Advanced Monitoring & Observability in Spring Boot

@Configuration
public class MetricsConfig {
    @Bean
    MeterRegistry meterRegistry() {
        return new SimpleMeterRegistry();
    }

    @Bean
    TimedAspect timedAspect(MeterRegistry registry) {
        return new TimedAspect(registry);
    }

    @Bean
    CountedAspect countedAspect(MeterRegistry registry) {
        return new CountedAspect(registry);
    }
}

@Service
public class UserService {
    private final MeterRegistry registry;

    public UserService(MeterRegistry registry) {
        this.registry = registry;
    }

    @Timed(value = "user.creation", description = "Time taken to create user")
    public User createUser(User user) {
        Counter counter = registry.counter("user.created");
        User saved = userRepository.save(user);
        counter.increment();
        return saved;
    }
}

@Configuration
public class PrometheusConfig {
    @Bean
    PrometheusProperties prometheusProperties() {
        return new PrometheusProperties();
    }

    @Bean
    PrometheusMeterRegistry prometheusMeterRegistry() {
        return new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);
    }
}

// application.properties
management.endpoints.web.exposure.include=prometheus,health,info
management.endpoint.prometheus.enabled=true
management.metrics.tags.application=my-application

@Component
public class CustomMetrics {
    private final MeterRegistry registry;
    private final Gauge activeUsers;
    private final Counter failedLogins;

    public CustomMetrics(MeterRegistry registry) {
        this.registry = registry;
        
        this.activeUsers = Gauge.builder("users.active", 
            userService, this::getActiveUserCount)
            .description("Number of active users")
            .register(registry);

        this.failedLogins = Counter.builder("auth.failed")
            .description("Number of failed login attempts")
            .register(registry);
    }

    private double getActiveUserCount(UserService userService) {
        return userService.getActiveUserCount();
    }

    public void recordFailedLogin() {
        failedLogins.increment();
    }
}