Consumer driven contracts (CDC)

Consumer-Driven Contracts (CDC) is a technique for testing microservices in a distributed system, where the consumers of a service define the contracts that the service must adhere to. This approach allows for testing the interactions between services in a way that is decoupled from the implementation of the service itself.

In CDC, the consumers of a service, such as other microservices, define a set of contracts, or test cases, that describe the expected behavior of the service. These contracts are typically defined in the form of request-response pairs, where a request is sent to the service and the expected response is specified. The service provider then implements the service and runs the contracts against the service to ensure that it adheres to the contracts defined by the consumers.

One of the main benefits of CDC is that it allows for testing the interactions between services in isolation, without having to run the entire system. This can make testing more efficient and effective, as well as make it easier to identify and fix issues that arise during integration testing. Additionally, CDC helps to ensure that changes to a service do not break existing consumers of the service, by testing the compatibility of the service with the consumers contracts.

There are several open-source and commercial tools available to help developers implement CDC in their microservices. Some of the popular CDC tools are:

  1. Pact: Pact is an open-source framework that allows developers to define, test, and publish contracts between services. It supports multiple programming languages and message formats, and it can be integrated with various test runners and CI/CD pipelines.
  2. Spring Cloud Contract: Spring Cloud Contract is a library for Spring Boot applications that allows developers to define and test contracts for HTTP and message-based interactions. It integrates with Spring Cloud Sleuth and Zipkin to provide distributed tracing capabilities, and it can be used with a variety of messaging and HTTP clients.
  3. Contract Testing: Contract testing is a tool developed by Postman, it allows you to define and test contracts between APIs and microservices. It supports contract testing in a variety of formats, including OpenAPI, Postman collections, and Pact files.
  4. WireMock: WireMock is a library that allows developers to create HTTP-based APIs for testing purposes. It can be used to mock out third-party services and test the interactions between services in isolation.
  5. Pactflow: Pactflow is a tool that allows teams to manage and automate the contract testing process by connecting pact tests to CI/CD pipelines. It also helps with version management and publishing of contracts.

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