Breaking up a large Java application can speed up delivery and make systems more resilient. Done carelessly it creates a distributed mess. This guide describes an incremental approach that works.
First, ask whether you need to
Microservices add network calls, distributed data and operational overhead. If your main problem is messy code, a modular monolith may be enough. Consider splitting when separate teams are blocked by shared releases, or when one part of the system needs very different scaling.
Find boundaries that follow the business
Good services line up with business capabilities such as billing, catalog or notifications, not with technical layers. Look at where the code changes together, where data is naturally separate and which teams own which decisions.
Use the strangler pattern
Instead of rewriting everything, put a routing layer in front of the monolith and move functionality out one slice at a time. Each new Spring Boot service takes over a piece of traffic while the rest keeps running in the old application. If a slice goes badly, route back.
- Pick a low-risk, valuable first slice
- Build the service behind a stable API
- Run old and new in parallel and compare results
- Shift traffic gradually
- Delete the old code once it is unused
Give each service its own data
Services that share a database are still coupled. Plan data ownership early. Move tables with the service that owns them, expose data through APIs or events, and accept that some reports will need a separate reporting store.
Build the platform basics first
Before the second service, set up automated builds and tests, container images, central logging, metrics, tracing and a repeatable deployment path. With Spring Boot and Spring Cloud, much of this is available as standard building blocks, and AWS ECS gives a dependable place to run the containers.
Common mistakes
These show up again and again:
- Splitting too small, creating dozens of services nobody can understand
- Chatty synchronous calls that turn one failure into many
- No contract tests, so one team's change breaks another
- Ignoring operations: no monitoring, no on-call, no runbooks
- Rewriting instead of extracting
Getting help
If you want a review of your current design or a partner to build the first services, our microservices and Spring Boot architecture service is built for exactly that.