Database replication (master-slave) in HLD - Architecture Diagram

System Overview - Database replication (master-slave)

This system uses a master-slave database replication setup to improve data availability and read scalability. The master database handles all write operations, while one or more slave databases replicate data from the master and serve read requests.

Key requirements include data consistency from master to slaves, load distribution for reads, and failover handling if the master fails.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +-------------------+
  |                   |
Master DB <---------> Slave DB(s)
  |                   |
  +-------------------+

Components

User

client

Initiates requests to the system

Load Balancer

load_balancer

Distributes incoming requests to API Gateway instances

API Gateway

api_gateway

Routes requests to appropriate services and manages traffic

Master DB

database_master

Handles all write operations and replicates data to slaves

Slave DB(s)

database_slave

Replicates data from master and handles read requests

Request Flow - 8 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Master DB

Master DB → Slave DB(s)

API Gateway → Slave DB(s)

Slave DB(s) → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Master DB

Impact:Write operations fail; slaves continue serving stale read data

Mitigation:Promote a slave to master using failover process; update API Gateway routing

Architecture Quiz - 3 Questions

Which component handles all write operations in this system?

A Load Balancer

B Master DB

C Slave DB

D API Gateway

Design Principle

This architecture separates write and read workloads by using a master database for writes and slave databases for reads. It improves read scalability and availability while maintaining data consistency through asynchronous replication.