Design a Large-Scale System Migration
Design a strategy to migrate a monolithic system serving 10M users to microservices with zero downtime.
Use Strangler Fig pattern, implement feature flags, parallel running, and gradual traffic shifting.
How do you maintain feature velocity during migration?
Consider data consistency challenges
Think about team capacity and skills
3 migration
Extract services incrementally
2 foundation
Build platform, CI/CD, observability
1 preparation
Inventory, documentation, team training
4 optimization
Decommission legacy, optimize new system
Large-scale migrations require careful planning, risk mitigation, and organizational alignment.
cutover
Final sync window, minimize duration
strategies
- •Dual-write
- •CDC (Change Data Capture)
- •Batch + catch-up
consistency
Verify data integrity at each step
feature flags
Control rollout percentage per feature
rollback plan
Every change must be reversible
circuit breakers
Automatic fallback to old system
parallel running
Run old and new systems, compare results
business
- •Feature velocity
- •Incident rate
- •Developer satisfaction
technical
- •Error rate comparison
- •Latency comparison
- •Resource utilization
strangler fig
steps
- •Identify bounded contexts
- •Build new service
- •Route traffic gradually
- •Decommission old code
description
Incrementally replace parts of the system
branch by abstraction
use case
Database migrations, library replacements
description
Create abstraction layer, swap implementations
timeline
Be realistic, plan for unknowns
communication
Regular updates to stakeholders, clear milestones
team structure
Dedicated migration team or distributed ownership