Among many of the software development approaches, Domain-Driven Design (DDD) is a strategy that eases communication, improves flexibility, and emphasizes Domain over the interface. Domain-Driven Design focuses on the growth and evolution of programming a domain model that has a strong knowledge of the methods and rules of a domain. It carefully structures the business domain in software.
The Domain-Driven Design assists the team to create a common model which can be used for both the business’ side and the developer’s side to communicate business requirements, the data entities, and process models. The domain model consists of objects. Due to this reason the system can be changed and improved regularly and continuously.
The Layout of Microservices and Domain-Driven Design and their Relation
As we all know, applications can be created from loose coupling services, i.e. with the help of microservices, where each microservice has a unique task and a business goal. These microservices can be developed and simply controlled separately. Later they can be connected to produce a complex application.
A microservice is a basic architecture design model with a particular bounded context, configuration, and dependencies which resulted from the architectural theories and concepts of the Domain-Driven Design and DevOps. For that reason, microservices hold an involving interaction with the Domain-Driven Design approach as it is utilized to describe various bounded contexts that portray the different business processes that the application requires to carry out. Domain-Driven Design is the concept of resolving difficulties and issues of the organization via code.
Domain-Driven Design for Assembling and Decoupling Microservices
Domain-Driven Design is a strategy that can be used to develop complex systems in the business domain that unravel real-world business problems. In other words, it is a significant approach to partition the business model methodology and the code that connects everything, in a software application. This helps to map out, structure, develop, and build a software application successfully with time.
Domain-Driven Design is set up on the concepts which are given below:
- Acquire the domain model, in domain terms, via connections with domain experts
- Set the domain utilization in the code
- Secure the domain knowledge from deception by other domains and technical subdomains.
Most complex business software projects consist of various domain models and bounded contexts. When bounded contexts that are coded differently are put together and merged, the software application might operate with faults, and turn out to be unreliable and inconvenient to comprehend. Connections between team players will confuse, and it will frequently not be clear to see in what context a model should not be applied.
With this, the Domain-Driven Design approach recommends outlining the context within which a model is applied and setting up boundaries in terms of,
- Which team holds that specific model.
- Utilization of particular components of the software application.
- Physical displays such as database schemas and code bases.
Persevering the models precisely stable within the bounds will make every part simpler to develop and comprehend as it is required to pay attention to a single bounded context only. Every microservice consists of a bounded context that involves numerous APIs, frameworks, datastores, and communication protocols. Some of them deal with the request-response pattern, and the rest will make use of events such as Kafka relying on the problem that requires to be fixed. Nevertheless, all will be distinct bounded contexts and include a distinct domain model and mappings between that model, business processes, and the data it shares with others.
Layers in Domain-Driven Design microservices
The majority of business software applications are technically complex. These applications consist of multiple layers. These layers are logical artifacts. Due to that reason, they are not associated with the deployment of the microservices. Instead, their task is to assist software developers to handle and deal with the complexity of the code.
User Interface plays a major role in a software application apart from the layers in a Domain-Driven Design associated with microservices. User Interface is the component where the user of the application finds all the information required to handle and deal with the system. Hence the User Interface can be considered as the frame of the layers in the Domain-Driven Design model.
Let us have a look at each layer in the Domain-Driven Design model.
Application layer: The application layer is the top-most layer out of the three layers and it does not include the business logic. It’s the layer that guides the customer through the User Interface and its screens. Even though the application layer is capable of executing simple validation tasks, it does not contain any domain-related logic or data access. It is the only layer accessible to other bounded contexts. The function of the application layer is to coordinate and authorize domain objects to perform their tasks.
Domain layer: The domain layer consists of business concepts and entities (data and behavior). For that reason, this layer consists of all the information related to the business use case and its rules. The entities consist of distinctive identity undertaken through a unique key and continue to exist the same even when their properties amend. The value objects do not consist of unique identifiers as they exhibit properties that numerous entities can share.
The domain layer is considered to be the most important layer out of the three layers as it the center of the software application and it includes services outlined with operational behaviors having no connections with a part of any domain. Yet, they are a part of the business domain. The domain layer must be detached from the other layers and the User Interface. In addition, it must not depend on other layers and their frameworks.
Infrastructure layer: The infrastructure layer assists connections in between the other layers and it consists of supporting libraries for the User Interface.
Best Practices to Leverage Domain-Driven Design for Microservices
The Domain-Driven Design approach permits us to write quality code efficiently. It also can be considered as a great software design technique to comprehend and resolve the complexity of software applications. In summary the best practices to leverage domain-driven design for microservices approach describes the problems of a software application as domains and subdomains and it explains unique sections of problems as bounded contexts.