How do you design service contracts to support loose coupling and evolution?

1 Define clear and consistent boundaries

The first step to design service contracts is to define clear and consistent boundaries for each service. Boundaries are the logical and physical separation of services that enable autonomy, cohesion, and encapsulation. You should identify the business capabilities, functions, and data that each service provides and consumes, and avoid overlapping or conflicting responsibilities. You should also define the scope, granularity, and visibility of each service, and avoid exposing unnecessary details or dependencies.

2 Use standard and interoperable formats

The second step to design service contracts is to use standard and interoperable formats for the messages, data, and protocols that each service uses. Formats are the representation and communication of information between services that enable compatibility, readability, and validation. You should use widely adopted and industry-accepted formats, such as XML, JSON, SOAP, REST, or gRPC, and avoid proprietary or custom formats. You should also use schemas, metadata, and documentation to describe the structure, semantics, and constraints of each format.

3 Apply loose coupling and abstraction

The third step to design service contracts is to apply loose coupling and abstraction for the interactions and dependencies between services. Loose coupling and abstraction are the principles that reduce the coupling and increase the independence of services that enable flexibility, scalability, and evolution. You should use loosely coupled and abstract interfaces that hide the implementation details and expose only the essential functionality of each service. You should also use loosely coupled and abstract dependencies that minimize the assumptions and expectations of each service.

4 Support versioning and compatibility

The fourth step to design service contracts is to support versioning and compatibility for the changes and updates of services. Versioning and compatibility are the practices that manage the impact and risk of changes and updates of services that enable innovation, maintenance, and quality. You should use versioning schemes and strategies that identify, communicate, and document the changes and updates of each service. You should also use compatibility rules and techniques that ensure the backward and forward compatibility of each service.

5 Implement policies and governance

The fifth step to design service contracts is to implement policies and governance for the compliance and enforcement of service contracts. Policies and governance are the rules and processes that regulate the creation, modification, and usage of service contracts that enable consistency, reliability, and security. You should implement policies and governance at different levels, such as design-time, run-time, and change-time, and use tools and frameworks, such as registries, repositories, or brokers, to support them.

6 Test and monitor service contracts

The sixth step to design service contracts is to test and monitor service contracts for the verification and validation of service contracts. Testing and monitoring are the activities that check the correctness, performance, and availability of service contracts that enable feedback, improvement, and troubleshooting. You should test and monitor service contracts at different stages, such as development, deployment, and operation, and use tools and methods, such as unit testing, integration testing, or contract testing, to perform them.

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?