Microservices Antipattern: The Distributed Monolith 🛠️
We’re diving deep into an important concept called the “Distributed Monolith” — an antipattern that can sneak into our microservices architecture if we’re not careful. 📉
While microservices promise flexibility, scalability, and independent deployments, the distributed monolith retains many of the drawbacks of a monolithic architecture, despite being broken down into separate services. Let’s explore what a distributed monolith is, why it happens, its impacts, and how to avoid it.
What is a Distributed Monolith? 🤔
A distributed monolith is an antipattern where a supposedly microservices-based system retains the drawbacks of a monolithic architecture. Despite being broken down into separate services, these services are tightly coupled and interdependent, resulting in a system that is difficult to scale, deploy, and maintain.
Here’s what typically characterizes a distributed monolith:
Tight Coupling Across Services:
- Services are highly dependent on each other. Changes in one service often require changes in others, making independent deployments nearly impossible. This tight coupling slows down development and increases the risk of bugs.
Synchronized Deployments:
- Due to interdependencies, all services need to be deployed together. This negates one of the main benefits of microservices, which is the ability to deploy independently.
Shared Databases:
- Multiple services share the same database schema, leading to tight coupling at the data layer. This makes it difficult to change the database schema without affecting all the services, leading to data consistency issues and challenging database migrations.
Inter-Service Communication Overload:
- Excessive communication between services indicates they are not as independent as they should be. Frequent synchronous calls between services can lead to performance bottlenecks.
Why Do Distributed Monoliths Happen? 🧐
Understanding why distributed monoliths happen can help us avoid them. Here are some common reasons:
Inadequate Service Boundaries:
- Poorly defined service boundaries often lead to services that are too interdependent. Identifying the right boundaries for your services is crucial for achieving a true microservices architecture.
Lack of Domain-Driven Design (DDD):
- Without a thorough understanding of the domain and its subdomains, it’s challenging to define services that are cohesive and loosely coupled. DDD helps in creating well-defined service boundaries.
Database Coupling:
- Sharing a single database schema across services leads to tight coupling. Each service should ideally have its own database or schema to maintain independence.
Legacy Code and Practices:
- Migrating from a monolithic application to microservices without changing legacy code and practices can result in a distributed monolith. It’s important to refactor and rethink the architecture during the migration process.
Visualizing Different Architectures 📊
Let’s take a look at an insightful image that helps us understand different architectures, including monoliths, modular monoliths, microservices, and distributed monoliths:
- X-axis: Represents the “Number of Deployed Services”.
- Y-axis: Represents the “Modularity”.
Monoliths:
- Placed in the lower-left corner.
- Low modularity and a small number of deployed services.
- Indicates a single, large, tightly coupled application.
Modular Monoliths:
- Placed in the middle-left.
- Moderate modularity with a moderate number of deployed services.
- Represents a monolithic application divided into well-defined, loosely coupled modules.
Microservices:
- Placed in the upper-right corner.
- High modularity and a large number of deployed services.
- Represents an architecture where functionalities are split into independent services that can be deployed and scaled individually.
Distributed Monolithic:
- Placed slightly right of Monoliths but lower in modularity.
- Marked as an error with a red outline.
- Represents an architecture that has many services but still suffers from tight coupling, resulting in the same issues as a monolithic architecture despite having multiple services.
Impacts of a Distributed Monolith 🚧
A distributed monolith can have several negative impacts on your development and deployment processes:
Reduced Flexibility:
- The tightly coupled nature of services reduces the flexibility to deploy and scale services independently. This negates one of the primary benefits of microservices.
Increased Complexity:
- The system becomes more complex to manage. Coordinating changes and deployments across multiple tightly coupled services can be challenging and error-prone.
Performance Bottlenecks:
- Excessive inter-service communication can lead to performance issues. Synchronous calls between services can increase latency and reduce the system’s overall responsiveness.
Higher Risk of Failure:
- Tightly coupled services mean that a failure in one service can cascade and affect other services. This reduces the overall resilience of the system.
How to Avoid a Distributed Monolith 🛠️
Avoiding the distributed monolith antipattern requires careful planning and adherence to best practices:
Define Clear Service Boundaries:
- Use Domain-Driven Design (DDD) to define clear and cohesive service boundaries. Each service should represent a specific business capability or subdomain.
Decouple Data Storage:
- Ensure that each service has its own database or schema. This helps maintain independence at the data layer and reduces the risk of data consistency issues.
Minimize Synchronous Communication:
- Use asynchronous communication patterns where possible. This reduces the dependency between services and improves the system’s resilience and performance.
Implement API Contracts:
- Define and adhere to clear API contracts between services. This helps in reducing interdependencies and allows services to evolve independently.
Embrace Continuous Refactoring:
- Regularly refactor your services to address any emerging tight couplings or dependencies. Continuous refactoring ensures that the system remains maintainable and scalable.
📝 The Bridge: Modular Monoliths
Understanding and avoiding the distributed monolith antipattern is crucial for successfully implementing a microservices architecture. Remember, the goal is to create services that are independent, scalable, and maintainable.
Modular Monoliths strike a balance between the simplicity of a monolithic architecture and the organization of microservices. Instead of having one giant, tangled codebase, we divide the application into well-defined, loosely coupled modules. Each module is responsible for its domain but still resides within the same application. This approach keeps everything clean and organized without the overhead of managing a distributed system.
This is step-by-step development of reference Modular Monoltihs Architecture on .NET used ASP.NET Web API, Docker, PostgreSQL, Redis, RabbitMQ, Keycloak, Seq, MassTransit, Entity Framework Core, CQRS, MediatR, DDD, Vertical Slice Architecture and Outbox Pattern implementation with using latest features of .NET 8 and C# 12.
