HLDsystem_design~12 mins

Payment integration architecture in HLD - Architecture Diagram

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System Overview - Payment integration architecture

This system handles online payment processing for an e-commerce platform. It securely accepts payment requests from users, communicates with external payment gateways, and updates order status upon successful transactions. Key requirements include security, reliability, and scalability to handle many simultaneous payments.

Architecture Diagram

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

Components

User

client

Initiates payment requests via web or mobile app

Load Balancer

load_balancer

Distributes incoming payment requests evenly across API Gateway instances

API Gateway

api_gateway

Handles authentication, routing, and rate limiting for payment requests

Payment Service

service

Processes payment logic, interacts with cache, database, and message queue

Cache

cache

Stores recent payment session data to reduce database load

Database

database

Stores persistent payment and order records

Message Queue

queue

Queues payment confirmation messages for asynchronous processing

External Payment Gateway

external_service

Third-party service that processes actual payment transactions

Request Flow - 13 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Payment Service

Payment Service → Cache

Cache → Payment Service

Payment Service → Database

Payment Service → Message Queue

Message Queue → External Payment Gateway

External Payment Gateway → Message Queue

Message Queue → Payment Service

Payment Service → Cache

Payment Service → API Gateway

API Gateway → User

Failure Scenario

Component Fails:Database

Impact:New payment records cannot be saved; payment status updates fail. Cached data may be stale.

Mitigation:Reads can still be served from cache; writes are retried or queued. Database replication and failover reduce downtime.

Architecture Quiz - 3 Questions

Test your understanding

Which component first handles the user's payment request after it passes through the Load Balancer?

APayment Service

BAPI Gateway

CCache

DDatabase

Design Principle

This architecture uses layered components to ensure secure, scalable payment processing. Caching reduces database load, asynchronous messaging decouples external payment processing, and load balancing ensures availability under high traffic.