In brief: How to modernize monolithic legacy applications with microservices step by step, using containers, APIs and cloud-native patterns to avoid disruption.
Monolithic applications that once served the business well now struggle under the weight of modern demands — slower release cycles, scaling bottlenecks, and single points of failure that put entire systems at risk. Microservices architecture solves these problems by decomposing applications into independently deployable services, each owning its own data and scaling on its own terms.
The traditional approach in software development is to create an application as a single structure consisting of multiple interconnected routines that form the application's components. The applications attempted a unified model of the entire business. The number of domains under the application sprawl was directly proportional to the complexity. This style of application is known as Monolithic in modern parlance.
Fast-forward to the present age. The same old huge enterprise monoliths still have to talk to external systems with ever-growing distinct domains that keep popping up with innovative ways of doing business. Systems with disparate canonical data models are continually being brought together and made to talk to each other.
Thus the unified model is increasingly being replaced with an approach of the bounded context where the domain within the bounded context can have its own canonical model.
As legacy applications face obsolescence both from a hardware and software perspective, enterprises are rethinking their replacement through modernization. One critical aspect of this modernization is migrating the Monolith applications to modern architecture. Complex interdependency between bounded contexts of sub-applications is eliminated through Microservices.
We have implemented microservices in several new applications and also as an additional upgrade to existing applications.
Critical Advantages of Microservices
- Requires low maintenance and testing effort
- Loosely coupled architecture
- Independently deployable services
- A small team of developers can own it
- Upgrade/scalability options are abundant
Among the various types of microservices, the two popular styles are containerized and serverless. Each type has its advantages and drawbacks. Containerized microservices are used by frameworks such as Spring Boot to create a self-sufficient standalone service that can be deployed in any compatible environment. A serverless option is more prevalent within the cloud environment.
Drawbacks to Consider
- A separate inter-service communication mechanism is required
- Handling failures is more complex due to the lack of common failure fallback mechanisms
- Implementing requests that span multiple services can become convoluted
- In the containerized type, all services are expected to run all the time
- In the serverless type, infrequently accessed services face cold start issues
- Microservices are stateless and do not have shared storage by default
Our engineers have the unique experience of migrating large scale high-loaded enterprise solutions running 24/7 with zero disruption, using a "parallel" approach. In this approach, the new application is built side-by-side with the legacy system. The legacy features are replaced one by one into the microservices architecture application components. Data synchronization approaches ensure users can work with both systems during the migration period.
Related solution: Digital Engineering — microservices and application modernization →
