Actuator — 운영 중인 애플리케이션의 상태를 어떻게 확인할까

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

management:
  endpoints:
    web:
      exposure:
        include: health,info,metrics,prometheus  # 특정 엔드포인트만 노출
        # include: "*"  # 모든 엔드포인트 노출 (주의!)
        exclude: env,beans  # 특정 엔드포인트 제외

management:
  endpoint:
    health:
      show-details: always  # always | when_authorized | never
      show-components: always

{
  "status": "UP",
  "components": {
    "db": {
      "status": "UP",
      "details": {
        "database": "MySQL",
        "validationQuery": "isValid()"
      }
    },
    "diskSpace": {
      "status": "UP",
      "details": {
        "total": 499963174912,
        "free": 350000000000,
        "threshold": 10485760

      }
    },
    "redis": {
      "status": "UP",
      "details": {
        "version": "7.2.0"
      }
    }
  }
}

@Component
public class ExternalApiHealthIndicator implements HealthIndicator {

    private final RestClient restClient;

    public ExternalApiHealthIndicator(RestClient restClient) {
        this.restClient = restClient;
    }

    @Override
    public Health health() {
        try {
            ResponseEntity<Void> response = restClient.get()
                .uri("/health")
                .retrieve()
                .toBodilessEntity();

            if (response.getStatusCode().is2xxSuccessful()) {
                return Health.up()
                    .withDetail("status", "정상")
                    .build();
            }
            return Health.down()
                .withDetail("status", response.getStatusCode().value())
                .build();
        } catch (Exception e) {
            return Health.down()
                .withDetail("error", e.getMessage())
                .build();
        }
    }
}

management:
  endpoint:
    health:
      probes:
        enabled: true  # liveness, readiness 그룹 활성화
  health:
    livenessState:
      enabled: true
    readinessState:
      enabled: true

# Kubernetes deployment.yml
livenessProbe:
  httpGet:
    path: /actuator/health/liveness
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10
readinessProbe:
  httpGet:
    path: /actuator/health/readiness
    port: 8080
  initialDelaySeconds: 20
  periodSeconds: 5

GET /actuator/metrics
→ 사용 가능한 메트릭 이름 목록

GET /actuator/metrics/jvm.memory.used
→ JVM 메모리 사용량

GET /actuator/metrics/http.server.requests
→ HTTP 요청 통계

GET /actuator/metrics/http.server.requests?tag=uri:/api/users&tag=status:200
→ 특정 URI, 상태 코드로 필터링

@Service
public class OrderService {
    private final Counter orderCounter;
    private final Timer orderTimer;

    public OrderService(MeterRegistry registry) {
        this.orderCounter = Counter.builder("orders.created")
            .description("생성된 주문 수")
            .tag("type", "total")
            .register(registry);

        this.orderTimer = Timer.builder("orders.processing.time")
            .description("주문 처리 시간")
            .register(registry);
    }

    public Order createOrder(OrderRequest request) {
        return orderTimer.record(() -> {
            Order order = processOrder(request);
            orderCounter.increment();
            return order;
        });
    }
}

<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-registry-prometheus</artifactId>
</dependency>

management:
  endpoints:
    web:
      exposure:
        include: health,prometheus
  prometheus:
    metrics:
      export:
        enabled: true

@Configuration
public class ActuatorSecurityConfig {

    @Bean
    public SecurityFilterChain actuatorFilterChain(HttpSecurity http) throws Exception {
        return http
            .securityMatcher("/actuator/**")
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/actuator/health").permitAll()      // 헬스 체크는 공개
                .requestMatchers("/actuator/prometheus").permitAll()  // Prometheus 스크래핑
                .anyRequest().hasRole("ADMIN")                       // 나머지는 관리자만
            )
            .httpBasic(Customizer.withDefaults())
            .build();
    }
}

management:
  server:
    port: 9090  # Actuator를 다른 포트에서 운영
    address: 127.0.0.1  # 로컬에서만 접근 가능

# 현재 로그 레벨 확인
curl http://localhost:8080/actuator/loggers/com.example

# 로그 레벨 동적 변경 (서버 재시작 없이)
curl -X POST http://localhost:8080/actuator/loggers/com.example \
  -H "Content-Type: application/json" \
  -d '{"configuredLevel":"DEBUG"}'