[Unit]
 Description=APP Health check service
 After=network.target
 StartLimitIntervalSec=0
 
 [Service]
 Type=simple
 ExecStart=/bin/bash /path/to/shellscript.sh
 ExecStop=/bin/kill -15 $MAINPID
 Restart=always
 RestartSec=5s
 
 [Install]
 WantedBy=multi-user.target