Service-Oriented Architecture vs Microservices – differences

In one of our recent posts, Introduction to microservices, we explained exactly what they are, how they work, and what benefits microservices have. This topic is very hot due to the growing demand for highly scalable, reliable applications. The increasing complexity of emerging systems makes monolithic architecture a thing of the past. All because it tended to lower performance once the app reached a certain size and hence, better alternatives were needed for them. 

Service-oriented architecture (SOA) and microservice architecture have just taken its place. Due to their similarity, there is some confusion with them and even doubts whether they differ at all. We also touched on this issue in the above-mentioned post, but it should be looked at in more detail. But before we get into the fundamental differences between SOA and microservices, let’s take a closer look at these architectures.

What is Service-Oriented Architecture (SOA)?

Service-oriented architecture (SOA) is a software design style in which services are delivered to other components through a communication protocol over a network. SOA integrates distributed, separately maintained and deployed software components. It is based on specific core values, many of which also apply to microservices, such as flexibility, business value over technical strategy, evolutionary improvement, or internal interoperability. A service has four properties according to one of many definitions of SOA:

• It logically represents a business activity with a specified outcome;
• It is self-contained;
• The consumer does not have to be aware of the service’s inner workings;
• It may consist of other underlying services.

In SOA, services use protocols that describe how messages are passed and analyzed using description metadata. This metadata describes both the functional characteristics of the service and the quality of service characteristics. SOA aims to allow users to combine large chunks of functionality to build applications that are built exclusively from existing services and connect them offhand. The service presents the requester with a simple interface that eliminates basic complexity by acting as a black box. Other users can also access these independent services without knowing about their internal implementation.

What are Microservices?

Microservices is a variant of the service-oriented architecture structural style that organizes an application as a collection of individual services. This construction implies some characteristics of them:

• independently deployable, autonomously developed and implemented using different technologies each, depending on what is the best solution;
• fine-grained and the protocols are lightweight;
• small in size, messaging-enabled, bounded by contexts and decentralized;
• built and released with automated processes;
• organized around business capabilities;
• use technology-agnostic protocols such as HTTP.

Microservices are prominent in their flexibility. Instead of a single, monolithic code, they propose building an application as a set of services. All functionality is divided into independently deployable modules that communicate with each other using API (Application Programming Interfaces). Each service has its scope and can be updated, deployed and scaled apart from the others.

Read also: Microservices vs API – What is the Difference?

What are the key differences between SOA and Microservices?

As you see, microservices are a variant of service-oriented architecture structural style, so they have many common attributes. The differences start when we talk about the more detailed properties of them both:

• Code reuse – in SOA, it’s strongly wanted and even essential at an enterprise level. In a microservices architecture, reusing components results in dependencies that reduce agility and resilience. 
• Microservices are focused on decoupling and prefer to reuse code by copy and data duplication.
• Service granularity – the components of SOA can range from small, specialized to enterprise-wide services. Microservices architectures are made up of specific, specialized services, each of which is designed to do a single job very well.
• Data storage – SOA involves sharing data between services, and in turn, in microservices architecture, each service can have independent data storage.
• Reusability – SOA maximizes taking advantage of sharing a common architecture. However, it also causes SOAs to run slower than microservice architectures that gain time from duplication. 
• Communication – with microservices, the communication is executed via a simple messaging system, while SOA uses Enterprise Service Bus (ESB).

Pros and cons of SOA

Advantages of SOA:

• High reusability – services can be reused independently of their previous interactions with other services;
• Scalability – a system is easy to scale as multiple tiers of one service can run simultaneously on different servers;
• The possibility of parallel development – thanks to the layer-based architecture, developers can work on independent services and deliver them quickly. This not only reduces cost but also increases productivity;
• Independent location – it doesn’t matter where the services are located. They can be published on one or several different servers. 
• Easy debugging – services usually are small in size as compared to the full-fledged application. Therefore, it is easier to debug and test the independent services.

The disadvantages of SOA:

• High investment costs – although SOA is an excellent choice for further business development, its implementation is usually expensive.
• A large variety and number of services – due to its structure, the application can constantly generate messages while performing tasks. Consequently, the number of these messages becomes overwhelming, which makes it difficult to properly manage services.
• Slower response time and load – there is bigger overhead when a service interacts with another service, and so, this increases the response time.

Pros and cons of Microservices

The service separation approach offers many opportunities and benefits:

• Flexibility – as microservices are deployed apart from each other, it is easier to manage bug fixes and feature versions. The service can be updated without having to redeploy the entire application and roll back the update if something goes wrong.
• Scalability – services can be scaled independently, e.g. those that require more resources, without the need to scale the entire application.
• Diversity of technologies – each microservice can be made in a different technology, which allows for the selection of the most efficient solution for each part.
• Easy error fixing – if one microservice becomes unavailable, it does not disrupt the entire application, as long as all parent microservices can handle errors properly.
• Small, dedicated teams – it enables the development of each of the services by one team, which therefore focuses only on the functionality of this service.

They also have some cons, which is also worth keeping in mind:

• Complexity – although the individual services are simpler, the overall system is more complex.
• Data integrity – individual microservices are responsible for the persistence of their data. As a result, it can be difficult to maintain data consistency.
• Too big variety – the languages ​​and structures used can be so diverse that maintaining the application becomes difficult. It may be useful to introduce project-wide standards without too much limiting the flexibility of the teams.
• Network overload and lag – using many small, precise services can increase communication between services. Additionally, if the service dependency chain becomes significantly longer, additional latency may become an issue. Therefore, you should carefully design your APIs.
• Skills needed and difficult management – microservices are highly distributed systems. Correlation of logging between services can be an issue. Typically, logging should correlate multiple service invocations for single-user operation. Consider carefully whether your development team has the skills and experience required to work with microservices.

Microservices vs SOA: Which is better for your project?

There is no clear answer to this question – the devil is in the details. It all depends on your business goals, as well as the type and characteristics of the project you want to start working on. Both solutions have their advantages and disadvantages, as we have already shown above.

If you focus on high scalability and you want to frequently deploy new versions of the same service, choose microservices. Besides, this architecture is more fault-tolerant as a problem with one service does not affect the performance of the other services. Each of them works independently. Also, when it comes to SOA, chances are it can create additional problems. If the ESB stops responding properly at any time, all services will be affected. ESB is the only means of communication available, and when a single service sends too many requests, it can become congested. In this regard, microservices perform better, because in this architecture each service works independently. Therefore, if one microservice goes live, the problem remains and does not affect other services. Note that microservices and SOA provide different possibilities in terms of size and scope, and SOA is usually much larger.

You can choose SOA if you are building a complex application. It will be more difficult to manage as more features are added, but you will save time and you can reuse the code. Moreover, if your application needs to communicate with different architectures, SOA eliminates the adoption process. This solution is usually chosen for large corporate projects.

Microservices, in turn, will be just right for smaller applications. They provide flexibility, as well as allow further scalability and great control for the developer. If your team wants to take full control of the project and make changes on the fly, without worrying that some features might break, microservices are your best bet. This option also allows you to get your application to market faster and create an MVP.

Summary

We hope we have cleared up the question of the difference between service-oriented architecture and microservices. These are often just nuances, but if you want your project to be a success, you need to think carefully about which solution will be more appropriate. If you’re still having a hard time deciding, you can trust our experienced specialists to help you make the best decision.