Developing a DDD-Oriented Microservices
The key principles and steps involved in developing DDD-oriented microservices
Microservices architecture and Domain-Driven Design (DDD) are predicted to continue gaining significant popularity in software development. Combining these powerful approaches enables teams to build scalable, maintainable, business-aligned systems.
In this article, we will explore the key principles and steps involved in developing DDD-oriented microservices, allowing you to harness the benefits of both paradigms. Let’s delve deeper into these concepts using Bit as the reference.
What is Domain-Driven Design (DDD)?
Domain-Driven Design (DDD) is an approach to software development that emphasizes modeling software based on the domain it serves. It involves understanding and modeling the domain or problem space of the application, fostering close collaboration between domain experts and software developers. This collaboration creates a shared understanding of the domain and ensures the developed software aligns closely with its intricacies.
What are microservices?
On the other hand, microservices are an architectural style that organizes an application into small, loosely coupled, and independently deployable services. Each microservice targets a specific business capability and can be developed, deployed, and scaled independently. They promote modularity, scalability, and agility in software development.
Why should we combine DDD with microservices?
Combining DDD with microservices architecture can be highly beneficial for building complex, scalable, and maintainable software systems. DDD and microservices complement each other and address different aspects of software development, making them a powerful combination. Here are the key reasons why combining DDD with microservices is advantageous:
- Bounded Contexts and Microservices Boundaries: DDD introduces the concept of bounded contexts, which defines the boundaries of a domain model and encapsulates its logic. These bounded contexts align well with the idea of microservices, where each microservice represents a specific bounded context. This alignment helps in defining clear and independent responsibilities for each microservice, promoting better modularization and separation of concerns.
- Decentralized Data Management: In microservices, each service is responsible for its data. DDD’s emphasis on aggregates, entities, and value objects encourages a decentralized data management approach, where each microservice has its data store that corresponds to its bounded context. This isolation of data aligns with DDD principles and enhances service autonomy.
- Model-Driven Development: DDD promotes a deep understanding of the domain and its complexities. By applying DDD, developers can create a rich domain model that captures the intricacies of the business domain. This model-driven approach ensures that each microservice has a well-defined and domain-focused purpose, leading to a more maintainable and expressive system.
- Ubiquitous Language: DDD advocates using a ubiquitous language that is shared between domain experts and developers. When combined with microservices, the ubiquitous language facilitates better communication between teams responsible for different microservices. It ensures a common understanding of domain concepts and fosters collaboration.
- Scalability and Loose Coupling: Microservices provide inherent scalability due to their decentralized nature. DDD’s emphasis on defining aggregates and bounded contexts allows microservices to be independently scalable, reducing dependencies and promoting loose coupling between services.
- Evolutionary Architecture: Both DDD and microservices advocate for evolutionary architecture. DDD allows the domain model to evolve with the changing business requirements, while microservices’ modular nature enables individual services to evolve independently without affecting the entire system.
- Continuous Delivery and Deployment: Microservices’ smaller and independent codebases facilitate faster and more frequent deployments. DDD’s emphasis on clear boundaries and modular design ensures that changes in one microservice have minimal impact on others, making continuous delivery and deployment easier to achieve.
- Team Autonomy: By aligning microservices with bounded contexts, teams can take ownership of individual microservices, promoting team autonomy. Each team can focus on its specific domain and implement business logic effectively, leading to improved productivity.
While the combination of DDD and microservices offers many advantages, it’s important to note that implementing both approaches requires careful consideration and understanding of the domain. Building a successful system using DDD and microservices demands a collaborative effort between domain experts, developers, and stakeholders to achieve a well-designed, scalable, and maintainable architecture.
How microservices fit into the DDD methodology?
DDDemphasizes modeling software based on the domain it serves.
We explore the core concepts of DDD, including bounded contexts, aggregates, entities, value objects, and domain services. By understanding these principles, you can effectively identify the boundaries of your microservices and design them around the business domains they represent.
Let’s delve into the key principles and steps in developing DDD-oriented microservices with an example of an e-commerce application
Implement DDD Oriented Microservices
Microservices architecture offers a way to structure an application as a collection of loosely coupled services, where each service runs independently in its process and communicates through lightweight mechanisms. In our e-commerce example, each bounded context can be implemented as a distinct microservice.
For instance, we can have microservices dedicated to “Order Management,” “Product Catalog,” “Payment Processing,” and “User Management.” Bit supports this approach by providing tools for creating and managing microservices through component-based development.
1.Understanding the Domain
In DDD the initial step involves thoroughly understanding the domain. This necessitates collaborating with domain experts to identify crucial business concepts, relationships, and behaviors.
In our example, the [core domain](Generic Subdomains) might be “Product Catalog” . This entity serve as our system’s fundamental building block, encapsulating behavior and state. As in the above image Product Catalog is marked as “Core subdomain”, that represents the main part of the Domain. In this case, Because it is what customers will be interacting. Others Subdomains were classified as Support and Generic.
