kotlin-app-config

name	kotlin-app-config
description	HOCON-basert konfigurasjon med PropertiesConfig singleton for Ktor batch-tjenester på NAIS (FSS)

Kotlin Application Configuration Skill

This skill describes the HOCON + PropertiesConfig singleton pattern used in this project. Config is loaded from layered HOCON files via Ktor's ApplicationConfig API.

PropertiesConfig Singleton

PropertiesConfig is a Kotlin object that holds all typed config sections as lazy properties. Call PropertiesConfig.load(config) once at startup; never re-initialize.

object PropertiesConfig {
    lateinit var config: ApplicationConfig
        private set

    val isLocal: Boolean
        get() = applicationProperties.isLocal

    val applicationProperties by lazy {
        config.property("application").getAs<ApplicationProperties>()
    }

    val postgresConfig by lazy {
        config.property("postgres").getAs<PostgresConfig>()
    }

    val sftpProperties by lazy {
        config.property("sftp").getAs<SftpProperties>()
    }

    val maskinportenClientProperties by lazy {
        config.property("maskinportenClient").getAs<MaskinportenClientConfig>()
    }

    val circuitBreakerConfig by lazy {
        config.property("circuitBreaker").getAs<CircuitBreakerConfig>()
    }

    val timerConfig by lazy {
        config.property("timer").getAs<TimerConfig>()
    }

    fun load(applicationConfig: ApplicationConfig) {
        if (!::config.isInitialized) {
            config = applicationConfig
        }
    }
}

Usage at Startup

private fun Application.module() {
    PropertiesConfig.load(environment.config.mergeWithEnv())

    val useAuthentication = PropertiesConfig.applicationProperties.useAuthentication

    if (!PropertiesConfig.isLocal) {
        PostgresDataSource.migrate()
    }

    if (!timerConfig.useTimer) return

    launchJob(skeService::handleNewKrav, timerConfig.schedulerIntervalPeriod)
}

Sub-files

• See hocon-layering.md for the layered HOCON pattern (mergeWithEnv()) and example HOCON config files.
• See config-classes.md for typed config section data classes (@Serializable) and testing configuration with MockK.

Benefits

• Single source of truth: All config in one singleton, no passing config objects around
• Lazy initialization: Config sections only parsed when first accessed
• Type safety: @Serializable data class properties with compile-time field names
• Environment layering: Local overrides without touching base config
• NAIS-native: Aligns with the HOCON layering convention used across NAV FSS services