Software architecture trends often swing like a pendulum. Over the past decade, microservices dominated the conversation, promising scalability, autonomy, and faster delivery. Today, many teams are re-evaluating that choice and rediscovering a more balanced approach: the modular monolith.
This article explores why microservices became the default, where they struggled, and why modular monolithic architecture is emerging as a pragmatic alternative for many teams.
TL;DR: Modular Monolith vs Microservices
Microservices can enable independent scaling and deployments, but they also introduce distributed-system complexity that many teams don’t need. A modular monolith is often a better fit for small to medium teams because it keeps strong domain boundaries inside a single deployable application.
- Microservices work best for large organizations with high operational maturity and autonomous teams.
- Modular monolith architecture provides clear module boundaries without network calls between domains.
- If your main challenge is delivery speed, maintainability, and cost, a modular monolith is often the pragmatic default.
- You can still evolve: well-designed modules can be extracted into microservices later if scale demands it.
Who This Article Is For
This guide is designed for software teams and engineering leaders who are evaluating modern application architecture and want to avoid unnecessary complexity.
- Startup and SaaS teams deciding between microservices and monolithic architectures
- Small to medium engineering teams struggling with microservices operational overhead
- Technical leads planning long-term scalable system design
- Organizations considering a transition from microservices back to a modular monolith
- Developers looking for a practical, maintainable architecture approach
Why Microservices Became the Default Choice
For nearly a decade, microservices were seen as the natural evolution of software architecture. As systems grew and teams expanded, breaking applications into smaller services promised independent deployments, better scalability, and faster delivery.
Microservices also became a signal of technical maturity. Organizations associated them with industry leaders and modern engineering practices, often adopting them early to avoid future rework.
For a time, this approach appeared inevitable. Splitting systems felt like progress.
Common Myths About Microservices
Microservices are often presented as a universal solution for modern software systems. In reality, many assumptions around them are misleading.
-
Myth: Microservices automatically improve scalability.
In practice, many applications scale uniformly, meaning the entire system grows together. Microservices only provide real benefits when different components have significantly different scaling requirements. -
Myth: Microservices speed up development for all teams.
While they can help large autonomous teams, smaller teams often experience slower delivery due to increased coordination, infrastructure setup, and deployment pipelines. -
Myth: Monoliths are inherently outdated.
A well-structured modular monolith follows modern design principles and can be just as maintainable and scalable as distributed systems - without unnecessary complexity. -
Myth: You must start with microservices to scale later.
Starting with a modular monolith often provides a cleaner and safer path to microservices when real scaling needs emerge.
Why Microservices Struggle Outside Their Intended Context?
Microservices were designed for a very specific environment: large systems, autonomous teams, and high operational maturity.
Most teams, however, do not operate under these conditions.
In practice, microservices shifted complexity away from code and into infrastructure. Simple changes began to require coordination across multiple services, pipelines, and teams. Deployments slowed, debugging became distributed, and observability turned into a requirement rather than a nice-to-have. Infrastructure costs increased even when scale did not.
Microservices didn't fail as an idea. They struggle when applied outside the context they were designed for creating unnecessary complexity without delivering their intended benefits.
A Real-World Scenario: When Microservices Became a Bottleneck
Consider a growing SaaS product with a small engineering team of six developers. To follow modern best practices, the team adopted a microservices architecture early in the product lifecycle.
Within a year, the system consisted of more than ten services, each with its own deployment pipeline, monitoring setup, and infrastructure configuration. Simple feature changes required updates across multiple services and coordination between developers.
Instead of moving faster, the team spent increasing time managing CI/CD pipelines, debugging distributed failures, and maintaining cloud resources. Infrastructure costs rose, while feature delivery slowed.
After consolidating the system into a modular monolith with clearly defined internal modules, the team reduced operational overhead, simplified deployments, and improved development speed - while still maintaining strong domain separation.
This pattern is increasingly common across startups and small to medium engineering teams.
What is a Modular Monolith?
A modular monolith structures a single application as a collection of internally isolated modules, each aligned with a specific business or functional domain. Instead of allowing unrestricted access across the codebase, modules interact only through explicit contracts, ensuring that related functionality stays together and unrelated concerns remain separated. This intentional structure reduces accidental coupling and leads to a system that is more cohesive, predictable, and resilient to change.
