From monolith to microservices: how to modernize legacy applications on AWS
Monolithic systems usually work well at first, but as the company grows, this type of architecture becomes an obstacle.
Any small change requires testing and deploying the entire system, scaling means duplicating the whole application even when only one part is under high load, and different teams end up competing over the same code to ship new features. Migrating to microservices solves much of these problems, but it needs to be done carefully.
What characterizes a monolithic system?
A monolith is an application built as a single unit, where all functionality, from user registration to payment processing, shares the same code, the same database, and the same deployment process. This makes initial development easier, but complicates maintenance as the system grows.
What are microservices?
Microservices split that same application into smaller, independent services, each responsible for a specific part of the business, such as authentication, product catalog, or order processing. Each service can be developed, deployed, and scaled independently, without directly affecting the others.
Why is making this transition all at once risky?
Rewriting an entire monolithic system all at once usually takes months, freezes the development of new features during that period, and creates a high risk that the final result won’t work as expected, since all validation happens only at the end of the project.
The strangler fig pattern as a safer approach
A safer approach, known as strangler fig, extracts functionality from the monolith one piece at a time, creating independent microservices for each part, while the rest of the system keeps running normally. Over time, more and more functionality leaves the monolith, until it ceases to exist or is restricted to a small, non-critical part of the system.
This approach lets you validate each new service in production before moving on to the next part, reducing risk compared to a complete rewrite.
AWS tools to support this modernization
Amazon ECS and Amazon EKS let you run microservices in containers, with independent scalability for each service. AWS Lambda lets you implement specific functionality in a serverless format, without managing servers. Amazon API Gateway centralizes and manages communication between the microservices and the application’s external clients.
How to prioritize which parts to extract first?
It’s worth starting with the functionality that changes most frequently, that has the greatest need to scale independently, or that has already caused performance problems within the monolith. Extracting these parts first usually generates the fastest and most visible return of the modernization project.
What changes after the transition?
Teams start developing and deploying their parts of the application independently, without waiting for a single, shared deployment cycle. Each service scales according to its own demand, reducing resource waste. And failures in one part of the system no longer bring down the entire application, increasing overall resilience.
CloudDog leads legacy application modernization projects on AWS, migrating from monoliths to microservices safely and without stopping the operation. Learn about our Cloud Modernization service and plan the transformation of your legacy architecture.
