Monolithic (Legacy) vs. Microservices Application Development

Microservices are becoming increasingly popular and are considered to be the next flexible, scalable, and reliable approach. Without a doubt, many developers are rethinking their application development methods. However, while many have been quick to jump on the microservices bandwagon, moving from monolithic architecture is not a decision that you should make lightly. 

Before you decide the best way forward in your application development endeavors, it’s important that you understand the differences between legacy/monolithic architecture and microservices applications and the inherent pros and cons that each one holds. So, let’s dive in.

Contents

• What Is a Legacy Application?
• What Is a Monolithic Application?
• What Are The Pros and Cons of Monolithic Applications?
• What Is a Microservices Application?
• What Are The Pros and Cons of Microservices?
• When and Why Should You Choose Monolithic Development?
• When and Why Should You Choose Microservices Development?
• Combining monolithic and microservices: A hybrid approach
• What are the pros and cons of hybrid approaches?
• When to consider a hybrid approach?
• Choosing the right architecture for your application

What is a legacy application?

While monolithic applications are often referred to as legacy applications and vice versa, the two concepts are different. Many legacy applications are monolithic applications, but the term “legacy” actually refers to the state of development.

Typically, legacy applications are not being actively improved anymore, but they are being maintained enough to keep them running for the users who rely on them. Legacy applications eventually get phased out–either because the limited development of features and the user interface poses constraints for users or because the operations team decides they no longer want to maintain it.

In any case, migrating away from legacy applications and replacing them with something newer has many advantages for a business, but sometimes that approach presents just as many challenges. Rarely does a business rely on a legacy application because it lacks better options. Usually, there are better options, but moving to them is difficult because their business workflows are so tightly coupled with the legacy app.

What Is a monolithic application?

Many legacy applications fall under the umbrella of monolithic applications because monolithic development was extremely popular. Monolithic development creates single-tier applications where every component the application requires is built into itself. 

The design of a monolithic application means that making changes to a feature is complicated. There are so many dependencies within the large applications that even a small update is time-consuming, and it requires all users to download an entirely new version for things to work. That’s why most monolithic applications are approached with a waterfall software development process where changes might be released annually or semi-annually. 

Pros and cons of monolithic applications?

While the concept of monolithic applications might seem to contradict many modern best practices of application development, there are certain use cases where a monolithic approach might be ideal. Understanding the pros and cons of monolithic applications will help you decide if there’s ever a good time for you to take this approach. 

Pros of monolithic applications

• Monolithic applications are simple to build, test, and deploy, with regard to software engineering. Because everything is housed together, developers will favor how easy it is to actually launch the application initially, but maintenance down the road is a different concern. 
• Horizontal scaling is possible. Many people think that scaling a monolithic application is difficult. Still, they can actually scale horizontally fairly easily, and teams just need to run several copies of the app behind a load balancer to meet demand. Of course, this is most easily done in one direction because it’s hard to scale back once you’ve scaled up. 
• Fewer cross-cutting concerns. Given that monolithic applications have one codebase for everything, there are fewer cross-cutting concerns when it comes to logging and monitoring performance. 
• Improved performance. Since all the components in a monolithic application can share memory, they can boost performance because it’s faster than using service-to-service communications.

Cons of monolithic applications

• By nature, monolithic applications are fixed and linear instead of modular, and this contributes to the tight coupling of components. Entanglement and coupling impact the team’s ability to manage, scale, and update the application over time.
• One error can bring the whole thing down. Reliability is a major problem with monolithic applications. Because of the tight coupling of components, if one thing goes wrong in any module, it might make the entire application unusable.
• Updates require the entire application to be redeployed. Because there’s one large codebase with components so tightly coupled together, developers must re-deploy the entire application for every update. 
• Technology limitations. In order to design a monolithic application, developers must use the same technology stack throughout the application. Making changes to this tech stack down the road will prove costly.

What is a microservices application?

Microservices are not just an approach to development but a greater approach to systems software architecture that will have a ripple effect throughout an entire company. The concept is appealing, and it can offer a myriad of advantages, but that has led a number of businesses to adopt microservices without fully thinking through the complications of doing so.

To put it simply, microservices applications are applications that are loosely coupled. Instead of creating an all-encompassing application, like a monolith, the microservices approach seeks to break each application down into standalone functionality components, dubbed a “microservice.”

Most often, microservices are packaged into containers, which are runtime environments that only contain the elements absolutely necessary to run the microservice. This gives developers, for example e-commerce developers, the freedom to pick and choose microservices and piece them together like a puzzle, allowing applications to be assembled. With microservices, each service can be added, changed, or entirely removed independently of the other microservices that make up an application.

Pros and cons of microservices

The loose coupling and independence of microservices have made them a de facto standard for DevOps, but it’s important to realize that DevOps and microservices aren’t the right fit for everyone. Let’s explore the pros and cons of microservices to help you decide if it’s the right approach for your development projects. 

Pros of Microservices Applications

• Microservices are highly scalable. One of the biggest advantages of using microservices is that each component (i.e., microservice) can be scaled up individually and independently of the others, which makes optimizing resources very straightforward.
• Loose coupling simplifies changes. Since each microservice is loosely coupled to the others, development teams can easily test each component on its own and make changes to them over time. 
• Improved fault isolation. When one microservice breaks, it won’t take down your entire application. In fact, you’ll be able to work with that broken microservice independently and get it up and running again faster.
• Language and tech agnostic. With microservices, you can select the best programming language or platform for each individual service, which makes utilizing the best-matched skill sets and new technology easy. 

