Microservices vs Service-Oriented Architecture (SOA): Fundamental Differences

With increasing complexity and demand for highly scalable and robust applications, conventional monolithic architecture is no longer the best choice. After a certain threshold, monolithic architecture tends to hinder application performance and scalability. Moreover, with an enormous codebase, making changes to the tightly coupled, dependent processes in the monolithic architecture drastically increases the impact of single process failure.

To deal with these limitations of a monolithic architecture, developers have adopted the Single Responsibility Principle coined by Robert C. Martin (co-author, Agile Manifesto), which says: Gather together those things that change for the same reasons and separate those things that change for different reasons.

Eventually, Service-Oriented Architecture (SOA) and Microservices Architecture gained acceptance and enabled developers to build applications as a suite of small, de-coupled services, running in their own environments and are independently deployable.

While Microservices and SOA have application modularity in common, they differ in how the services are deployed and the size of modules. Before we understand the fundamental differences between the two- Microservices vs SOA, let’s understand these architectures in detail.

Microservices: An Overview

Microservices is a software modularization approach that aims at dividing a large software system into smaller components. With a microservices architecture, an application is built with an independent group of components that run each application process as a service. Such an architecture makes it easier for applications to scale, accelerate the development process, offers space for experimentation, and reduce time-to-market for new features.

Microservices Architecture: Benefits

• Continuous Development and Deployment

Each component in a microservices architecture is developed, deployed, operated, and scaled independently, i.e. a change in one service does not affect the functioning of other services. Moreover, these services do not share code or implementation with other services. This ensures continuous development and deployment of large, complex applications.

• Eliminates Technology Commitment

Microservices can be created using different technologies (frameworks, languages, or OS). Therefore, it eliminates any long-term commitment and dependability on a particular technology stack. While building a new service or updating an existing one, a new, better technology stack can be chosen.

• Improved Fault Isolation

Since all services in an application are independent of each other, any halt in a process does not affect another. For example Memory leak in a particular service will not have any impact on another service, ensuring that the rest of the services keep receiving and handling incoming requests. If this is compared to a monolithic architecture, a single misbehaving component affects the entire system.

Large Scale Websites are using Microservices Architecture:

Realizing these benefits, organization are moving from monolithic architecture to microservices. For instance, Netflix, one of the most popular video streaming service is one of them. It handles over a billion calls per day on their video streaming API, from over 800 kind of devices. Each API call is then spread out to an average of six calls to backend services.

Microservices are being used to re-architect existing applications as much as for brand new project, according to Red Hat 2017 Microservices Survey. 

Service Oriented Architecture (SOA): Overview

Similar to Microservices, SOA is a software modularization approach, an architecture based on disparate services. Herein, a service is a well-defined, self-contained functionality. In the  SOA architecture, different services communicate with each other to execute a functionality.

The SOA services are loosely-coupled, i.e. a service interacting with another might not know the technical details of another service. An SOA service consists of two fundamental components: Service Consumer that requests for some service and Service Provider that returns the result for the request.

Since Microservices and SOA enable developers to build independent services to build an application; they more or less share similar set of benefits. However, there are some basic differences between the two, which will be shared in the later segment.

Service Oriented Architecture: Benefits

• Legacy System Compatibility

SOA is advantageous when integrating with legacy systems. It provides a structured and standardized approach to connecting modern applications with existing systems, allowing organizations to modernize and extend the life of their legacy applications.

• Optimized Resource Utilization

By promoting the reuse of services, SOA can lead to more efficient resource utilization. Services can be developed once and leveraged across multiple applications, reducing redundancy and minimizing development costs in the long run.

Example : Amazon, particularly in its early days, embraced SOA principles to build a scalable and flexible architecture. SOA played a crucial role in Amazon's ability to evolve from an online bookstore to a vast e-commerce platform offering diverse products and services. It allowed different business units to operate independently while integrating seamlessly.

Microservices vs SOA: Differences

In both the architectures, each service has a certain responsibility, unlike a monolithic architecture. Thus, developers have the flexibility to develop the services in different technologies, which enables the team to choose the most relevant use-case fit for a service. However, both the architectures differ in following terms:

1. Fault Toleration

Microservices vs SOA, another point of differentiation is fault toleration. In SOA, an Enterprise Service Bus (ESB) can be a single point of failure, which impacts the functioning of entire application. An Enterprise Service Bus (ESB) implements communication between mutually interacting applications in SOA. It can perform a variety of functions, ranging from message transformation, routing, logging, protocol transformation, acting as security gateway, etc. If one of the ESB services slows down, it will clog up the requests for that service. In comparison to SOA, microservices are fault tolerant as all services and their deployment is independent of each other.

2. Resource Utilization

Microservices can lead to more efficient resource utilization as services scale independently, and resources are allocated based on specific service demands. In SOA, resource utilization might be optimized through shared services, where multiple applications or processes leverage common services. This can reduce redundancy but may create dependencies.

3. Development and Deployment Speed

Microservices facilitates faster development and deployment cycles due to smaller codebases, independent deployment, and agile team structures. However, in SOA, deployment cycles may be longer due to a more centralized approach and dependencies between services. Rapid changes across the entire architecture might require careful coordination. 

4. Operational Overheads

Microservices, while offering flexibility, can introduce operational complexities due to the need for managing a larger number of services, each with its deployment and scaling requirements. Whereas, SOA has a more structured approach to operations, which can be advantageous for organizations that prefer a standardized and controlled environment. However, it may be less adaptable to rapid changes.

5. Communication Protocols

Microservices typically use lightweight communication protocols like HTTP/REST or messaging systems. Communication between microservices is often stateless, promoting flexibility and simplicity. While SOA may involve a variety of communication protocols, including heavyweight protocols such as SOAP (Simple Object Access Protocol). The communication style can be more formalized and may include features like transactions.

6. Data Consistency 

Microservices tend to favor eventual consistency models, where data consistency is achieved over time. Each microservice manages its database, and achieving immediate consistency across all services can be challenging. While SOA often emphasizes immediate consistency, with a centralized data store or a more tightly coupled approach. Maintaining a consistent state across services is a priority.

Use Microservices When:

Your project is large and complex, with the need for independent development, deployment, and scalability of individual components.

Scenario: Your application experiences varying workloads, and you need the ability to scale specific services independently.

Scenario: Different services in your application require specific technologies or frameworks.

Scenario: Your project has rapidly changing requirements, and you need the ability to deploy updates to individual services without affecting the entire application.

ALSO READ: 5 Grounds for Building A Robust Microservice Architecture

Use Service-Oriented Architecture (SOA) When:

Your project is more straightforward, and you prefer a centralized approach to development and governance.

Your project benefits from a standardized technology stack across services for easier integration and maintenance.

Your project has stable and well-defined requirements, and the workloads are predictable without frequent changes.

Your development team is centralized and prefers a more coordinated and less decentralized development approach.

Your project has strict industry compliance requirements, and a standardized approach is necessary.

In summary, the choice between Microservices and SOA depends on the specific characteristics, goals, and constraints of your project. Understanding these factors will help you make an informed decision that aligns with the architecture best suited to meet your project's needs.