Spring Boot Actuator

# application.yml — Actuator configuration
management:
  endpoints:
    web:
      exposure:
        include: "health,info,metrics,loggers,env,prometheus"
        # use "*" to expose everything (not recommended in production)
      base-path: /actuator    # default; change to obscure from public

  endpoint:
    health:
      show-details: when-authorized  # show component details only to authenticated users
      show-components: always

  # Bind management endpoints to a separate internal port
  server:
    port: 8081  # expose actuator on internal port, block 8081 from public LB

# Kubernetes health probes — point to actuator
# spec.containers[].livenessProbe:
#   httpGet:
#     path: /actuator/health/liveness
#     port: 8081
# spec.containers[].readinessProbe:
#   httpGet:
#     path: /actuator/health/readiness
#     port: 8081

# application.yml — map built-in indicators to liveness/readiness groups
management:
  health:
    livenessState:
      enabled: true
    readinessState:
      enabled: true
  endpoint:
    health:
      group:
        liveness:
          include: "livenessState"
        readiness:
          include: "readinessState,db,redis"  # readiness includes DB + cache

// Custom HealthIndicator — reports health of a critical external dependency
@Component
public class ExternalApiHealthIndicator implements HealthIndicator {

    private final ExternalApiClient client;

    @Override
    public Health health() {
        try {
            client.ping();  // fast health-check call
            return Health.up()
                .withDetail("url", client.getBaseUrl())
                .build();
        } catch (Exception e) {
            return Health.down()
                .withDetail("error", e.getMessage())
                .build();
        }
    }
}

# See all loggers and their current levels
GET /actuator/loggers

# See a specific logger
GET /actuator/loggers/com.example.service

# Response:
# {"configuredLevel": "INFO", "effectiveLevel": "INFO"}

# Change level — POST with JSON body
curl -X POST http://localhost:8081/actuator/loggers/com.example.service \
  -H 'Content-Type: application/json' \
  -d '{"configuredLevel": "DEBUG"}'

# Reset to use parent level (inherits from root)
curl -X POST http://localhost:8081/actuator/loggers/com.example.service \
  -H 'Content-Type: application/json' \
  -d '{"configuredLevel": null}'

# Programmatic: change log level from application code (e.g., after a circuit breaker opens)
LoggingSystem loggingSystem = context.getBean(LoggingSystem.class);
loggingSystem.setLogLevel("com.example", LogLevel.DEBUG);