Cons of Microservices Applications

• Microservices go beyond development. Microservices architecture impacts systems, tools, methods, and many other components. Implementing microservices successfully starts with having a team that can support them.
• Tracking and monitoring can be extremely difficult. Breaking your apps down into multiple components makes development easier, but it makes tracking and monitoring things like performance and errors much more difficult and costly. To offset this, it is recommended to invest in a comprehensive container monitoring platform to gain full visibility into your microservices and containerized applications. 
• Implementation leads to many anti-patterns. Many teams end up completely offsetting the advantages of implementing microservices by failing to properly plan out the implementation process and effectively change their approach and infrastructure. That’s why moving to microservices takes a great deal of time and research.

When to choose monolithic architecture

With the rise of microservices popularity, many developers have been quick to dismiss “traditional” development approaches like monoliths. But microservices are not a one-size-fits-all solution.

Overall, you’ll want to choose a monolithic architecture if:

• You’re working with a small team. If you’re working on your own or with a small team, don’t put the complexity of microservices on your to-do list. A monolith will be able to meet your needs without making you change your entire approach to development.
• You’re creating a simple application. A small application does not have the requirements in regards to flexibility or scalability to justify pursuing microservices. A monolith approach will help you by keeping everything together.
• You know nothing about microservices. Microservices require an incredible amount of research and practice. You won’t see any business value if you or your team aren’t already experts in microservices.
• You want to launch quickly. A monolith application will help you develop and launch the solution as soon as possible, and it can reduce your initial costs and help you validate the idea sooner. 

When to choose microservices development

It’s easy to be enticed by all the benefits of microservices architecture and the potential that this development approach offers. However, microservices simply aren’t feasible for everyone. In fact, microservices applications can be needlessly costly and hard to monitor. 

Before you choose microservices for your applications, it’s important to remember that implementing microservices isn’t an easy feat and it’s not something you should take lightly. Make sure you can check these boxes:

• Your entire team has microservices expertise. You and your team have to possess the skills and knowledge necessary to effectively implement microservices architecture and follow the best practices. You also need relevant experience in things like DevOps, containerization, and domain modeling. 
• You have the appropriate resources. Appropriately implementing and managing microservices requires multiple dedicated teams. So, beyond expertise, make sure you have enough resources ready to devote to the endeavor. 
• You’re working with a complex application that needs to scale. Microservices architecture really shines when working with highly complicated applications that demand superior scalability. You’ll be able to add new features with ease and accommodate a large user base without missing a beat.

Combining monolithic and microservices: A hybrid approach

While the debate between monolithic and microservices architectures often presents them as mutually exclusive, many organizations find that a hybrid approach can offer the best of both worlds. By blending elements of monolithic and microservices architectures, businesses can strategically leverage the simplicity and straightforward deployment of monoliths alongside the flexibility and scalability of microservices.

What is a hybrid approach?

A hybrid approach involves integrating microservices into a primarily monolithic application or maintaining some monolithic components while developing new features as microservices. This strategy allows teams to modernize at their own pace, without the need for a full-scale migration to microservices all at once. For instance, a core set of stable features might remain in the monolith, while newer, more dynamic components are developed as microservices to enhance agility and scalability. 

What are the pros and cons of hybrid approaches?

This approach is particularly appealing for businesses looking to modernize their systems without the high upfront costs and risks of a complete overhaul. However, navigating a hybrid model isn’t without its challenges, and careful planning is essential to manage the increased complexity and integration demands.

Pros of a hybrid approach

• Hybrid models enable a gradual shift from monolithic to microservices architecture, reducing the immediate complexity and risks associated with a full migration. Teams can modernize specific application components step-by-step, prioritizing the most critical areas first.
• By retaining core monolithic elements, companies can avoid the extensive disruptions often associated with re-architecting an entire application. This ensures continuity and stability, especially for legacy systems that are deeply integrated with existing business processes.
• In a hybrid setup, microservices can be used to offload performance-critical or frequently updated components. This allows businesses to scale those particular services independently, without having to overhaul the entire application.

Cons of a hybrid approach

• Managing a hybrid architecture can introduce its own set of complexities. Teams must maintain the operational integrity of both monolithic and microservices components, requiring a careful balance of tools, skills, and processes.
• Ensuring seamless communication and data consistency between monolithic and microservices components can be challenging. Hybrid systems often require robust API management and integration strategies to handle the increased interactions between different architectural styles.

When to consider a hybrid approach

A hybrid approach can be particularly beneficial when dealing with large, complex legacy systems that cannot be easily decomposed into microservices. It’s also a good fit for organizations looking to explore the benefits of microservices without committing to a full transition immediately. By adopting a hybrid strategy, teams can take a more measured and risk-averse path to modernizing their application architecture.

Ultimately, the choice to adopt a hybrid approach should be guided by your specific application needs, team capabilities, and long-term goals. By carefully planning and implementing a hybrid architecture, businesses can leverage the strengths of both monolithic and microservices models to set their applications up for long-term success.

Choosing the right architecture for your application

The question of monolithic vs. microservices is being asked more and more every day, but don’t let the excitement of microservices fool you. While microservices have a number of use cases, you shouldn’t be so quick to dismiss monolithic applications–especially if you’re working with a small app or small team. From here, it’s up to you to choose the best option for your next development project.