poll.sh

#!/bin/bash
while true
do
cd ~/<REPO_FOLDER>
git fetch
LOCAL=$(git rev-parse HEAD)
REMOTE=$(git rev-parse @{u})
if [ $LOCAL != $REMOTE ]; then
  git pull origin <TARGET_BRANCH>
  docker-compose up --build -d
fi
sleep 60
done

nano ~/poll.sh

contents of ~/poll.sh file ; make sure you replace REPO_FOLDER, TARGET_BRANCH, WEBHOOK_SECRET and APPLICATION_URL

make it executable

chmod +x poll.sh

crontab -e
#add the following line:
@reboot sh /home/ubuntu/poll.sh

restart system

sudo reboot