FailoveringService.scala

/**
  * Wraps two services in a new service which checks whether the {{primaryService}} is 
  * available and uses it when it is available. Otherwise, it will use the {{backupService}}.
  */
class FailoveringService[Req, Rep](primaryService: Service[Req, Rep],
                                   backupService: Service[Req, Rep])
  extends Service[Req, Rep] {
  
  override def apply(request: Req) =
    (if (primaryService.isAvailable) primaryService else backupService) (request)

  override def status = Status.best(primaryService.status, backupService.status)

}