kotlin-app-config

Kotlin Application Configuration Skill

This skill provides patterns for type-safe environment configuration using Kotlin sealed classes.

Sealed Class Configuration Pattern

sealed class Environment(
    val name: String,
    val databaseUrl: String,
    val kafkaBrokers: String,
    val azureAdIssuer: String
) {
    data object Local : Environment(
        name = "local",
        databaseUrl = "jdbc:postgresql://localhost:5432/myapp",
        kafkaBrokers = "localhost:9092",
        azureAdIssuer = "http://localhost:8080/azuread"
    )

    data class Dev(
        private val env: Map<String, String>
    ) : Environment(
        name = "dev",
        databaseUrl = env.getValue("DATABASE_URL"),
        kafkaBrokers = env.getValue("KAFKA_BROKERS"),
        azureAdIssuer = env.getValue("AZURE_OPENID_CONFIG_ISSUER")
    )

    data class Prod(
        private val env: Map<String, String>
    ) : Environment(
        name = "prod",
        databaseUrl = env.getValue("DATABASE_URL"),
        kafkaBrokers = env.getValue("KAFKA_BROKERS"),
        azureAdIssuer = env.getValue("AZURE_OPENID_CONFIG_ISSUER")
    )

    companion object {
        fun from(env: Map<String, String>): Environment {
            return when (env["NAIS_CLUSTER_NAME"]) {
                "dev-gcp" -> Dev(env)
                "prod-gcp" -> Prod(env)
                else -> Local
            }
        }
    }
}

Using Configuration

fun main() {
    val env = Environment.from(System.getenv())

    val dataSource = createDataSource(env.databaseUrl)
    val kafkaProducer = createKafkaProducer(env.kafkaBrokers)

    logger.info("Starting application in ${env.name} environment")
}

With Konfig Library

import com.natpryce.konfig.*

data class AppConfig(
    val database: DatabaseConfig,
    val kafka: KafkaConfig,
    val azure: AzureConfig
)

data class DatabaseConfig(
    val url: String
)
data class KafkaConfig(
    val brokers: String
)
data class AzureConfig(
    val issuer: String
)

val config = EnvironmentVariables()

val appConfig = AppConfig(
    database = DatabaseConfig(
        url = config.getOrNull(Key("DATABASE_URL", stringType))
            ?: "jdbc:postgresql://localhost:5432/myapp"
    ),
    kafka = KafkaConfig(
        brokers = config.getOrNull(Key("KAFKA_BROKERS", stringType))
            ?: "localhost:9092"
    ),
    azure = AzureConfig(
        issuer = config.getOrNull(Key("AZURE_OPENID_CONFIG_ISSUER", stringType))
            ?: "http://localhost:8080/azuread"
    )
)