How do you document and enforce API policies and contracts?

API policies and contracts serve as foundational elements that define the rules, expectations, and standards guiding the design, implementation, and utilization of an Application Programming Interface (API). These essential components play a crucial role in ensuring consistency, security, and effective collaboration among developers, organizations, and systems interacting through APIs.

One of the best embedded documentation tools / contract guidelines mechanisms within the API responses is HATEOAS (Hypermedia As The Engine of Application State). HATEOAS allows a developer to use the endpoint itself to 1) see navigational links to traverse the aggregated entities, 2) understand the schema of the entity, and 3) see sticky links/URLs for the called API in its response objects. HATEOAS provides invaluable embedded help to developers to learn about the endpoints and API structure, without making them leave their favorite API integration tool or IDE.

API can be loosely thought of as an exchange, where you can exchange data. There are some rules and regulations that governs the exchange. A sample exchange rule can be: To get the number of employees as an integer for a department from an API, you need to send a request with a payload that has the department name, and a header that has a token with authenticates the request and authorizes it to use the API.

We document our APIs using OpenAPI specification, which provides a clear contract for the API endpoints, request/response types, and error messages. We enforce these contracts using tools like Swagger UI for interactive documentation and Dredd for contract testing. API policies such as rate limiting or authentication requirements are enforced at the server level and are also documented in our API documentation.

They are important because they set the standards to be followed in the organization and keep the coherence and consistency of the API Ecosystem aligned with business.

All of below should be part of api-definition/deployment Secure by default for Internal Services/Clients for External Services/Clients Header enrichment + cleanup Mock versions from day-1 Help quickly play around ( until Prod ) Help QA Automation Level-3 REST ( HATEOS ) Support end-to-end persona that entity support via api Api-Gateway to also support Rate-Limits ( Local / Global ) Groups / Pages / Targets Custom Plugin scope JSON import/export base api deployment API based deployment on api

In addition to API quality and consistency, policies and contracts help with predictability. Your API consumers can evaluate whether they want to consume your API more effectively and have a better idea of what to expect when they do so.

You should place special emphasis in your documentation on how to authenticate with the API. It is critical to clearly detail the way in which you get whatever tokens or credentials required to authenticate, as well as how to present those when using the API. Authentication is often the first hurdle facing any developer intending to use your API, and in my experience, is often the biggest pain point. This is especially true if your API authentication is non-standard or has some proprietary peculiarity. If you are building a new API, strongly consider using an authentication scheme such as OAuth2.

OpenAPI / Swagger Mostly Auto generated from the code annotation JSON / YAML works Share working copy via Postman files with environment files, sample body payload per-populated, Postman files committed in the code repo.

There are many ways of doing this. Let me mention the most common ones, although it is possible to find other approaches. For syntactic validations, Spectral is king. Once you've defined your standards in the form of a ruleset, you can run a script that will give you where in your API there are ruleset violations so that you can correct them properly. For semantic validations, you can use GenAI integrated with Spectral to analyze the content of the fields and whether they make sense. Finally, you can use API Management Platforms to enforce runtime policies such as security, traffic shaping, throttling, and so on.

From my experience, effectively enforcing API policies and contracts often involves using an API gateway or service mesh like Kong or Apigee. These act as intermediaries, applying necessary policies such as rate limiting and authentication, and ensuring adherence to API contracts. Additionally, tools like Spectral for syntactic validations and GenAI for semantic checks have been invaluable. They pinpoint areas needing correction, ensuring your API meets defined standards. API Management Platforms are also crucial for runtime policy enforcement, managing security, and traffic. Each of these components plays a distinct role in creating a robust, policy-compliant API ecosystem.

For API docs on our team, we use tools like Swagger or Apigee that make the contract very clear. For enforcement, we use automatic testing tools like Postman or Pact to make sure the API follows the terms of its contract. In the API code, rules like rate limits and authentication are applied automatically. To set rate limits for certain paths, as an example, we could use middleware in Express.js.

API gateways act as the entry point for the API's and enforcing API policies and contracts at the entry level is key to secure and make API efficient.Many popular API Management tools come with so many OOTB policies which can be leveraged and enforced on the API's very easily.There are SDK's to build custom policies as well.API Management tools provide options to create contracts for different consumers and define SLA's if required.I have used Mulesoft's Anypoint platform which provided these features and is among the Gartner's Top pick for API Managment.

Especially when your API Ecosystem is huge automation is mandatory, otherwise, executing tests by hand will be expensive in time and resources. Tests should be run during the first stages of the API Lifecycle. The sooner the API fails, the better. As per toolsets, general-purpose tools can be found easily, such as Postman. There are also more vertical tools such as MockBank for Open Banking and Banking APIs.

The best way to monitor APIs is by using the API analytics bundled with the API Management/Integration platform you'll be using.

The API contracts being machine-readable are a huge advantage in regards to scanning for policy enforcing. Linting mechanisms could be leveraged to specify the list of rules and may be integrated as part of the continuous development cycle and used as a way to monitor the API specifications. Another benefit of this approach, beyond the automated monitoring of contracts, is the ability to generate, for documentation purposes, a catalog of rules based on the specified policies, serving as a single source of truth.

Monitoring API policies and contracts is crucial for ensuring the reliability, performance, and adherence to specified terms. Observability tools and platforms play a pivotal role in this process by providing insights into the behavior and usage of your APIs.

API Monitoring tool bundled with API Management tools provide valuable information on analyzing the usage and performance of API. Mulesoft's Monitoring tool provides insights on how many request were failed due to policy violation and from which geographic location it were targeted from. The monitoring tools play a key role in analyzing the effective ness of policies and contracts.

In order to record API policies and agreements comprehensively, it is important first to state and elaborate on rules of utilization, handling of data, authentication, and rate limits. Comprehensive documentations with examples can be done using Swagger/OpenAPI tools. Access controls, rate limiters, and standard error handling can be applied in enforcing policies. Automated as well as manual ways such as checking for compliance or simulating violations can be used in testing APIs. Logging, analytics and alerts are part of monitoring tools that help keep records on usage patterns thereby ensuring compliance with the laid down laws.

Documenting and enforcing API policies and contracts is crucial for maintaining consistency, security, and reliability in your API ecosystem. Few things that we diligently follow are : OpenAPI Specification: We use OpenAPI Specification to describe the API in a machine-readable format. This allows for automated generation of documentation, client libraries, and server stubs. Contract Definitions: We clearly define the contract between the client and the server. Versioning: We clearly define the API versioning strategy, and communicate how clients should handle version changes.

In addition to API design guidelines, industry standards such as ODATA or GraphQL, design languages to enforce contracts, or an inspection tool to verify endpoints - it is prudent to scrutinize the data contracts and protocols usage as well. Not everything needs to be an HTTP/S based REST or GraphQL endpoint. Inter-service communication, long running operations, large payload endpoints, or chatty endpoints may be better served with binary channels and persistent TCP connections. Some examples of this includes gRPC with protocol buffers or WCF service models with TCP binding carrying serializable binary objects.