How does Micrometer integrate with Spring Boot for metrics, and what backends can it export to?

Micrometer is a vendor-neutral metrics facade — conceptually similar to how SLF4J decouples application logging calls from a specific logging backend (Logback, Log4j2). Application code instruments metrics through Micrometer's API, and a separate, swappable registry determines which actual monitoring backend those metrics get exported to.

Auto-configuration: as soon as spring-boot-starter-actuator is on the classpath, Spring Boot automatically wires up Micrometer and starts capturing a substantial set of built-in metrics with zero extra code:

• HTTP request counts, latencies, and status-code breakdowns per endpoint (http.server.requests).
• JVM metrics — heap/non-heap memory usage, garbage collection pause counts/durations, thread counts.
• Data source connection pool metrics (active/idle connections, wait time) for HikariCP.
• Cache hit/miss rates, if a supported caching provider is in use.

Registering custom application metrics:

@Service
class OrderService {
    private final Counter ordersPlacedCounter;
    private final Timer orderProcessingTimer;

    OrderService(MeterRegistry registry) {
        this.ordersPlacedCounter = registry.counter("orders.placed");
        this.orderProcessingTimer = registry.timer("orders.processing.time");
    }

    void placeOrder(Order order) {
        orderProcessingTimer.record(() -> {
            // ... process the order ...
            ordersPlacedCounter.increment();
        });
    }
}

Exporting to a specific backend just means adding the corresponding registry dependency — the instrumentation code above never needs to change regardless of which backend is chosen:

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

This automatically exposes an additional endpoint, /actuator/prometheus, in the text-based exposition format Prometheus's scraper expects. Similar registry dependencies exist for Datadog, New Relic, CloudWatch, Graphite, InfluxDB, and many other monitoring platforms — the same underlying metrics, exported through whichever registry/registries are on the classpath, potentially to multiple backends simultaneously if more than one registry dependency is present.

Why the facade design matters: it lets application code (and, importantly, all of Spring Boot's own built-in auto-generated metrics) remain completely decoupled from any specific monitoring vendor — switching from, say, an on-prem Prometheus setup to a hosted Datadog account (a real, not-uncommon migration) requires only a dependency and configuration change, not rewriting instrumentation scattered throughout the codebase.