1 What is DDD and why is it useful for microservices?

Domain-Driven Design (DDD) is an approach to software development that focuses on the domain, or the core business problem, and the language, or the common terms and concepts, used by the stakeholders and developers. DDD helps you to understand the domain better, to model it in code, and to align it with the architecture. For microservices, DDD is useful because it helps you to identify the boundaries, responsibilities, and interactions of each microservice based on the domain logic, not on technical or organizational factors.

3 How to map the relationships between bounded contexts?

Once you have defined the bounded contexts for each microservice, you need to map the relationships between them. These relationships describe how the bounded contexts interact, collaborate, or depend on each other. There are different types of relationships, such as partnership, customer-supplier, conformist, anticorruption layer, open host service, or published language. Each type of relationship has different implications for the communication between microservices, such as the level of coupling, the direction of flow, the format of data, or the frequency of changes. You need to choose the appropriate type of relationship for each pair of bounded contexts based on the domain logic and the communication requirements.

4 How to design the communication patterns between microservices?

After mapping the relationships between bounded contexts, you need to design the communication patterns between microservices. Communication patterns are the ways that microservices exchange data, commands, or events with each other. There are two main types of communication patterns: synchronous and asynchronous. Synchronous communication means that the sender and the receiver are both online and waiting for a response. Asynchronous communication means that the sender and the receiver are not necessarily online or waiting for a response. Each type of communication has its advantages and disadvantages, such as performance, reliability, scalability, or complexity. You need to choose the appropriate type of communication for each scenario based on the domain logic and the communication requirements.

6 How to evolve the domain model and the communication patterns between microservices?

The domain model and the communication patterns between microservices are not static, but dynamic and evolving. As the business needs change, the domain logic, the language, the rules, and the constraints may also change. Therefore, you need to adopt an iterative and incremental approach to design and implement the domain model and the communication patterns between microservices. You need to validate your assumptions, test your hypotheses, collect feedback, measure results, and learn from your mistakes. You also need to apply refactoring, versioning, or migration techniques to update or replace your microservices without breaking the communication or the functionality.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?