Firstly, I would use the RESTful architecture as a starting point since it is well-known, easy to understand, and promotes good separation of concerns. Additionally, I would ensure that the API is versioned, so that changes can be made without breaking existing clients.
In terms of scalability, I would focus on statelessness to allow for easy horizontal scaling. This means that each request should be self-contained and not depend on any previous state. I would also implement caching strategies to reduce the load on the backend services, and consider rate limiting to prevent abuse.
For maintainability, I would emphasize clear and concise documentation that is kept up-to-date. This helps both internal developers and external consumers of the API understand its usage and expected behavior. Additionally, I would advocate for modular code organization and a consistent naming convention to make it easier to navigate and maintain the codebase.
One challenge I recently encountered was designing an API for a system with many interconnected resources. To address this, I used the HATEOAS (Hypermedia as the Engine of Application State) principle, which involves embedding links within the API responses to guide clients through the available actions and resources.
Overall, the key to designing a scalable and maintainable API lies in embracing best practices, keeping the codebase organized, and continuously iterating and refining the design as the application evolves.