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Arslan Ahmad

Monolithic vs. Service-Oriented vs. Microservice Architecture: Top Architectural Design Patterns

System Design Interview Preparation: Mastering the Art of System Design.
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In today’s technology-driven world, the architectural design of software systems is pivotal. It influences the efficiency and flexibility of the systems and also impacts their adaptability to future changes. Yet, it remains one of the most challenging aspects in the field of software engineering. Thus, today, we will embark on a deep dive into three of the most widely recognized architectural styles in software design: Monolithic, Service-Oriented (SOA), and Microservices.

Every project has unique demands, and understanding these architectural styles can help guide us to the optimal approach for each project we undertake. This blog aims to compare and contrast these three architectural designs, highlighting their strengths, weaknesses, and best use cases. We’ll dissect these architectures, peek under their hoods, and leave you with a solid understanding to help navigate the architectural landscape.

Whether you’re a seasoned software engineer, a student dipping your toes into the vast sea of software architecture, or an entrepreneur looking to understand which architecture style suits your next big tech venture best, this blog is for you.

Let’s start with a brief look at the three architectural styles.

1. Monolithic Architecture

First, let’s tackle Monolithic Architecture — a traditional model and often the first stepping stone for many budding developers. Everything in a monolithic architecture, from UI to data access code, is packaged as one tight unit. In this model, components are interconnected and interdependent. If a single component needs to be updated or scaled, the entire application must be scaled or redeployed.

Advantages:

Simpler to develop, test, and deploy since it’s a single system. Inter-component communication is fast because everything is in the same process.

Disadvantages:

The entire application can be impacted by a single component’s failure. Deployment of updates can be slow and risky. It can be challenging to scale because scaling requires duplicating the entire application.

2. Service-Oriented Architecture (SOA):

In a service-oriented architecture, the application is designed as a collection of reusable services which are network-accessible. These services communicate with each other to perform tasks. SOA often has an enterprise service bus (ESB) which handles message routing, choreography, and applying business rules.

Advantages:

High reusability of services. Can be distributed over a network, leading to better fault isolation.

Disadvantages:

The use of an ESB can create a single point of failure and can limit scalability. Can be complex due to the need for a middleware system.

3. Microservice Architecture

A microservice architecture breaks down the application into small, loosely coupled services that can be developed, deployed, and scaled independently. Each microservice typically implements a single business capability and uses simple APIs for communication.

Advantages:

Provides flexibility in using different technologies for different services. Independent deployment and scalability. Faster deployment and easier understanding of codebase for new developers.

Disadvantages:

Increased complexity due to the need to coordinate between many different services. More difficult testing due to distributed deployment. Network latency and data consistency can be challenging.

Take a look at Grokking Microservices Design Patterns to master microservices design patterns for designing scalable, resilient, and more manageable systems.

Top Design Patterns for Monolithic Architecture

Here are five common architectural patterns used in monolithic structures:

  1. Layered Pattern: This pattern divides the monolith into logical layers, with each layer having specific duties and responsibilities. For instance, a typical three-layered architecture includes the presentation layer (UI), business layer (business logic), and data layer (database operations).

  2. Model-View-Controller (MVC): MVC is a pattern used in web applications. The model corresponds to application data, the view to its user interface, and the controller to the part of the system responsible for managing input, updates to the model, and changes in the view.

  3. Pipe and Filter: This design pattern helps to structure systems which process a stream of data. Each processing step is encapsulated in a filter component. Data to be processed is passed through pipes. These pipes can be used for buffering or for synchronization purposes.

  4. Client-Server: In this pattern, the system is divided into two main components: the server, which provides services, and the client, which accesses these services. In monolithic applications, the client and server run on the same machine and communicate via the function call mechanism.

  5. Blackboard: This pattern is useful for problems for which no deterministic solution strategies are known. In Blackboard, several specialized subsystems assemble their knowledge to build a possibly partial or approximate solution. The blackboard component is a structured global memory containing objects from the problem domain.

Top Design Patterns for Service-Oriented Architectures Architecture

Here are five prevalent design patterns used in Service-Oriented Architectures (SOA):

  1. Service Registry: This is a database that acts as a repository of services, where service providers can publish their services and consumers can look them up. It simplifies the process of finding and invoking services in a distributed environment.

