RESTful Web API Design

An API is a set of routines or functions. It’s an interface used for performing tasks, retrieving data, and manipulating data. APIs use HTTP methods, which are used on a resource to GET, POST (submit form data), PUT (for updating files), PATCH (a partial update), and DELETE.

Adding an API

  • Bolt-on strategy – when you already have an application and are adding an API to it
  • Greenfield strategy – no underlining application. There’s complete freedom and flexibility to do what you want. Generally the “API first” or “mobile first” mentality.
  • Facade strategy – wraps existing logic with replace as you go. This is ideal for legacy systems so the application is always functional.

Designing the Relationship

  • Independent – the resources may exist regardless of the other existing but they may reference each other
  • Dependent – one resource cannot exist without the parent
  • Associative – they are independent of each other but the relationship contains additional properties to describe it

Planning the Relationships

  • Ask yourself the following questions:
    • Can both resources exist without the other?
    • Does one resource only exist when the other exists?
    • Does the relationship between resources require more information than just the links between them?
  • It should be relatively easy to map out the flow, action, etc for each resource. If not, you need to revise your design.
  • Consider using notecards to write down each resource action


  • REST stands for Representational State Transfer
  • It’s an architecture for designing network-based applications
  • It is not a protocol, framework, or standard

Benefits of Stateless Servers

  • Visibility – monitoring systems and developers do not need to look beyond the request to trace a bug
  • Reliability – easy to recover from system failures

Drawbacks of Stateless Servers

  • Network Bandwidth – client sends state for every request
  • Complexity – all clients must handle their states

Benefits of Caching

  • Performance – for stateless and caching, many requests do not need to go all the way to the server
  • Scalability – server gets fewer requests so it can handle more clients

Drawbacks of Caching

  • Data reliability – clients might use stale data

Facets of a Uniform Interface

  • Self descriptive messages
  • Server includes metadata, such as Content-Type, to help clients process the responses
  • Hypermedia as the engine of application state (HATEOAS)
  • Client only assumes a fixed entry-point to the API, the server tells clients all other available actions through hyperlinksBenefits of a Layered System
  • Encapsulation (simplify an interface to a legacy server)
  • Scalability (layers enable load balancing)
  • Security (add access control rules to data crossing a boundary, just like a firewall)

Drawbacks of a Layered System

  • Latency – adding layers increases latency

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