From monolith to microservices: how to evolve your legacy

6 minutes read
13 March 2020

The digital transformation brings technological, software, and application innovations, which are proving to be extremely beneficial for companies. For this reason, more and more companies are adopting new software development paradigms. However, in order to achieve successful implementations, in many projects, there is an important obstacle to overcome: the modernization of processes and paradigms.


Monolithic application: what is it?

Applications were formerly developed and distributed as single units: monolithic applications, with a single code base, easy to implement in small dimensions, but unsuitable for growth and evolution. The essential components of an application with a monolithic architecture (user interface, authorization system, database, and business logic) are combined and integrated into a single program.

If we take an e-commerce website as an example, we can easily see that its realization, according to the monolith model, would require the implementation of all functions – from the display of products, to the cart, to the payment functions – through a single code base, that, as the application grows, could generate major management problems.


Why they are hard to manage

The applications that are based on a monolithic software structure have several limitations. Let’s see them in detail.


When you need to edit, update, or add functionalities, the code base increases making the application grow. When an application becomes too big and complex, it is also difficult to entirely understand it and make changes, even small ones, without touching the entire system.


With this architecture style, it is difficult to make frequent releases, because when you need to update a component, the entire application must be deployed from scratch. There is also the chance that the components, that have not been directly involved in the editing, are damaged or slowed down. Therefore, these risks, that are associated with redeployment, end up discouraging frequent updating practices.


Since a monolithic application contains all the functions and it is characterized by an architecture in which the services are closely integrated and interdependent, it is difficult to scale: the editing of a single part impacts the entire application.

In order to solve this problem, the solution is to generally implement the horizontal scalability, by duplicating that function in a cluster, or by creating new instances of the application itself.


The occurrence of a malfunction in any module of the program can potentially compromise or block the entire process and the application availability.


Microservices: what they are and how they can help

Microservice architecture represents an innovative method of developing software: an application can be created by developing numerous independent modular services, which interact with each other to carry out the same activities. Basically, every application component can be independently implemented and run as a service; in addition, it is responsible for a specific function and it is able to communicate with others through API (Application Programming Interface). In this architectural model, the service malfunction that may occur would not necessarily compromise the entire application functioning.

By keeping in mind the e-commerce example mentioned above, that was created according to the microservice method, it can be modified and easily scaled in all its components.

For instance, if you need to change the payment gateway, you can directly work on the microservice that is in charge of that functionality, without affecting the other parts of the application.


Microservices and cloud-native: advantages compared to monolithic application

The microservices approach, thanks to the most modern technologies, such as Kubernetes, Docker, and containers, can also be included in the cloud-native application development model. This model allows to decouple the software from the hardware and to take advantage of the cloud in terms of flexibility and agility in resource management.

Leveraging on a distributed architecture, the cloud-native application development model with microservices brings various benefits.

Development Agility

Different developers can simultaneously work on single components and services that belong to the same application. And this allows streamlining the design cycle and reducing the time-to-market.

Support of CI / CD strategies

The microservices facilitate the application of the continuous integration and continuous distribution (CI / CD – continuous integration / continuous deployment) methodologies of the code, that is at the basis of the DevOps model. For example, when a component needs to be updated, you need only to deploy that particular service, and not the entire application.


Each service can be independently scaled and distributed across multiple servers and infrastructures.


With a microservices architecture, if a malfunction happens in a component/ service it will not affect the functioning of the others, because each of them has been independently developed. In this way, unlike an application with a monolithic architecture, the application built with microservices does not collapse, but continues to work and, in the meantime, it is possible to repair the problem in the malfunctioning component and then deploy it again.


Modernize systems

Microservices development, that is built according to the cloud-native model, can be used to evolve legacy systems: outdated business software systems, based on obsolete code, are still widely used because they are important for the company. These IT systems are typically linked to a centralized architecture that is very difficult to interface with modern systems and with the different channels.

Since the legacy systems support mission-critical functions, they cannot (and must not) be eliminated or replaced, but they can be modernized, by applying a layer of software on them, which is capable of realizing all the customized business services and logics necessary for the company.

This layer of software is the microservices platform, which allows you to separate the underlying legacy systems from the custom logics. With an incremental approach, it is possible to create all the necessary services and customizations, keeping legacy systems alive and lightening their workload. Hence, it is possible to make the systems evolve over time and, if necessary, to replace – for example – an outdated management system with a more modern one, without interrupting the processes and avoiding losing the evolution reached by other components (channels, internal apps, business intelligence etc.).

The benefits are both in terms of productivity – implementation, updating, scalability and distribution of applications – and in terms of management of development cycles – offering an experience of automated and optimized development and management.


In conclusion, evolving monolithic applications and corporate legacy systems provides the company with many advantages that also means a reduction in time-to-market, reduction of IT costs, and customer experience improvement.


Mockup from Freepik 

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Monolithic application: what is it?
Why they are hard to manage
Microservices: what they are and how they can help
Microservices and cloud-native: advantages compared to monolithic application
Modernize systems