Migrating Monolithic Applications to Microservices Architecture

applications vs microservices scaled
Bob Quillin October 20, 2021

Monolithic Applications vs Microservices

Wondering the differences between monolithic applications vs microservices? It can be confusing, but as more companies move to a cloud-first architecture, it’s important to understand these terms.

An enterprise application is usually made up of three parts – a client-side application, a database, and a server-side application. The server-side application itself consists of a web interface, a business logic layer, and a data layer. 

It may be built either as one large “monolithic” block of code, or as a collection of small, independent, and reusable pieces called microservices. Most legacy applications have been built as monoliths. Converting them to microservices has both benefits and challenges.

Monolithic Architecture

A monolithic architecture is one where all the components of an application are located within a single program. The web interface, business logic layer, and data layer are all combined in a single instance of the application. The application is deployed as one single unit, such as a JAR, WAR, exe, or something similar.

Microservices Architecture

A microservices architecture consists of services that are small, independent, and loosely coupled. Microservices are small autonomous services that perform a single task, like updating a customer address. 

Every service can be an independent application with its own programming language, development and deployment framework, and database. Each service can be modified independently and deployed by itself. A Gartner study shows that microservices can deliver better scalability and flexibility.

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Software Industry Problems and Priorities

Many are looking at monolithic applications vs microservices right now. Software companies want to be faster and more agile, release products more quickly, have shorter release cycles, and fundamentally support their companies in achieving Digital Transformation. 

The majority of mid-to-large companies have hundreds of legacy apps sitting in on-premise data centers and they want to move them to the cloud. They tend to transfer their apps to the cloud as-is, but this doesn’t work. Cloud apps need to be architected differently. What will help these companies achieve their goals faster – monoliths or microservices?

Monolithic Applications vs Microservices: Benefits of Microservices

There are many benefits to choosing a microservices architecture. These include scalability, agility, velocity, upgradability, cost, and many other factors. The Boston Consulting Group has listed the following benefits.

Emphasis on Capabilities and Values

Users of a microservice don’t need to know how it works, or what programming language it uses, or what its internal logic is. All that they need to know is how to call an API (Application Programming Interface) method provided by the microservice, and what data it returns. When designed well, microservices can be reused across applications.


A microservice is designed to be decoupled, so changes made to it will have no impact on the rest of the system. The developers don’t need to worry about complex integrations. This makes it easier to make and release changes. For the same reason, the testing effort can be focused, and this reduces testing time as well. This results in increased agility.


When comparing monolithic applications vs microservices, one of the biggest differentiators is upgradability, something that is critical in today’s fast-moving marketplace. A microservice can be deployed independently, so it’s easier to fix bugs and release new features. 

A single service can be rolled out without redeploying the full application. If issues are found during deployment, the erring service can be rolled back. This is easier than rolling back the full application. A good analogy is with the watertight compartments of a ship – flooding is confined. 

Small teams

A well-designed microservice is small enough for a single team to develop, test, and release. The smaller code base makes it easier to understand, so team productivity increases. Microservices are not coupled by business logic or data stores, so dependencies are minimized. All this leads to better team communication and reduced management cost.

Flexibility in the development environment

Microservices are self-contained. So, developers can use any programming languages, frameworks, databases, and other tools that they want. They are free to upgrade to newer versions or migrate to using different languages or tools if they wish. No one else is impacted as long as the exposed APIs are not changed. 


If a monolith uses up available resources, it can be scaled by creating another instance. If a microservice uses up all resources, only that service will need more instances. So scaling is easy and precise and the least possible number of resources is used, making it cheaper to scale.


When looking at monolithic applications vs microservices, the benefit of automation can’t be stressed enough. The use of microservices architecture enables the automation of several otherwise tedious and manual core processes such as integration, building, testing, and continuous deployment. This leads to increased productivity and employee satisfaction. 


All the benefits listed above result in teams focussing on rapidly creating and delivering value. This results in increased velocity. Organizations can respond quickly to changing business and technology requirements.

Why The Need to Transform Monolithic Applications to Microservices

So microservices offer several advantages over monolithic applications; yet, microservices are a relatively new concept. There are tons of applications that have already been developed as monoliths. Some of them are over twenty years old and are not cloud natives. 

It makes sense to refactor these monoliths into microservices-based applications to enjoy the benefits that microservices provide. According to McKinsey, the change from monoliths to microservices is one of the five major shifts that old and established companies should make to stay relevant.

Best Practices to Migrate Monolithic Apps to Microservices

There are two ways of migrating monolithic apps to microservices: manually, or through automation using software.

The migration process needs to consider several factors. The guidelines below have been recommended by Martin Fowler and are applicable whether you are trying to manually modernize your app or using automated tools.

Identify a simple, decoupled functionality

Start with functionality that is already fairly decoupled from the monolith, does not require changes to client-facing applications, and does not use a data store. Convert this to a microservice. This helps the team to upskill as well as set up the minimum DevOps architecture to build and deploy the microservice.

