Feature Toggle (aka Feature Flag)

// 설정값 관리
interface FeatureToggleProvider {
    fun isEnabled(key: String): Boolean
}

class FeatureToggleProviderImpl(private val repository: ToggleRepository) : FeatureToggleProvider {
    private val toggleConfigMap: AtomicReference<Map<String, ToggleConfiguration>> = AtomicReference(emptyMap())

    @Scheduled(fixedDelay = 5000)
    fun syncToggleConfiguration() {
        val newToggleConfigMap = repository.findAll()
            .associateBy({ it.key }, { this.parseConfig(it) })
        toggleConfigMap.set(newToggleConfigMap)
    }
    ...
}

// old, new feature 적용 로직
@Target(AnnotationTarget.FUNCTION)
@Retention(AnnotationRetention.RUNTIME)
annotation class FeatureToggle(
    val key: String,
    val fallbackMethod: String = "",
)

@Target(AnnotationTarget.FUNCTION)
@Retention(AnnotationRetention.RUNTIME)
annotation class FeatureToggleFallback

@Aspect
@Component
class FeatureToggleAspect(private val featureToggleProvider: FeatureToggleProvider) {
    private val fallbackExecutor = FeatureToggleFallbackExecutor()
    @Pointcut(value = "@within(featureToggle) || @annotation(featureToggle)", argNames = "featureToggle")
    fun matchAnnotatedClassOrMethod(featureToggle: FeatureToggle) {
    }
    @Around(value = "matchAnnotatedClassOrMethod(featureToggleAnnotation)", argNames = "proceedingJoinPoint, featureToggleAnnotation")
    fun featureToggleAroundAdvice(proceedingJoinPoint: ProceedingJoinPoint, featureToggleAnnotation: FeatureToggle): Any {
        ...
        // Toggle Point
        if (featureToggleProvider.isEnabled(key)) {
            return proceedingJoinPoint.proceed()
        }
        return fallbackExecutor.execute(proceedingJoinPoint, key, fallbackMethod)
    }
}

class MyFeatureProcessor {
    @FeatureToggle(key = "NEW_COOL_FEATURE", fallbackMethod = "oldFeature")
    fun newCoolFeature(): String {
        return "NewCoolFeature"
    }

    @FeatureToggleFallback
    fun oldFeature(): String {
        return "OldFeature"
    }
}