DevOps Classroom notes 25/Oct/2025

Need for Rest API

HTTP

• HTTP Protocol runs over TCP
• HTTP Protocol needs a connection and it has
  • Request:
    • URL
    • Method/Verb
      • GET
      • PUT
      • POST
      • DELETE
      • HEAD
    • Headers
      • Key value pairs
    • Body
      • content
  • Response
    • Status code
      • 1xx (information)
      • 2xx (success)
      • 3xx (Redirection)
      • 4xx (client side errors)
      • 5xx (server side errors)
    • Headers
    • Body

Restful API

• A restful API is not a protocol, rather a practice or an approach recommended
• Restful APIs (Rest API or APIs) have principles

REST API Design Principles — Step by Step

---

Step 1: Client–Server Architecture

Principle: Separation of concerns
Description:
REST divides responsibilities — the client handles the user interface (UI/UX), while the server manages data and business logic. This allows both to evolve independently.
Example:
A web app (client) requests /api/doctors, and the server responds with JSON data.

---

Step 2: Statelessness

Principle: No session state on the server
Description:
Each client request must contain all necessary information for the server to process it. The server does not store session context between requests.
Example:
Every request includes an authentication token (e.g., JWT in headers).

---

Step 3: Cacheability

Principle: Enable caching where appropriate
Description:
Responses should specify whether they are cacheable to improve performance and scalability.
Example:
HTTP headers like Cache-Control: max-age=3600 tell clients how long they can cache a response.

---

Step 4: Uniform Interface

Principle: Consistent interaction between client and server
Description:
A uniform interface simplifies interaction and decouples clients from servers. REST achieves this through consistent conventions.
Example:
Use standard HTTP methods (GET, POST, PUT, DELETE) and well-defined resource URIs.

---

Step 5: Layered System

Principle: Use independent layers
Description:
REST systems can include multiple layers such as security, load balancing, and application servers. Each layer operates independently without needing full visibility into others.
Example:
A proxy or gateway handles authentication before forwarding requests to backend APIs.

---

Step 6: Code on Demand (Optional)

Principle: Extend client functionality dynamically
Description:
Servers can send executable code (like JavaScript) to clients to extend their behavior. This is optional and rarely used in modern APIs.
Example:
A server sends a JS snippet to be executed by the browser.

---

Step 7: Resource-Based (Noun-Oriented)

Principle: Focus on resources, not actions
Description:
REST APIs represent resources (nouns) rather than actions (verbs). HTTP methods define actions on these resources.
Example:
/api/patients/123 instead of /api/getPatient?id=123

Building Rest APIs in plain english

• Identify nouns & Verbs.
• Nouns become Resources, Verbs will be methods or sub resources
• Method:
  • GET: Retrive or select
  • PUT/PATCH: update
  • POST: create
  • DELETE: delete
• Endpoints:
  • A resource called as users
    • /api/v1/users
      • GET: Get all users
      • POST: Create a new user
    • /api/v1/users/1
      • GET: Get the user with id 1
      • PATCH/POST: Update the user info
      • DELETE: Delete the user
    • /api/v1/users/1/orders:
      • GET: Get all the orders of user with 1
      • POST: Create a order for user with id 1
• For using REST APIs, Documentations need to be published for this we have
  • OpenAPI spec
  • Swagger
• To test apis we use a tool called as postman

APIS

• We have two types on larger note
  • anonymous
  • authenticated
    • API Keys
    • Tokens

Consuming APIs from python

• Lets create a new project and add a dependency requests

import requests

BASE_URL = "https://petstore.swagger.io/v2"
PETS_URL = f"{BASE_URL}/pet"


def get_all_pets(status:str ='available'):
    PET_STATUS_URL = f"{PETS_URL}/findByStatus?status={status}"
    response = requests.get(
        PET_STATUS_URL,
        timeout=30)
    print(response)

    pets = response.json()
    for pet in pets:
        if 'id' in pet and 'name' in pet:
            print(f"{pet['id']} <==> {pet['name']}")
        else:
            print(pet)


if __name__ == "__main__":
    get_all_pets()

• Exercise: Create a simple python functions to use the product apis from here

Building Restful Apis using fastapi