Application architecture showdown: microservices, monolith, or modular monolith

When it comes to modernizing your legacy applications, you may think that moving from monolith to microservices is the only way. Similarly, when building a new service, a microservices architecture may seem like the natural choice due to its modern appeal.

But microservices aren’t a one-size-fits-all solution.

There are alternatives beyond the binary choice of monolithic and microservices architectures. A range of intermediate options exists, each offering unique benefits.

Choosing the right architecture can have a significant impact on the performance, scalability, and maintainability of your applications. That’s why we’ll explore the different types of architectures, namely monolith, modular monolith, and microservices, and help you decide which one is the best fit for your business.

Should you pick microservices architecture?

Microservices are a modern approach to building applications, where the application is broken down into small, independent services, each with its own responsibility. Each service can be developed, deployed, and scaled independently of the others. Communication between the services is usually through a well-defined interface, typically using APIs.

This style of architecture has become synonymous with modern application design, as many developers tend to associate it with the latest advancements in the field. Make no mistake, microservices do have their benefits, mainly deployment agility and precise scalability. And since each service is developed and deployed independently, it’s easier to introduce new features and updates without impacting the entire application. 

However, it’s essential to understand the challenges that accompany these advantages:

1. Complex architecture: Microservices, though robust, come with the intricacy of managing multiple databases, communication strategies, and deployment routes.

2. Operational overhead: The act of operating and supervising a multitude of services brings with it unique challenges.

3. Data consistency: Keeping data uniform and consistent across diverse services is a challenging endeavor.

4. Communication challenges: Initiating dialogue between various services for interlinked operations can cause latency.

Moreover, for many businesses, microservices might be excessive unless they’re operating on a grand scale, potentially causing costs to spiral.

Should you stay with monolith architecture?

A monolithic architecture is the traditional approach to building applications, where the entire application is built as a single, self-contained unit. In a monolith, all the components of the application, including the UI, database, and business logic, are tightly coupled and run in a single process.

Monolith gets a bad rap. For some, monolithic architecture is considered a relic of the past, and they’d prefer to see it evolve into a ‘zero-lithic’ approach to better suit modern application development. But all monoliths aren’t bad. Monolithic architecture has benefits like lower architectural complexity and high data integrity. And since there is only one database, it’s easier to maintain data consistency across the application. Also, the low complexity of the architecture allows every developer to understand what they have done, making it easier to onboard new developers and make fixes.

For small and maybe even medium-sized applications, monolith can actually be the best choice.

Monolithic architecture, while useful, has its set of complexities:

1. Scalability Issues: With growth, scaling becomes a challenge. You may find yourself needing to enhance the whole system, even when just a single part demands more resources.
2. Maintenance and deployment delays: The interdependence of components means that a minor tweak in one area necessitates a comprehensive retest and redeployment of the entire system, slowing down product releases.
3. Technological constraints: Monolithic structures typically rely on a single technological foundation, hindering the integration of newer technologies.
4. Vulnerability concerns: The interconnected nature means a glitch in one segment risks compromising the whole system.

Is modular monolith the right approach?

Modular monolith is an intermediate approach between monolith and microservices. It’s not exactly new, but it has gained more attention in recent years. In this approach, the application is divided into loosely coupled modules, each with its own responsibility. Each module can be developed and deployed independently, and the communication between the modules is usually through a well-defined interface.

The increased interest in modular monoliths can be attributed to the recognition that microservices, while beneficial in certain scenarios, may not always be the best choice for every application, particularly when considering the complexity and management overhead they can introduce. Modular monoliths offer a viable alternative for those seeking a more balanced approach that still allows for scalability and maintainability.

There are two types of modular monolith architectures: macroservices and miniservices.

1. Macroservices: In a macroservice, the application is packaged and deployed as a single unit, but the code is logically organized into modules. Macroservices have a shared runtime and database, which makes it easier to maintain data consistency across the application.

2. Miniservices: In a miniservice, each module is deployed separately, with its own runtime and a shared database. This approach allows for precise scalability, as we can scale only the required components of the application. However, this architecture can be more complex than macroservices, as each module requires its own deployment pipeline.

Modular monolith is a good option for applications that have outgrown the monolith architecture but are not ready for the complexity of microservices. It offers benefits like increased deployment agility, maintainability, and scalability.

How to choose the right architecture

So, how do you decide which architecture to choose for your application?

Beginning with pure monolithic architecture can limit your flexibility and scalability down the line. If you’re starting a new project and feel hesitant about diving into microservices, consider adopting macroservices or miniservices.

These options, falling under the modular monolith architecture, grant some of the advantages of microservices without overwhelming complexity. They allow you to segment your application into independently developed and deployed modules, yet maintain a shared database and runtime.

If, however, your team is well-versed in monolith and miniservices, transitioning to a microservices architecture might be a strategic move. This will give you greater flexibility and scalability, but it will also require more effort to manage multiple databases, communication protocols, and deployment pipelines. 

Factors to consider in architecture selection

Choosing the right architecture depends on various factors, such as the size and complexity of your application, the development team’s skill set, and the business requirements.

It’s also important to note that architectural decisions can vary for different functional components, rather than being a singular choice for the entire application.

Given these considerations, let’s delve deeper into the key factors you should consider. 

If the team is new to microservices, I recommend you begin with a modular monolith architecture, as it’s easier to understand and develop. As your application scales, you can migrate to microservices architecture.

However, if you have thoroughly assessed the costs, architectural complexities, and data integrity concerns, and are confident in your decision, microservices may be the right choice.

For modernizing a legacy monolithic application, making a direct leap to microservices can be challenging. Instead, consider adopting miniservices as an intermediate step. If the transition to miniservices proves successful, moving to microservices becomes a more manageable endeavor. Keep in mind that your chosen architecture is not set in stone and can evolve over time as the application progresses.