JSON templating with Typesafe Config

build.sbt

lazy val deployProd = taskKey[Unit]("Deploy a job to prod")
lazy val deployQA = taskKey[Unit]("Deploy a job to qa")
lazy val jobConfig = settingKey[Config]("Job configuration")

// Environments endpoints are defined via Credentials where realm contains the env name.
val qa = Credentials(...)
val prod = Credentials(...)

// Task to fetch an existing JSON document, generate a new configuration
// using per-job overrides and then use the result to deploy a job.
def deployJobTo(credentials: Credentials) =
  Def.task {
    val server = Credentials.toDirect(credentials)
    val _ = (publish in Docker).value

    // HTTP client based on "org.scalaj" %% "scalaj-http" % "2.3.0"
    def http(path: String, transform: HttpRequest => HttpRequest = identity): String = {
      val request = Http(server.host + path)
        .auth(server.userName, server.passwd)
        .header("Content-Type", "application/json")
        .header("Accept", "application/json")
      transform(request).asString.throwError.body
    }

    // Render Typesafe config as JSON
    def toJson(config: ConfigObject): String = {
      val opts = ConfigRenderOptions.defaults.setJson(true).setOriginComments(false).setComments(false)
      config.render(opts)
    }

    // The job configuration with some defaults
    val buildConf = jobConfig.value.withFallback(ConfigFactory.parseString(s"""
      name = "${name.value}"
      docker.image = "${(dockerTarget in Docker).value}"
      docker.command = "/opt/docker/bin/${(packageName in Docker).value}"
      deploy.environment = "${credentials.realm}"
      """))

    // Fetch and parse the existing configuration
    val currentJson = http(s"/scheduler/jobs/search?name=${buildConf.getString("name")}")
    val currentConf = ConfigFactory.parseString(s"{ current = $currentJson }").getObjectList("current") match {
      case list if list.isEmpty => ConfigFactory.empty.root
      case list => list.get(0)
    }

    // Use a Typesafe Config as a template and resolve variables using our build config + defaults
    val nextConf = ConfigFactory.parseFile((baseDirectory in ThisBuild).value / "jobs/default.conf")
      .resolveWith(buildConf)
      .withFallback(currentConf)
    val json = toJson(nextConf.root)

    // Only deploy if something changed
    if (json == toJson(currentConf)) {
      streams.value.log.info(s"Job ${name.value} is up-to-date in (${server.realm}) ${server.host} ...")
      streams.value.log.info(json)
    } else {
      streams.value.log.info(s"Deploying ${name.value} to (${server.realm}) ${server.host} ...")
      streams.value.log.info(json)
      http("/scheduler/iso8601", _.postData(json))
      streams.value.log.info("Job deployed")
    }
  }

// Example use
val someJob = project
  .settings(
    jobConfig := ConfigFactory.parseFile(baseDirectory.value / "src/main/resources/application.conf").getConfig("job"),
    deployProd := deployDockerJobTo(prod).value,
    deployQA := deployDockerJobTo(qa).value
  )