API Standards

With the rise of Cloud, Microservices, and Cloud-native technologies, API development is one of the key focus areas for organizations – both from an internal and external integration perspective.

Services & API Standards Evolution
Figure A – Services & API Standards Evolution
OpenAPI - Standard for Request/Response based HTTP APIs

OpenAPI – Standard for RESTful APIs

OpenAPI specification (originally based on Swagger 2.0) has become the de facto industry standard for HTTP APIs providing the programming-language agnostic interface. Key highlights are:

Async API - Standard for Asynchronous Event-driven APIs

Async API – Standard for asynchronous event-driven APIs

Async API has started becoming the industry standard for defining asynchronous APIs. For event-driven and microservices architecture, asynchronous communication is the need of the hour and a common standard helps to build the semantics common understanding. Key highlights are:

  • An open source initiative targeted to improve the current state of Event-Driven Architectures (EDA).
  • Supports both JSON & YAML as message format and AsyncAPI document is a machine-readable for event-driven API. OpenAPI goal is to work collaboratively with other standards like OpenAPI, GraphQL, and gRPC definitions.
  • AsyncAPI is not a competitive specification to OpenAPI rather it is a collaborative specification. It emerged as an adaptation of the OpenAPI specification (see comparison below).
  • Click here to see the list of tools supporting as Code Generators, Documentation, Mocking & Testing, Validators, etc.

Cloud Events Logo

Cloud Events – Specification for describing event data

CloudEvents (part of CNCF now) is relatively new to create a specification for describing event data in common formats to provide interoperability across services, platforms, and systems. Key highlights are:

  • Emerging standard to support event-driven architecture focused primarily on events to decouple provider and consumer supporting interoperability between systems.
  • In comparison to Async API, Cloudevents focuses on message format than API itself and gets applied to FaaS (function-as-a-service) or any system exchanging event or message with a common industry format.
  • Async API and CloudEvents are not competing specifications can be used together.
  • Apart from event attributes and related metadata, it also focuses on how to serialize the event in different formats (e.g. JSON) and protocols (e.g. HTTP, AMQP, Kafka).
  • Supported by cloud event bus, and event-oriented solutions (including Serverless) such as Argo Events (Event-driven Workflow Automation Framework), OpenFaaS (Serverless framework to deploy event-driven functions and microservices to Kubernetes), Serverless Workflow (specification that defines a vendor-neutral and declarative workflow language), Google Cloud Eventarc (to build event-driven architectures with loosely coupled services that react to state changes), Azure Event Grid, Oracle Cloud Events, Alibaba Eventbridge, etc.


OpenAPI Example

openapi: 3.0.0
  description: OpenAPI Specification for the a Hello World API
  version: 1.0.0
  title: Hello World API
      summary: Provides hello world message
      operationId: Sends hello world message
      description: Provides a simple Hello World message using GET operation
        - name: user
          in: query
          description: Your name.
          required: false
            type: string
          description: Success
  - url: http://api.vedcraft.com

Async API Example

asyncapi: 2.1.0
  title: Hello world message
  version: '0.1.0'
          type: string
          pattern: '^hello .+$'

CloudEvents Message Example

    "specversion" : "1.0",
    "id" : "V123-456-789",
    "source" : "https://api.vedcraft.com/helloworld",
    "type" : "com.vedcraft.helloworld",
    "subject" : "message",
    "time" : "2021-08-30T09:05:00Z",
    "datacontenttype" : "application/json",
    "data" : "{\"fname\": \"ankur\", \"lname\":\"kumar\"}"



Leave a Comment