What is Micrometer and how do you expose metrics to Prometheus? Micrometer क्या है और आप metrics को Prometheus को कैसे expose करते हैं?

Micrometer is a metrics facade supporting multiple monitoring systems (Prometheus, Datadog, New Relic). Spring Boot Actuator uses Micrometer by default. Export metrics to Prometheus for visualization in Grafana dashboards.

// Micrometer Configuration
// pom.xml
<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-registry-prometheus</artifactId>
</dependency>

// application.yml
management:
  endpoints:
    web:
      exposure:
        include: prometheus
  metrics:
    tags:
      application: order-service
      environment: production

// Custom Metrics
@Service
public class OrderMetricsService {
    private final MeterRegistry meterRegistry;
    private final Counter ordersCreated;
    private final Timer orderProcessingTimer;
    
    public OrderMetricsService(MeterRegistry meterRegistry) {
        this.meterRegistry = meterRegistry;
        this.ordersCreated = Counter.builder('orders.total')
            .description('Total orders created')
            .tag('type', 'business')
            .register(meterRegistry);
        
        this.orderProcessingTimer = Timer.builder('order.processing')
            .description('Order processing time')
            .register(meterRegistry);
    }
    
    public void processOrder(Order order) {
        orderProcessingTimer.recordCallable(() -> {
            // Process order
            ordersCreated.increment();
            return null;
        });
    }
    
    public void recordInventoryLevel(int level) {
        meterRegistry.gauge('inventory.level', level);
    }
}

// Prometheus Configuration (docker-compose.yml)
version: '3.8'
services:
  app:
    image: app:latest
    ports:
      - '8080:8080'
  
  prometheus:
    image: prom/prometheus:latest
    ports:
      - '9090:9090'
    volumes:
      - ./prometheus.yml:/etc/prometheus/prometheus.yml
  
  grafana:
    image: grafana/grafana:latest
    ports:
      - '3000:3000'
    environment:
      - GF_SECURITY_ADMIN_PASSWORD=admin

// prometheus.yml
global:
  scrape_interval: 15s
scrape_configs:
  - job_name: 'spring-boot-app'
    static_configs:
      - targets: ['localhost:8080']
    metrics_path: '/actuator/prometheus'

// Grafana Queries
// Total orders: sum(orders_total)
// Order processing rate: rate(order_processing_seconds_sum[5m])
// P95 latency: histogram_quantile(0.95, order_processing_seconds)

// Key Micrometer Metrics:
// 1. Counter - incrementing metric
// 2. Timer - timing operations
// 3. Gauge - current value
// 4. Distribution Summary - distribution of values