Trivial bash Script to restart services in AWS

aws_restart.sh

#!/bin/bash
set -e

function usage {
   echo >&2 "Usage: $0 [ -e environment -n service_name -a action ]"
   exit 1
}

 while getopts ":n:e:a:" FLAG; do
   case $FLAG in    
  n) NAME=${OPTARG};;
  e) ENV=${OPTARG};;
  a) ACTION=${OPTARG};;
  [?]) usage;;
   esac
 done

 if [[ -z $NAME || -z $ENV || -z $ACTION ]]; then
   usage
 fi

 for fid in $(aws ec2 describe-instances --filters \
    "Name=tag:ServerEnv,Values=${ENV}" \
    "Name=tag:SubSystem,Values=${NAME}" \
    --query 'Reservations[*].Instances[*].PrivateIpAddress' --output text)
 do
  ssh -n $fid "sudo ${ACTION} ${NAME}; exit;"
 done