When building cloud applications, you need APIs to expose logic or data that other users, applications, APIs, or services can use. This is an integral part of a sound microservices architecture and engineering.

Hybrid cloud services that facilitate development and evolution of these service APIs include service API gateways that can limit or control API access, services to secure ingresses to services and APIs, tools and services to document and test APIs, in addition to the ability to meter and charge for APIs.

There are many reasons why a microservices architecture should expose services APIs, including:

When exposing APIs, there is a common set of tasks and a common high-level architecture. The steps include figuring out what part of the service or application or data that needs to be exposed as a service. This is called API design. The output of this step is an Open API document listing the different endpoints, the methods exposed (i.e., POST, PUT, GET), and the data structures in and out of these methods.

After the design phase, you need to generate the stubs and skeletons for the API document and connect that to the backend code that implements the API methods and consume and return the necessary data structures.

Finally, you need to plan for non-functional attributes for the API and deployment. An API Gateway is an excellent means to achieve this last step. Many cloud providers have API Gateways readily available to use. You can also deploy your own. The next sections highlight examples of these depending on the targeted cloud or open source projects you can use if you want to deploy your own.