refactor: Merge Microservices Architecture into a Monolithic Application

[dennis9486]

Title

Merge Microservices Architecture into a Monolithic Application

Overview

Merge multiple existing microservices into a single monolithic application to simplify operations, accelerate development iterations, and reduce maintenance costs.
This change will keep a modular code structure (modules/packages) but unify the deployment process and database.
Cross-service network calls will be removed in the short term.

Goals

• Replace multiple microservice processes with a single deployable package (jar/docker).
• Preserve clear business module boundaries and layered architecture.
• Remove inter-service remote calls (Feign/RPC) and switch to internal method or library calls.
• Keep existing functionality and API behavior unchanged for external clients.

Task Checklist

• Define monolithic project structure: modules or corresponding package structure.
• Replace remote service calls with local method or shared library calls.
• Unify configuration: merge config centers or use profiles (while preserving runtime configurations).
• Merge database connections and data source strategies (resolve table prefix/namespace conflicts if needed).

Acceptance Criteria

• All existing features pass regression tests under monolithic deployment.
• External APIs remain unchanged or are migrated smoothly via a compatibility layer.
• The deployment package can be started with a single command; monitoring and logging work properly.
• Performance (latency, concurrency) meets business KPIs.

Risks & Considerations

• Monolithic deployment may increase single-instance resource usage and impact availability — HA strategy (replicas/load balancing) should be considered.
• Database table conflicts or transaction boundaries must be reviewed and migrated carefully.
• Keep code modular to allow future re-splitting into microservices if needed.