System Overview - Incremental migration plan
This system shows how to gradually move from a monolithic application to microservices. The goal is to keep the system working during migration, reduce risks, and improve scalability step-by-step.
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Incremental migration plan in Microservices - Architecture Diagram
Architecture Diagram
User | v Load Balancer | v API Gateway | +-------------------+-------------------+ | | | Monolith Service 1 Microservice A Microservice B | | | Database (Monolith) Database A Database B | | | Cache (Shared) Cache A Cache B
Components
User
client
End user sending requests
Load Balancer
load_balancer
Distributes incoming requests evenly to API Gateway instances
API Gateway
api_gateway
Routes requests to monolith or microservices based on migration status
Monolith Service 1
service
Original monolithic application handling some features
Microservice A
service
New microservice handling a migrated feature
Microservice B
service
Another new microservice handling another migrated feature
Database (Monolith)
database
Original monolith database storing legacy data
Database A
database
Database for Microservice A
Database B
database
Database for Microservice B
Cache (Shared)
cache
Shared cache used by monolith and microservices for fast data access
Cache A
cache
Cache dedicated to Microservice A
Cache B
cache
Cache dedicated to Microservice B
Request Flow - 12 Hops
User → Load Balancer
Load Balancer → API Gateway
API Gateway → Monolith Service 1
API Gateway → Microservice A
Microservice A → Cache A
Microservice A → Database A
Monolith Service 1 → Cache (Shared)
Monolith Service 1 → Database (Monolith)
Microservice B → Cache B
Microservice B → Database B
API Gateway → Load Balancer
Load Balancer → User
Failure Scenario
Component Fails:Database A
Impact:Microservice A cannot read or write data, causing feature unavailability. Cache may serve stale data but updates fail.
Mitigation:Use database replication and failover to standby database. Implement circuit breaker in microservice to degrade gracefully.
Architecture Quiz - 3 Questions
Test your understanding
Which component decides whether to send a request to the monolith or a microservice?
Design Principle
This architecture shows how to migrate a monolith to microservices step-by-step by routing requests through an API Gateway. It uses caching to reduce database load and isolates databases per microservice to improve scalability and fault tolerance.