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61. REST APIS

5 min read

API REVIEW

  • An API (Application Programming Interface) is a software interface that allows two applications to communicate with each other.
  • APIs are essential not just for network automation but for all kinds of applications
  • In SDN Architecture, APIs are use to communicate between apps and the SDN controller (via the NBI) and between the SDN controller and the network devices (via the SBI)
  • The NBI typically uses REST APIs
  • NETCONF and RESTCONF are popular Southbound APIs

CRUD OPERATIONS AND HTTP VERBS

  • CRUD ( CREATE, READ, UPDATE, DELETE) refers to the operations we perform using REST APIs

  • CREATE :

    • Used to CREATE new variables and set their initial values
      • Example: create a variable “ip_address” and set the value to “10.1.1.1”

  • READ :

    • Used to READ the value of a variable
      • Example: Read the value of variable “ip_address” (”10.1.1.1”)

  • UPDATE :

    • Used to CHANGE / UPDATE the value of a variable
      • Example: Change the value of “ip_address” from “10.1.1.1” to “10.2.3.4”

  • DELETE :

    • Used to DELETE variables
      • Example: Delete variable “ip_address”

  • HTTP uses verbs (aka. methods) that map to these CRUD operations

  • REST APIs typically use HTTP

HTTP REQUEST :

  • When an HTTP client sends a request to an HTTP server, the HTTP header includes information like this:
    • An HTTP Verb (ie: GET)
    • A URI (Uniform Resource Identifier) indicating the resource it is trying to access

An example of a URI (demonstrated later)

  • The HTTP request can include additional headers which pass additional information to the server.

Check the list at https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers

  • An example would be an ACCEPT header, which informs the server about the types(s) of data that can be sent back to the client.

    • Example: Accept: application/json or Accept: application/xml

  • You can also view standard HTTP header fields with some examples at https://en.wikipedia.org/wiki/List_of_HTTP_header_fields

  • When a REST client makes an API call (request) to a REST server, it will send an HTTP request like the one above

đź’ˇ REST APIs do NOT have to use HTTP for communication, although HTTP is the most common choice

HTTP RESPONSE :

  • The server’s response will include a STATUS CODE indicating if the request succeeded or failed, as well as other details
  • The FIRST digit indicates the class of the response:
    • 1xx : Informational - request was received, continuing process
    • 2xx : Successful - request was successfully received, understood, and accepted
    • 3xx : Redirection - further action needs to be taken in order to complete the request
    • 4xx : Client Error - request contains bad syntax or cannot be fulfilled
    • 5xx : Server Error - server failed to fulfill an apparently valid request

Examples of each HTTP Response class:

  • 1xx Informational

    • 102 Processing indicates that the server received the request and is processing it but the response is not available yet

  • 2xx Successful

    • 200 OK **indicates that the request succeeded
    • 201 Created indicates the request succeeded and a new resource was created

  • 3xx Redirection

    • 301 Moved Permanently indicates that the request resource has been moved and the server indicates its new location

  • 4xx Client Error

    • 403 Unauthorized means the client must authenticate to get a response
    • 404 Not Found means the requested resource was not found

  • 5xx Server Error

    • 500 Internal Server Error means the server encountered something unexpected that it doesn’t know how to handle

REST APIs

  • REST stands for Representational State Transfer

  • REST APIs are also know as REST-based APIs or RESTful APIs

    • REST isn’t a specific API. Instead it describes a set of rules about how the API should work

  • The SIX constraints of RESTful architecture are:

    • Stateless
    • Layered system
    • Uniform Interface
    • Client-Server
    • Cacheable or non-cacheable
    • Code-on-Demand (optional)

  • For applications to communicate over a network, networking protocols must be used to facilitate those communications

    • For REST APIs, HTTP(S) is the most common choice

REST: Client-Server

  • REST APIs use a client-server architecture
  • The client uses API calls (HTTP requests) to access the resources on the server
  • The separation between the client and server means they can both change and evolve independently of each other
    • When the client application changes or the server application changes, the interface between them must not break

REST: Stateless

  • REST APIs exchanges are STATELESS
  • This means that each API exchange is a separate event, independent of all past exchanges between the client and server
    • The server does not store information about previous requests from the client to determine how it should respond to new requests
  • If authentication is required, this means that the client must authenticate with the server for each request it makes
  • TCP is an example of a STATEFUL protocol
  • UDP is an example of STATELESS protocol

** Although REST APIs use HTTP, which uses TCP (STATEFUL) as it’s LAYER 4 protocol, HTTP and REST APIs themselves aren’t STATEFUL. The functions of each layer are separate !

REST: Cacheable or Non-Cacheable

  • REST APIs must support caching of data
  • Caching refers to storing data for future use
    • Example :
      • Your computer might cache many elements of a web page so it doesn’t have to retrieve the entire page every time you visit. This improves performance for the client and reduces load on the server
  • Not all resources have to be cacheable but cacheable resources MUST be declared as cacheable

FOR THE CCNA

REST API CALLS USING CISCO DEVNET

  • “Cisco DevNet is Cisco’s developer program to help developers and IT professionals who want to write applications and develop integrations with Cisco products, platforms, and API’s”

  • DevNet offers lots of free resources such as courses, tutorials, labs, sandboxes, documentation, etc to learn about AUTOMATION and develop your skills

  • There is also a DevNet certification track that you can pursue if you are interested in AUTOMATION

  • We will use their Cisco DNA Center Sandbox to send a REST API call using Postman

    • DNA Center is one of Cisco’s SDN Controllers (covered in more detail later)
    • Postman is a platform for building an using APIs

TO START:

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