Monit conf for a host/domain/site

site.mon

### example.tld
   check host example.tld with address www.example.tld
 
   # ICMP check
     if failed icmp type echo
        for 2 times within 2 cycles
        then alert

   # HTTP check
      if failed port 80 protocol http
        with http headers [Host: www.example.tld, Cache-Control: no-cache]
          and request / with content = "www.example.tld"
        then alert

   # HTTPS check
      if failed port 443 type tcpSSL protocol http
        with http headers [Host: www.example.tld, Cache-Control: no-cache]
          and request / with content = "www.example.tld"
        then alert

/etc/monit/conf.d/

host = just an unique name, not a real host
address = real URL

Varnish:
touch /var/www/example.tld/public_html/pong
nano /var/www/example.tld/public_html/pong
add what ever you have as content; here: www.example.tld
nano /etc/varnish/default.vcl
add:
if (req.url ~ "/pong") {
return (pass);
}
systemctl reload varnish
nano /etc/monit/conf.d/sites
change:
and request /pong with content = "www.example.tld"
systemctl restart monit

And now you can monitor downtime with Varnish.