Microservices vs Monolith in 2025: Lessons From Companies That Switched Back

The pendulum has swung. After a decade of "microservices everything," major companies are moving back to monoliths. Here's what we've learned.

Companies That Switched Back

Amazon Prime Video

The problem: Data passing between services via S3 and SQS added latency and cost that exceeded the monitoring service's budget.

Segment

Istio (Service Mesh)

The Real Cost of Microservices

When Microservices Make Sense

✅ Good Reasons to Use Microservices

❌ Bad Reasons to Use Microservices

The Modular Monolith: Best of Both Worlds

Traditional Monolith:        Modular Monolith:
┌──────────────────┐        ┌──────────────────┐
│   Everything     │        │  ┌────┐ ┌────┐   │
│   mixed          │        │  │Auth│ │Users│   │
│   together       │   →    │  └──┬─┘ └──┬─┘   │
│                  │        │  ┌──┴─┐ ┌──┴──┐  │
│   Spaghetti!     │        │  │API │ │Orders│  │
│                  │        │  └────┘ └─────┘  │
└──────────────────┘        └──────────────────┘
                             Clear boundaries,
                             single deployment

Implementation

my-app/
├── modules/
│   ├── auth/          # Self-contained module
│   │   ├── routes.ts
│   │   ├── service.ts
│   │   ├── repository.ts
│   │   └── types.ts
│   ├── users/
│   │   ├── routes.ts
│   │   ├── service.ts
│   │   └── ...
│   └── orders/
│       └── ...
├── shared/            # Shared utilities
│   ├── database.ts
│   └── middleware.ts
└── app.ts            # Composes modules

Decision Framework

Ask these questions before choosing:

The 2025 Consensus

Start with a modular monolith. Extract services only when you have a proven need. The complexity cost of premature microservices far exceeds the refactoring cost of splitting a well-structured monolith later.

Architecture should solve problems, not create them.