Where to do the logging

Client
  ↓
Filter       → HTTP raw logging
  ↓
Interceptor  → Request-level logging
  ↓
Controller
  ↓
AOP @Around  → Business-level logging
  ↓
Service
  ↓
AOP @AfterThrowing  → Exception logging
  ↓
Repository

SLF4J + Loki Integration

Spring Boot App
   ↓
SLF4J API
   ↓
Logback
   ↓
Log File / Stdout
   ↓
Promtail
   ↓
Loki
   ↓
Grafana

SLF4J (Simple Logging Facade for Java)

• A logging abstraction, not a logging implementation.
• Defines common logging APIs, but the real logging is done by an underlying framework.
• Think of it as an interface:
  • Let code depend on one API
  • Can switch logging implementations easily