4.5 Metrics & Observability

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Modern distributed architectures depend on the Three Pillars of Observability: Metrics, Logs, and Traces. Spring Boot integrates Micrometer as the vendor-neutral metrics facade (akin to SLF4J for metrics).

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1. Micrometer Core Meter Types

Meter Type	Characteristic	Real-World Application
Counter	Monotonically increasing value	Total HTTP requests, completed orders, error counts.
Gauge	Instantaneous snapshot value (can go up or down)	Current active thread count, database pool connections, queue size.
Timer	Measures both duration latency and count frequency	Endpoint execution time, DB query response times.
DistributionSummary	Tracks distribution of events not related to time	Payload sizes in bytes, batch processing sizes.

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2. Programmatic Metrics with MeterRegistry

@Service
public class CheckoutService {

    private final Counter orderSuccessCounter;
    private final Timer checkoutLatencyTimer;

    public CheckoutService(MeterRegistry registry) {
        this.orderSuccessCounter = Counter.builder("business.orders.placed")
                .description("Total successfully placed orders")
                .tag("region", "ap-south-1")
                .register(registry);

        this.checkoutLatencyTimer = Timer.builder("business.orders.checkout.time")
                .description("Time taken to process complete checkout flow")
                .publishPercentiles(0.5, 0.95, 0.99)
                .register(registry);
    }

    public OrderResult process(OrderRequest request) {
        return checkoutLatencyTimer.record(() -> {
            // Execution logic
            OrderResult result = executeCheckout(request);
            orderSuccessCounter.increment();
            return result;
        });
    }
}

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3. Prometheus & Distributed Tracing Integration

Prometheus Scraping

Add micrometer-registry-prometheus. Actuator automatically exposes /actuator/prometheus formatted for Prometheus scraper jobs:

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

Distributed Tracing in Spring Boot 3

Spring Boot 3 replaced Spring Cloud Sleuth with Micrometer Tracing supporting OpenTelemetry (OTel) and Brave/Zipkin:

<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-tracing-bridge-otel</artifactId>
</dependency>
<dependency>
    <groupId>io.opentelemetry</groupId>
    <artifactId>opentelemetry-exporter-otlp</artifactId>
</dependency>

With this dependency, every incoming HTTP request generates a traceId and spanId automatically propagated into logs and downstream network calls.