Cut the dependency on the monolith

The dependency of newly created microservices on the monolith should be reduced or eliminated. In fact, during the decomposition process, new dependencies are created from the monolith to the microservices. This is okay as it does not impact the pace of writing new microservices. Identifying and removing dependencies is often the most difficult part of refactoring.

Identify and split “sticky” capabilities early 

There may be “sticky” functionality within the monolith that causes several monolith capabilities to depend on it. This makes it difficult to remove more decoupled microservices from the monolith. It may be necessary to refactor the relevant monolith code to proceed. This can also be a very frustrating and time-consuming task.

Decouple vertically

Most decoupling efforts start with separating the user-facing functionality to allow UI changes to be made independently. This approach results in the monolithic data store being a velocity limiting factor. Functionality should instead be decoupled in the form of vertical “slices,” where each slice includes functionality encompassing the UI, business logic, and data store. Having a clear understanding of what business logic relies on what database tables can be the hardest thing to untangle.

Decouple the most used and most changed functionality

One goal of moving microservices to the cloud is to speed up changes to features existing in the monolith. To enable this, the development team must identify the functionality that is modified most frequently. Moving this capability to microservices provides the quickest and most ROI. Prioritize the business domain with the highest business value to refactor first.

Go Macro, then Micro

The new “micro” services should not, initially at least, be too small, because this creates a system that is complex and hard to debug. The preferred approach is to start with fewer services each offering more functionality, then breaking them up later on.

Migrate in evolutionary steps 

The migration process should be completed in small but atomic steps. An atomic step consists of creating a new service, routing users to the new service, and retiring the code in the monolith that was providing this functionality so far. This ensures that with every atomic step, the team is closer to the desired architecture.

Simplifying the Migration Process

When evaluating monolithic applications vs microservices, it’s clear that the process of converting a monolith manually to microservices is labor-intensive, manual, error-prone, time-consuming, and requires deep architecture skills. Most organizations lack these skills.

How about the automated way of migrating? Is that any better? Wouldn’t it be nice if one could simply input a monolith into a software modernization application (or platform) and all the time-consuming and complex steps above were accelerated and facilitated? The platform should enable and follow all the above best practices but in an automated, intelligent, and repeatable manner.

Broadly, the migration or modernization application should:

  • Help speed up modernization projects, thereby saving money
  • Automate the refactoring of complex apps, minimizing tedious manual effort
  • Be repeatable and self-service: monoliths in, microservices out
  • Intelligently and automatically transform complex monolithic apps into microservices
  • Analyze transactions, connections, and database table accesses and recommend refactoring of databases if required

Let’s look at what other capabilities such a migration application should have, and how it should work.


The application should perform static and dynamic code analysis, (and Data Analytics and Machine Learning if needed) to understand actual business flows. It should then identify logical entities and their dependencies.


It should analyze the complexity of the monolith to help prioritize and plan the next steps.


The application should enable the design and extraction of a new services UI. It should get rid of dead code and deploy efficient, compact microservices.

Factory Model

It should contain low-code automation to convert a monolith into equivalent microservices in a scalable and repeatable way.

Success measures

The migration application should work for all monolithic apps. It should offer the benefits of scale, velocity, agility, upgradability, and cost. It should not negatively impact security, velocity, and scalability. The migration should be performed speedily and in an intelligent and automated fashion.

An Ideal Platform for Migration: Does It Exist?

So, does such a platform exist today? It does. vFunction has been built from the ground up solely to automate and simplify the decomposition of monoliths into microservices. How does it do this?

The company uses modern tech, such as data science and machine learning, to identify business domains in the legacy monolithic app. It then uses this learning to build a new system architecture in which functionality is provided by a set of smaller applications, rather than by a single monolith.

The platform includes custom code analysis and visualization tools that watch the app running in real-time, and helps architects see how the app is behaving and what code paths are followed. This analysis of the code is used by the software to make recommendations on how to refactor and restructure existing spaghetti code. These tools help maximize exclusivity (resources that are used only by one service), enabling horizontal scaling with no side effects. It handles code bases of millions of lines of code, speeding up the migration process by a factor of 15.

Many companies attempt the decomposition process by using tools such as Java Profilers, Design and Analysis Tools, Java Application Performance Tools, and Java Application Tooling. But these tools are not designed to aid modernization. They can’t help in breaking down the monolith because they don’t understand the underlying interdependencies. So, the new architecture needs to be done manually.

In Closing

Companies want to move fast. The tools provided by vFunction enable modernization of apps (i.e. conversion from monoliths to microservices) in days and weeks, and not months or years.

vFunction is the first and only platform for developers and architects that intelligently and automatically transforms complex monolithic Java applications into microservices. Designed to eliminate the time, risk, and cost constraints of manually modernizing business applications, vFunction delivers a scalable, repeatable factory model purpose-built for cloud-native modernization. Request a demo to see how it works.

vFunction can help speed up software companies in their journey to become faster, more productive, and truly digitally transformed. If you want to see exactly how vFunction can speed up your application’s journey to being a modern, high-performant, scalable, true cloud-native, request a demo.

vFunction is headquartered in Palo Alto, CA. Leading companies around the world are using vFunction to accelerate the journey to cloud-native architecture thereby gaining a competitive edge.