Representational State Transfer APIs are also known as REST-based APIs or RESTful APIs

• REST isn't a specific API; it describes a set of rules about how the API should work

There are 6 constraints of RESTful architecture

• Uniform Interface
• Client-Server
  • Client uses API calls (like HTTP Requests) to access resources on the server
  • Separation between the client and server means they can change independently
    • When the client application changes or the server application changes, the interface between them must not break
• Stateless
  • Each API exchange is a separate event, independent of all past exchanges between client and server
    • The server does not store information from previous requests to determine how it should respond to new requests
    • e.g., the client must authenticate with each request
  • Although REST APIs use HTTP, which uses TCP as its L4 protocol, HTTP and REST APIs themselves aren't stateful
    • The functions of each layer are separate
• Cacheable or non-cacheable
  • Must support caching of data
    • However, not all resources must be cacheable
  • Cacheable resources must bee marked as cacheable
• Layered system
• Code-on-demand (optional)

Rest APIs are used in SDN Northbound APIs between the Control Layer and the Application Layer, allowing devices in those layers to communicate