[BE] Spring Actuator 관련 설정을 추가한다. (#941)

backend/bang-ggood/build.gradle

@@ -32,6 +32,10 @@ dependencies {
     implementation 'io.jsonwebtoken:jjwt-gson:0.11.2'
 
     annotationProcessor 'org.projectlombok:lombok'
+
+    implementation 'org.springframework.boot:spring-boot-starter-actuator'
+    implementation 'io.micrometer:micrometer-registry-prometheus'
+
     runtimeOnly 'com.h2database:h2'
 
     testImplementation 'org.springframework.boot:spring-boot-starter-test'

backend/bang-ggood/src/main/java/com/bang_ggood/global/config/MonitoringConfig.java

@@ -0,0 +1,24 @@
+package com.bang_ggood.global.config;
+
+import com.bang_ggood.global.repository.MonitoringChecklistRepository;
+import com.bang_ggood.global.repository.MonitoringUserRepository;
+import io.micrometer.core.instrument.MeterRegistry;
+import jakarta.annotation.PostConstruct;
+import lombok.RequiredArgsConstructor;
+import org.springframework.context.annotation.Configuration;
+
+@RequiredArgsConstructor
+@Configuration
+public class MonitoringConfig {
+
+    private final MeterRegistry meterRegistry;
+    private final MonitoringUserRepository monitoringUserRepository;
+    private final MonitoringChecklistRepository monitoringChecklistRepository;
+
+    @PostConstruct
+    public void initMetrics() {
+        meterRegistry.gauge("total.user.count", this, value -> monitoringUserRepository.countActiveUsers());
+        meterRegistry.gauge("total.checklist.count", this,
+                value -> monitoringChecklistRepository.countActiveChecklists());
+    }
+}

backend/bang-ggood/src/main/java/com/bang_ggood/global/repository/MonitoringChecklistRepository.java

@@ -0,0 +1,11 @@
+package com.bang_ggood.global.repository;
+
+import com.bang_ggood.checklist.domain.Checklist;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+
+public interface MonitoringChecklistRepository extends JpaRepository<Checklist, Long> {
+
+    @Query("SELECT COUNT(c) FROM Checklist c WHERE c.deleted = false")
+    long countActiveChecklists();
+}

backend/bang-ggood/src/main/java/com/bang_ggood/global/repository/MonitoringUserRepository.java

@@ -0,0 +1,11 @@
+package com.bang_ggood.global.repository;
+
+import com.bang_ggood.user.domain.User;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+
+public interface MonitoringUserRepository extends JpaRepository<User, Long> {
+
+    @Query("SELECT COUNT(u) FROM User u WHERE u.deleted = false")
+    long countActiveUsers();
+}