I used the following commands to fix stopped hosted plesk websites (with nginx reverse proxy and Apache as webserver) after a system reboot
/usr/local/psa/admin/sbin/nginxmng --disable
/usr/local/psa/admin/sbin/httpdmng --reconfigure-all
Environment: Ubuntu 16.0.4; Plesk 17.0-17.5
/usr/local/psa/admin/sbin/nginxmng --enable
If your Plesk disables httpd/nginx after (security) updates (Please do not ask why Plesk has this problem on certain servers)
Create a script with following content and add it to your crontab (root):
#!/bin/bash
if curl -s --connect-timeout 3 --max-time 5 --head --request GET https://www.typo3blog.at/ | grep "200 OK" > /dev/null; then
exit 0
else
/usr/local/psa/admin/sbin/nginxmng --enable
systemctl restart nginx.service || true
fi