Scalable Modular Monolith Architecture for Modern Apps

In modern software development, teams often face a critical decision: Should we opt for a monolith or microservices architecture? This decision should be based on the specific needs of your project. For instance, if you’re building a small, simple application, a monolith might be the best choice. However, if you’re working on an extensive, complex system with multiple teams, microservices could be the way to go. While microservices bring scalability and independence, they also introduce complexity in deployment, communication, and monitoring. On the other hand, a traditional monolith is simpler but becomes harder to maintain as the application grows.

That’s where the modular monolith comes in—a balanced approach that addresses the challenges of both monoliths and microservices, offering a way forward that is both scalable and manageable.

What Exactly Is a Modular Monolith?

A Modular Monolith is a software design where the application is deployed as a single unit but internally organized into independent, well-encapsulated modules.

• One deployable unit
• Feature-based modular design
• Easier to test, maintain, and scale
• Prepares the ground for future micro-services

Think of it as ‘build like microservices, deploy like a monolith.’ This means you can develop your application in a modular, independent manner, similar to how you would with microservices. However, when it comes to deployment, you can treat the application as a single unit, like a monolith.

Monolith vs Modular Monolith

Key Benefits of a Modular Monolith

A modular monolith offers the perfect balance between simplicity and scalability. Here are the most significant advantages:

• Simplified Deployment—Unlike microservices that require complex deployment pipelines, a modular monolith can be deployed as a single unit, reducing errors and streamlining releases.
• Improved Performance—Communication between modules happens in-process, eliminating network latency and serialization overhead for faster and more reliable execution.
• Increased Development Velocity—A unified codebase simplifies debugging, testing, and collaboration, enabling teams to deliver features more efficiently.
• Simplified Transaction Management—Since modules can share the same database, handling transactions becomes more straightforward compared to the complexities of distributed systems.
• Reduced Operational Complexity—Fewer moving parts mean lower infrastructure overhead, easier maintenance, and a more stable environment.
• Smooth Transition to Microservices – A well-structured, modular monolith enables a gradual, controlled migration to microservices when scaling demands it, thereby avoiding the need for a complete architectural overhaul.

This approach provides a scalable, high-performing foundation that supports current needs while offering flexibility for future growth.

Designing an E-Commerce App Using Modular Monolithic Architecture

In a traditional monolithic architecture, implementing vertical use cases—like listing products, adding items to a basket, or checking out orders—often requires touching multiple layers of the application. This can make development, maintenance, and scaling more challenging.

Example: E-Commerce Application

In our e-commerce application, we have structured the system into three modules:

Each module contains everything it needs to function independently, from data storage to business logic. Despite this modularisation, the entire application still runs as a single deployment unit, retaining the simplicity of a monolithic system.

Communication Between Modules

Modules inside a modular monolith can communicate in different ways:

Function Calls or MediatR—simple, in-process communication

Message Brokers (Kafka, RabbitMQ) – decoupled, event-driven communication

gRPC—high-performance RPC framework with strongly typed contracts

Why gRPC?

gRPC provides:

• High performance via HTTP/2
• Strongly typed contracts with Protocol Buffers
• Cross-language support (C#, Java, Go, Python, etc.)
• Efficient communication with small payloads
• Streaming support (unary, client, server, bi-directional)
• Code generation for clients & servers

This makes gRPC an excellent choice for modular monoliths and microservices.

Project Overview

A sample modular monolith, designed for flexibility and adaptability, could look like this:

– Host (API) → The central deployment unit

– Booking Module → Handles customer bookings

– Order Module Handles order creation & management

– User Module → Manages authentication and user operations

– Shared Module → Common logic like gRPC protos, authentication services, constants, etc.

Modules communicate via gRPC, a high-performance, open-source universal RPC framework, and are registered in the host project for deployment.

What’s Next in Modular Monolith

At Zobi Web Solutions, we believe the Modular Monolith is a powerful foundation for teams that want the clarity of modular design without the operational complexity of microservices.

With this approach, you can:

• Build applications that are scalable, testable, and maintainable
• Keep deployment streamlined and hassle-free
• Lay a solid groundwork for an easy transition to microservices whenever the time is right
  

In short: Start modular, and evolve into microservices only when it truly adds value—a philosophy we champion at Zobi Web Solutions to help our clients grow with confidence and efficiency.

The story doesn’t end here—more chapters on building better modular monoliths are coming soon.