Why database choice impacts architecture in HLD - Architecture Impact

System Overview - Why database choice impacts architecture

This system demonstrates how choosing different types of databases affects the overall architecture of an application. Key requirements include handling data storage efficiently, supporting scalability, and ensuring data consistency based on the database type.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +--------------------+--------------------+
  |                    |                    |
Relational DB Service  NoSQL DB Service    Cache
  |                    |                    |
Relational DB         NoSQL DB             Redis

Components

User

client

Initiates requests to the system

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Routes requests to appropriate backend services based on database choice

Relational DB Service

service

Handles requests that require relational database operations

NoSQL DB Service

service

Handles requests that require NoSQL database operations

Cache

cache

Stores frequently accessed data to reduce database load

Relational DB

database

Stores structured data with strong consistency and supports complex queries

NoSQL DB

database

Stores flexible schema data optimized for scalability and high throughput

Redis

cache

In-memory cache for fast data retrieval

Request Flow - 16 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Cache

Cache → API Gateway

API Gateway → Relational DB Service

Relational DB Service → Relational DB

Relational DB → Relational DB Service

Relational DB Service → Cache

Relational DB Service → API Gateway

API Gateway → NoSQL DB Service

NoSQL DB Service → NoSQL DB

NoSQL DB → NoSQL DB Service

NoSQL DB Service → Cache

NoSQL DB Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Relational DB

Impact:Relational DB Service cannot retrieve or store data, causing failures for requests needing relational data. Cache may serve stale data but writes fail.

Mitigation:Use database replication and failover to standby relational DB instances. Cache serves read requests temporarily. API Gateway can route requests to NoSQL DB Service if applicable.

Architecture Quiz - 3 Questions

Why does the API Gateway route requests differently based on database choice?

A Because different databases require different query languages and data handling

B Because the API Gateway stores all data itself

C Because users connect directly to databases

D Because caches replace databases entirely

Design Principle

Choosing a database type affects how the system routes requests, manages data consistency, and scales. Relational databases require structured queries and strong consistency, while NoSQL databases offer flexible schemas and scalability. Caches improve performance by reducing database load. The architecture must adapt to these differences to meet system requirements.