  2. Enterprise Service Bus (ESB): This acts as a communication center that manages communication and message routing between services. It can decouple systems from each other, and provide additional services like message transformation, routing, and applying business rules.

  3. Service Facade: This pattern provides a unified, higher-level interface to a set of interfaces in a subsystem. It helps to reduce the complexity of interactions between services and enables loose coupling.

  4. Message Bus: This pattern allows general communication between components without requiring components to have knowledge of the system they are part of. The key idea is to introduce a third party (message bus) to deliver messages to the components.

  5. Composite Services (Orchestrated Choreography): This design pattern enables you to assemble coarse-grained services from finer-grained services. It’s a way of creating a workflow of services where you coordinate or compose services to create a service providing higher-level functionality.

Top Design Patterns for Microservices Architecture

Here are five famous design patterns used in microservices:

  1. API Gateway: In a microservice architecture, clients often need data from multiple services. Instead of making calls directly to each microservice, the client makes a few consolidated calls to an API Gateway, which then orchestrates the microservices required to handle the request. This pattern simplifies the client-side code and reduces the number of round-trip calls between client and server.

  2. Circuit Breaker: Given that microservices often depend on each other, the failure of a single microservice can cascade to other services. The circuit breaker pattern helps prevent this. When a network call from a service fails repeatedly, the circuit breaker trips, and for a subsequent period, all attempts to invoke the service will fail immediately. After a timeout, it allows a limited number of test requests to pass through. If these requests succeed, the circuit breaker resumes normal operation; otherwise, the timeout period begins again.

  3. Saga: In a microservices architecture, achieving data consistency across services can be challenging. The Saga design pattern is a way to manage data consistency across services in a microservice architecture. Sagas are a sequence of local transactions where each transaction updates data within a single service. If one transaction fails because it violates a business rule, then the saga executes compensating transactions to undo the impact of the preceding transactions.

  4. Service Discovery: Given that microservices run on different machines or containers, it’s important for services to be able to find and communicate with each other. The service discovery pattern provides a database for microservices to register their locations and enables other services to locate them.

  5. Event-Driven Architecture: Microservices often need to communicate with each other to stay in sync. Instead of direct communication, services can asynchronously publish events that represent state changes. Other services can then subscribe to these events and update their own state accordingly. This approach decouples services and provides a natural way to maintain consistency across services in a distributed environment.

Conclusion

In the end, the decision between Monolithic, Service-Oriented, and Microservices architectures is not a one-size-fits-all answer, but rather a nuanced choice based on the specific needs of the project at hand.

Throughout our discussion, we’ve seen the simplicity and ease-of-use of Monolithic architectures, the balance and reusability offered by Service-Oriented Architectures (SOA), and the independent scalability and flexibility of Microservices. Each has its strengths and its trade-offs.

Remember that architectural patterns are not meant to bind us but are tools designed to make our work easier and more effective. Choosing an architecture is not about picking the latest trend; it’s about understanding your application’s needs, your team’s expertise, and your organization’s long-term goals. It’s about foresight, anticipating changes, and making choices that will help not hinder your adaptability to those changes.

In the ever-evolving world of software development, our understanding and implementation of architectural patterns will continue to grow and evolve. The key is to stay informed, adaptable, and above all, open to learning. As software developers, our goal is always to build software that is efficient, maintainable, and most importantly, serves the needs of its users. The architecture we choose plays a crucial role in achieving this goal.

Want to learn more about system design and design patterns?

➡ Take a look at Grokking Microservices Design Patterns to master microservices design patterns for designing scalable, resilient, and more manageable systems.

➡ Check Grokking System Design Fundamentals for a list of common system design concepts.

➡ Learn more on architecture and system design in Grokking the System Design Interview and Grokking the Advanced System Design Interview.

Keep learning more on system design interviews:

  1. Mastering the System Design Interview: A Complete Guide
  2. Ace Your System Design Interview with 7 Must-Read Papers in 2023
  3. System Design Interview Survival Guide (2023): Preparation Strategies and Practical Tips
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