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Monolith vs
Microservices

The most debated topic in engineering. Startups rush to microservices and die. Giants cling to monoliths and stagnate. Where is the balance?

Definitions

Monolith

📦

A single deployable unit. All code (Auth, Orders, Payments) runs in the same process, sharing the same memory and database.

Microservices

🔑
🛒
💳

Small, independent services communicating over a network (HTTP/gRPC). Each has its own database and can be deployed separately.

In Defense of the Monolith

shield

Why you should probably start here

  • 1. Simple Deployment:One repo, one CI pipeline, one Docker container.
  • 2. Atomic Transactions:BEGIN... COMMIT works. No distributed sagas needed.
  • 3. Zero Network Latency:Function calls are nanoseconds. RPC calls are milliseconds.
  • 4. Easier Refactoring:Moving code between modules is just copy-paste. No breaking API contracts between teams.
"Don't start with microservices. Start with a modular monolith." — Martin Fowler

Microservices Reality Check

Microservices solve organizational problems, not technical ones. They allow 500 engineers to work without stepping on toes. But the cost is high.

The Hidden Costs

  • Distributed Tracing: Debugging a request across 10 services is a nightmare.
  • Eventual Consistency: Data is never consistent everywhere at once.
  • Network Failure: What if the Payment service is down?
  • DevOps Tax: You need K8s, Service Mesh, specialized infra teams.

"If you can't build a well-structured monolith, what makes you think you can build well-structured microservices?"

— Simon Brown

When to Split

The Checklist

Team SizeIs the team too big (> 100)? Are merge conflicts blocking deployment?
Valid Reason
Independent ScalingDoes 'Image Processing' need 100 CPUs while 'User Profile' needs 1?
Valid Reason
Fault IsolationIf 'Recommendations' crash, 'Checkout' must stay up.
Valid Reason
Tech Stack DiversityWe want to write the ML service in Python, but the app is in Java.
Valid Reason
Resume Driven DevelopmentThe CTO wants to use Kubernetes because it's cool.
BAD REASON

Migration: The Strangler Fig

How do you move from Monolith to Microservices? Never rewrite from scratch.

Phase 1

Put a Load Balancer / API Gateway in front of the Monolith.

Phase 2

Identify ONE bounded context (e.g., Billing). Build a new Service for it.

Phase 3

Route /billing/* to the new service. Everything else still goes to Monolith.

Repeat until the Monolith is empty (or small enough to be just another service).