Backend Fundamentals
1 What is Backend?
Backend refers to the server-side part of an application that handles business logic, data processing, authentication, database interactions and serves data to the client. It runs on a server and is not directly visible to users.
2) High Level Architecture
- Building the backbone of modern applications
Key Responsibilities:
• Handle client requests
• Business logic & processing
Interact with databases
Authentication & authorization
File storage, caching, background jobs Ensure security, scalability & reliability
Client
DNS
Load Balancer
Backend Server
Request
(Browser/
Mobile App)
000
Response
(resolves domain to IP)
(distributes traffic)
(API, Business Logic)
Example:
Database/ Cache / External Cache / External Services
3) Request - Response Lifecycle
1 Client sends a request (e.g. GET /api/users)
(2 DNS resolves the domain to an IP address
3 Request reaches the load balancer (if any)
4 Routed to a backend server (application server)
5 Server processes the request (business logic, DB calls etc.)
6 Response is sent back to the client (usually in JSON)
4) Stateless vs Stateful
5
Stateless
Each request is independent
• No client data is stored on server
Easier to scale (horizontal scaling)
Examples: REST APIS, most modern
web apps
Stateful
Server maintains client state
GET /api/users/1
Client sends HTTP request
2) Server fetches user from DB
3) Returns response
Subsequent requests depend on previous ones
Harder to scale
Examples: Traditional sessions, some real-time apps (e.g. WebSockets)
Common Backend Technologies
Languages: Java, Python, Node.js, Go, C#, Ruby, PHP
• Frameworks: Spring Boot, Express.js, Django, FastAPI, .NET
Databases: MySQL, PostgreSQL, MongoDB, Redis
• Other Tools: Docker, Kubernetes, Nginx, Kafka, RabbitMQ
"name": "Abhishek"
"email": "abhi@examp
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Interview Point:
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Why are stateless services
preferred?
Easy to scale
More reliable
→ Works well with loaders
→ No server-side session storage
280
data
Key Takeaways:
Backend handles business logic and
Follows request-response model
Stateless design helps in scaling
Uses databases, caches and external services
•Focus on security, performance and
