Simple-env-config

Simple-env-config is a small, lightweight strongly typed configuration library for Scala biased towards Docker microservices that use environment variables for configuration following Twelve-Factor App principals.

While Simple-env-config is designed around system envrironment variables it is compatible with any input source where you can generate a Map[String, String].

Why use Simple-env-config

Other Scala configuration libraries promote some bad practices:

• Passing around untyped configuration files where config.get("Key") can result in runtime exceptions.
• Hard to reason about configuration values. Merging multiple files, JVM properties and system environment variables makes it hard to understand the final configuration values.
• With Docker and environment variables config files are used as a thin mapping essentially a thin mapping to sys.env which means essentially declaring config multiple times: application.conf

aws-api-key=${AWS_API_KEY}
aws-api-secret=${AWS_API_SECRET}

docker.compose

version: "3"

services:
  myservice:
    image: mymicroservice:latest
    environment:
      - AWS_API_KEY:some-value
      - AWS_API_SECRET:some-value

MyApp.scala

Config conf = ConfigFactory.load();
val apiKey = conf.getString("AWS_API_KEY"); // BOOM runtime exception if env variable not set

Simple-env-config solves some of these issues by:

• Safely loading config eagerly providing a NonEmptyList[ConfigError] \/ A where A is a validated real type.
• Clean error messages
• No duplicating config definitions to do sys.env
• Reporting of captured values
• Providing a simple set of combinators

Example usage:

case class Config(awsApiKey: String, awsSecret: String)

object Config {
  def load (ConfigReport, NonEmptyList[ConfigError] \/ Config) =
    (ConfigAction.read[String]("AWS_API_KEY") |@| 
    ConfigAction.read[String]("AWS_API_SECRET")(Config.apply _).disjunctioned(sys.env)
}

object MyApp extends Application {
  val (configReport, config) = Config.load
  
  config match {
    case -\/(errors) =>
      println(errors)
      sys.exit(1)
    case \/-(c) =>
      println(configReport.prettyPrint)
      ....
  }

}

ConfigReport contains all successfully read values and provides functions for printing them as shown above. prettyPrintMaskPasswords: String and prettyPrintWithMask(maskPredicate: String => Boolean): String allow masking of sensitive data.