Payment handling in LLD - Architecture Diagram

System Overview - Payment handling

This system securely processes user payments for online purchases. It handles payment requests, validates them, communicates with external payment gateways, and updates order status. Key requirements include security, reliability, and fast response times.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Payment Service <--> Cache
  |
  v
Database
  |
  v
External Payment Gateway

Components

User

client

Initiates payment requests

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Handles authentication, routing, and request validation

Payment Service

service

Processes payment logic, communicates with database and external gateway

Cache

cache

Stores recent payment status and reduces database load

Database

database

Stores payment records and order status

External Payment Gateway

external_service

Processes actual payment transactions with banks or card networks

Request Flow - 12 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Payment Service

Payment Service → Cache

Cache → Payment Service

Payment Service → Database

Payment Service → External Payment Gateway

External Payment Gateway → Payment Service

Payment Service → Cache

Payment Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Database

Impact:New payment records cannot be saved; payment status updates fail. Cached payment status can still be served for recent queries.

Mitigation:Use database replication and failover to a standby database. Cache serves read requests temporarily. Alert system triggers for manual intervention.

Architecture Quiz - 3 Questions

Which component first handles user payment requests after they pass through the Load Balancer?

A API Gateway

B Payment Service

C Cache

D Database

Design Principle

This architecture uses layered components to separate concerns: Load Balancer for traffic distribution, API Gateway for security and routing, Payment Service for business logic, Cache for performance, Database for persistence, and External Gateway for actual payment processing. This separation improves scalability, reliability, and maintainability.