitous Language term should have exactly one meaning. Bounded Contextsĭefining a Ubiquitous Language is not a trivial task. The Ubiquitous Language becomes the model of the business domain implemented in code. Even the code should “speak” the Ubiquitous Language as well. All communication should be done in the Ubiquitous Language, and all documentation should be formulated in it. The Ubiquitous Language should be extensively used throughout the project. This language should resemble the business domain, its terms, entities, and processes. To allow for the fluent sharing of knowledge, DDD calls for cultivation of a shared, business-domain-oriented language: Ubiquitous Language. DDD aims to increase the success rates by bridging this collaboration and communication gap. In “Domain-Driven Design: Tackling Complexity in the Heart of Software”, Eric Evans argues that poor collaboration between domain experts and software development teams causes many development efforts to fail. Crash Course in Domain-Driven Design and Bounded Contexts Not only is this heuristic flawed, but Bounded Contexts are the exact opposite of Microservices! To explain this point of view, I’ll start with a quick refresh of what Bounded Contexts are then I’ll discuss the relationship between Bounded Contexts and Microservices. I’ve always considered Domain-Driven Design’s Bounded Context as a guideline for defining the boundaries of Microservices.
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