Dynamically configure Passenger based on current Dyno type

passenger_throttle.sh

#!/bin/bash
# http://stackoverflow.com/questions/24634958/programmatically-detect-heroku-dyno-size-at-run-time/24634959#24634959

function dyno_size() {
  case $(ulimit -u) in
    256)
      echo "1X"
      ;;
    512)
      echo "2X"
      ;;
    32768)
      echo "PX"
      ;;
    *)
      echo "unknown"
      ;;
  esac
}

case $(dyno_size) in
  1X)
    echo "--min-instances=1 --max-pool-size=1"
    ;;
  2X)
    echo "--min-instances=3 --max-pool-size=3"
    ;;
  PX)
    echo "--min-instances=12 --max-pool-size=12"
    ;;
  *)
    echo "--min-instances=1 --max-pool-size=1"
    ;;
esac