Why gradual migration reduces risk in Microservices - Architecture Impact

System Overview - Why gradual migration reduces risk

This system shows how a gradual migration from a monolithic application to microservices reduces risk. Instead of switching all at once, parts of the system are moved step-by-step. This allows testing and fixing issues in small pieces, avoiding big failures.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +---------------------+
  |                     |
Monolith Service    New Microservice
  |                     |
Database (Shared)   Database (New)
  |
Cache

Components

User

user

End user who sends requests to the system

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Routes requests to either the monolith or new microservice based on migration progress

Monolith Service

service

Original application handling most requests before migration

New Microservice

service

Newly developed microservice handling migrated features

Database (Shared)

database

Database used by the monolith and partially by microservices during migration

Database (New)

database

New database dedicated to the microservice for isolated data management

Cache

cache

Speeds up data retrieval for both monolith and microservices

Request Flow - 10 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Monolith Service or New Microservice

Monolith Service or New Microservice → Cache

Cache → Monolith Service or New Microservice

Monolith Service or New Microservice → Database (Shared or New)

Database (Shared or New) → Monolith Service or New Microservice

Monolith Service or New Microservice → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:New Microservice

Impact:Requests routed to the new microservice fail, causing partial service disruption for migrated features.

Mitigation:API Gateway routes affected requests back to the monolith service as a fallback until the microservice is fixed.

Architecture Quiz - 3 Questions

Why does the API Gateway route some requests to the monolith and others to the new microservice?

A Because the monolith is faster than microservices

B To balance load evenly between services

C To gradually migrate features and reduce risk

D To avoid using the cache

Design Principle

Gradual migration reduces risk by allowing parts of the system to be moved step-by-step. This approach enables testing, monitoring, and rollback of small changes without disrupting the entire system, improving stability and reliability during transition.