Why We Replaced Microservices with a Modular Monolith in Next.js 15

In early 2024, our engineering team found ourselves spending more time managing gRPC schemas, internal Docker networks, and Kubernetes service meshes than writing customer-facing logic.

Here is the data, testing telemetry, and architectural rationale that drove our decision to consolidate four distributed microservices back into a high-performance modular monolith built on Next.js 15 App Router.

The Microservice Tax

When teams adopt microservices prematurely, they swap code-level complexity for operational and network complexity:

1. Network Hops & Latency: An internal checkout flow required 5 inter-service HTTP calls, adding 120ms of artificial latency.
2. Distributed Transaction Failures: Two-phase commits across distinct databases were fragile and prone to partial failure.
3. Developer Velocity Collapse: Local development required running 7 Docker containers and seeding 3 separate databases.

The Modular Monolith Alternative

With Next.js 15, React Server Components (RSC), and TypeScript project references, we achieved strict domain boundaries without running independent servers:

• Colocated Server Actions: Zero HTTP serialization overhead for internal domain calls.
• Single Database with Schemas: Logical isolation inside PostgreSQL via schemas (auth, billing, catalog) without the nightmare of distributed joins.
• Instant Local DX: npm run dev starts in under 2 seconds.