Key Characteristics of a Modular Monolith
A modular monolith is defined not just by its structure, but by the architectural rules it enforces.
- Single runtime and deployment unit
- Internally isolated, domain-aligned modules
- Explicit APIs between modules
- No direct data access across module boundaries - modules access other modules' data only through explicit APIs, never directly querying each other's tables
- No network calls between domains
- Clear ownership and responsibility per module
These characteristics provide service-like boundaries while keeping execution in-process.
Architecture Comparison
| Aspect | Monolith | Modular Monolith | Microservices |
|---|---|---|---|
| Structure | Tightly coupled codebase | Single codebase with strict modules | Multiple independent services |
| Deployment | Single | Single | Multiple |
| Communication | In-process | In-process via module APIs | Network calls |
| Data ownership | Shared database, no boundaries | Single database, logical boundaries per module | Database per service |
| CI/CD complexity | Low | Low | High |
| Operational overhead | Low | Low–Medium | Very high |
| Debugging | Simple early | Predictable | Complex (distributed) |
| Scalability | Whole app (vertical/horizontal) | Whole app (vertical/horizontal) | Independent per service |
| Best fit for | Very small teams | Small–medium teams | Large organizations |
Benefits of Modular Monolithic Architecture
When implemented correctly, modular monolithic architecture offers practical advantages across development, operations, and cost.
- Strong modular boundaries: Clear separation of domains prevents tight coupling while keeping related logic together.
- ACID transactions across modules: Cross-module operations can use native database transactions, avoiding the complexity of distributed transaction patterns like sagas or two-phase commit required in microservices.
- Simple deployment and operations: Single build, deploy, and rollback without distributed-system overhead.
- Lower complexity, easier debugging: In-process communication enables predictable behavior and straightforward troubleshooting.
- Faster development and CI/CD: Fewer pipelines and dependencies improve delivery speed and reliability.
- Future-ready architecture: Well-defined modules can be extracted into microservices when scale or team size demands it.
Challenges of Modular Monolithic Architecture
Despite its advantages, a modular monolith is not without trade-offs.
- Requires strong discipline: Without strict enforcement of module boundaries, it can degrade into a tightly coupled system.
- Limited independent scalability: The entire application scales as a unit, though horizontal scaling across multiple instances is fully supported.
- Shared deployment risk: A bug in one module can impact the whole system.
- Growing codebase over time: Can become harder to navigate without structure.
- Boundary enforcement needs tooling: Requires architectural rules and automated checks.
When to Use Modular Monolithic Architecture
Modular monolithic architecture is most effective in the following scenarios.
- Small to medium-sized teams: Need simplicity with domain separation.
- Early to mid-stage products: Flexibility matters more than fine-grained scalability.
- Limited operational maturity: Avoid distributed overhead.
- Uniform scaling needs: Most components scale together.
- Systems expected to evolve: Clean path to microservices later.
Frequently Asked Questions (FAQ)
Is a modular monolith better than microservices?
A modular monolith is often better for small to medium-sized teams because it reduces operational complexity while maintaining strong architectural boundaries. Microservices are more suitable for large organizations with high scalability and operational maturity.
Can a modular monolith scale?
Yes. A modular monolith can scale effectively by scaling the entire application. In many real-world systems, most components scale together, making this approach sufficient and simpler than distributed microservices.
When should you choose microservices?
Microservices make sense when different parts of the system require independent scaling, when teams are large and autonomous, and when the organization can handle distributed system complexity.
Is starting with a monolith a bad practice?
No. Starting with a well-structured modular monolith is considered a best practice by many experienced architects. It provides simplicity early on and allows clean evolution into microservices when needed.
How is a modular monolith different from a traditional monolith?
A traditional monolith often lacks clear boundaries and becomes tightly coupled over time. A modular monolith enforces strict module separation, explicit APIs, and domain ownership while remaining a single deployable application.
Final Thoughts
Microservices are not obsolete - but they are no longer the default answer for every system.
For many teams, the real challenge is not scale. It is clarity, ownership, and operational simplicity.
Modular monolithic architecture offers a pragmatic middle ground: strong internal boundaries without unnecessary distributed system complexity.
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