To facilitate this step, Bit offers a collaborative platform where domain experts and developers can collaborate on defining and documenting domain models, capturing business rules, and sharing knowledge. Bit’s collaboration features, including shared workspaces, version control, and documentation support, foster effective communication and knowledge sharing between domain experts and developers.
Source : https://bit.cloud/bit/evangelist/sections/build-together?example=5ee51e53c166fb0019182a29
Support subdomains function as auxiliary domains within the overall system. In practice, you define a Bounded Context for them and create a dedicated application that serves as a support system for the Core Domain application. Despite being supportive, these applications maintain their own distinct model.
On the other hand, [Generic Subdomains](Generic Subdomains) share similarities with support subdomains, but with a significant difference. They offer solutions that are so versatile that they can be utilized not only within the specific Domain they were created for but across other Domains as well. For instance, a well-designed “Access Control Application” might be easily repurposed to support domains beyond e-Commerce. That is precisely why they are referred to as Generic Subdomains.”
2. Bounded Contexts
In Domain-Driven Design (DDD), the domain is divided into bounded contexts, which act as logical boundaries encapsulating specific domain areas. Each bounded context represents a separate subsystem within the application.
Microservices align harmoniously with bounded contexts in DDD as they offer a natural approach to implementing and deploying each context as an individual service.
In our e-commerce application, we may have bounded contexts such as “Order,” “Product Catalog,” “Payment,” Inventory, Shipping and “User Management Authentication and Authorization”. Bit facilitates providing tools for defining and managing the boundaries of bounded contexts. Below diagram depicts the main contexts of the e-commerce application.With Bit’s component-driven development approach, developers can encapsulate and manage the functionality of each bounded context as independent components. These components can subsequently be deployed as microservices.
3. Aggregate Design
Aggregates serve as consistency boundaries within the domain, encapsulating clusters of related entities and value objects. They guarantee data consistency and establish clear boundaries for enforcing business rules.
- How does one decide on aggregates?
Deciding on aggregates in DDD involves identifying the boundaries of consistency and transactional integrity within your domain model. Aggregates are clusters of related entities and value objects that are treated as a single unit, ensuring that changes to one part of the aggregate maintain the consistency of the whole.
- Are there key characteristics that define an aggregate?
Yes, there are key characteristics that define an aggregate in DDD. An aggregate is a fundamental building block in DDD, representing a cohesive unit of domain objects that are treated as a single entity with well-defined boundaries. Here are the key characteristics that define an aggregate:
- Consistency Boundary: An aggregate represents a consistency boundary within the domain. The aggregate ensures that the state of its internal objects remains consistent and valid.
- Aggregate Root: Every aggregate has a designated “aggregate root” that acts as the entry point to the aggregate.
- Transaction Boundary: Changes to an aggregate are made within a single transaction. The entire aggregate is treated as a single unit of work, ensuring that either all changes succeed or none at all.
- Encapsulation: The internal structure of the aggregate is hidden from external entities.
- Invariant Enforcement: Aggregates enforce invariants, which are the rules and constraints that must hold true within the aggregate. Invariants ensure that the aggregate remains in a valid and consistent state during and after any operation.
- Lifecycle Management: Aggregates manage the lifecycle of their internal objects. For example, creating, updating, and deleting entities and value objects should be done through the aggregate root, which maintains control over these actions.
- Boundary for Communication: Aggregates serve as boundaries for communication and consistency between different parts of the domain model. Changes to one aggregate do not directly affect other aggregates, which helps in maintaining modularity and reducing coupling.
- Granularity: Aggregates should have a proper granularity, meaning they should be neither too large nor too small. They should be designed to manage a meaningful set of related domain concepts and operations.
Understanding and adhering to these key characteristics of aggregates is crucial to successfully applying DDD principles and building well-structured domain models in complex software systems.
In DDD, microservices can align with aggregates by implementing each aggregate as an individual microservice. In our example, the “Order” aggregate may comprise objects such as “OrderItem,” “Customer,” and “ShippingAddress.”
Bit facilitates this process by offering tools for designing and managing aggregates as reusable components. Developers can define aggregates as components in Bit and leverage its versioning and dependency management features to ensure consistency and modularity across microservices.
## 4.Communication and Integration
Communication and integration between services are vital in a microservices architecture. Services must interact and exchange information to accomplish business processes.
5.Deployment and Scaling
Microservices offer the advantage of independent deployment and scaling, allowing each microservice to be deployed and scaled individually based on its specific requirements. This flexibility and scalability are crucial in modern software development.
Conclusion
In conclusion, developing DDD-oriented microservices entails a comprehensive understanding of both DDD principles and microservices architecture.
By adopting DDD, identifying bounded contexts, and aligning microservices with aggregates, you can construct systems that are scalable, maintainable, and closely aligned with your business needs. It is crucial to continuously iterate and refine your architecture, incorporating domain expertise and feedback. This iterative approach ensures that your microservices evolve and adapt over time, keeping pace with the changing needs of your business. By combining the power of DDD and microservices, you can create robust and adaptable software systems that drive your organization forward.
