Sometimes DNS servers just drop hostnames for a variety of reasons. Perhaps a customer forgets about a bill and their DNS records are wiped or there is an edit to a record, it’s not quite right and needs to be reverted and so on.
In an ideal world this would never happen but it does seem to every now and again. In most cases, this can be recovered but it can be a pain and also time consuming.
This is where DNS Historian comes in – an applicaton which monitors and records DNS changes. It also provides an http api to new hostnames can be added and existing ones can be queried. To find out more, check out: http://dns-historian.mage.me.uk/