Metrics with Micrometer and Prometheus

Micrometer is Spring Boot's metrics facade (like SLF4J for metrics). Boot auto-instruments HTTP requests, JVM, database pools and more; add micrometer-registry-prometheus to expose /actuator/prometheus. Record business metrics with Counter, Timer and DistributionSummary, or the Observation API (which also produces traces). Keep tag cardinality low.

@Service
class CheckoutMetrics {
    private final Counter ordersPlaced;
    private final Timer paymentTimer;

    CheckoutMetrics(MeterRegistry registry) {
        this.ordersPlaced = Counter.builder("shop.orders.placed").description("Orders placed").register(registry);
        this.paymentTimer = Timer.builder("shop.payment.duration").publishPercentileHistogram().register(registry);
    }

    PaymentResult timedCharge(Supplier<PaymentResult> charge) {
        PaymentResult result = paymentTimer.record(charge);
        ordersPlaced.increment();
        return result;
    }
}

Common pitfalls

• Tags with user IDs or order IDs (cardinality explosion).
• Only averages — enable histograms for percentiles.
• Measuring everything except business outcomes.

Key points

• Micrometer auto-instruments common components
• Custom business metrics
• Low-cardinality tags; histograms for percentiles

Further reading: Spring Boot: Metrics