Should we migrate our legacy Spring Boot monolith to a Microservices architecture using Java 21?

All answers to this question.

Migrating straight from a Java 8 monolith to microservices is often where projects go to die. I strongly recommend the "Modular Monolith" approach first. Use Java 21’s "Records" and "Modules" to enforce strict boundaries within your single codebase. This allows you to clean up your domain logic without the operational tax of Kubernetes, Service Meshes, and eventual consistency issues. Once your modules are truly decoupled and you find a specific part of the app that needs to scale independently, then extract it. Java 21’s performance boosts will likely make your monolith run 20% faster anyway just by upgrading the runtime.

   Answered 2024-07-10 by Patricia Garcia

That sounds like a huge undertaking! Are you planning on using Spring Modulith to help enforce those boundaries? It seems like a great way to validate your architecture before you start splitting things into separate jars. Do you think your DevOps team is ready to handle the observability requirements—like Jaeger or Zipkin—that microservices demand?

   Answered 2024-07-12 by Mark Robinson

• Mark, the observability point is huge. Many people forget that in a monolith, a stack trace is easy to follow. In microservices, you’re hunting through logs across five different pods. Using Spring Boot 3 with Micrometer Tracing makes this easier, but it’s still a steep learning curve. If Karen’s team is still on Java 8, they might find the jump to modern observability more challenging than the actual Java 21 syntax changes.

     Commented 2024-07-13 by Brian Hall

Don't underestimate the "Refactoring" phase. Moving to Java 21 gives you access to the foreign function API and better memory management, which helps even if you stay in a monolith.

   Answered 2024-07-15 by Thomas Scott

• Thomas is right. Just the G1 Garbage Collector improvements since Java 8 are worth the upgrade alone. It solves so many "stop-the-world" pause issues we used to have.

     Commented 2024-07-16 by Patricia Garcia