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From Legacy Monolith to Microservices: A Real Case Study

When a monolithic app failed at 3,000 concurrent users, we had two options: full rewrite or strategic extraction. Here's what we chose and why.

UppLabs TeamDecember 27, 202410 min read
From Legacy Monolith to Microservices: A Real Case Study

68% of companies are already using microservices in production, and teams that have migrated report a 13x increase in release frequency. But the migration path from monolith to microservices is where most companies stumble.

Monolith vs. Microservices: The Real Trade-offs

Monolith Advantages

  • Immediate business logic implementation — ship features fast
  • Simpler end-to-end testing — one deployment unit
  • Straightforward deployment and scaling for small teams
  • Most economical option when you're validating product-market fit

Monolith Pain Points

  • Development slows as codebase grows
  • Can't scale individual components independently
  • One bug can crash the entire application
  • Code quality deteriorates as team size increases

The Real Case Study

Our client's application was failing at 3,000+ concurrent users. The root causes: monolithic architecture with no separation of concerns, unoptimized backend, database triggers as performance bottlenecks, and business logic scattered across triggers, stored procedures, and C# code.

We presented two options:

  • Option 1: Complete rewrite to microservices — 12+ months, 5+ developers, high risk
  • Option 2: Extract a single high-impact microservice — 2 months, 2 developers, low risk

The client chose Option 2. We built a Public Gateway API that enabled communication between the legacy monolith and the new microservice. This "strangler fig" approach let us extract the most performance-critical component without disrupting the entire system.

The Lesson

You don't need to rewrite everything at once. Start with the component that causes the most pain, extract it into a service, and build a communication layer between old and new. Repeat. It's slower than a big-bang rewrite on paper, but it's dramatically safer — and in practice, usually faster too.

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