I know there is a built in email delivery function that notifies node operators when their node becomes offline. But that notification is usually delayed from hours to even days. Is there any other recommended methods of getting notified as soon as node gets offline?
UptimeRobot
Local Zabbix или что-то аналогичное по вкусу
This makes no sense. Monitoring shall be external to your network.
И чтоб два раза не вставать—I use Uptime Kuma on Oracle instance, and monitor for https response AllHealthy.
Plus Pushover. Realtime notifications (5 minutes max in the free tier) if node changes to offline or unhealthy