It happened that ms-be1012 was deactivated from PuppetDB automatically after it has been with puppet disabled for 14 days due to a disk issue.
This is because we use the node-ttl setting:
https://github.com/wikimedia/puppet/blob/ddc661fb5304b49bc8b45f0f5bdb8804d294fc91/modules/puppetmaster/manifests/puppetdb.pp#L66
That deactivate the host after 14d: https://docs.puppet.com/puppetdb/2.3/configure.html#node-ttl
While we all agree that hosts shouldn't be with puppet disabled for longer time, I think that in any case hosts shouldn't disappear either from PuppetDB given that in turn this will remove it from Icinga, known hosts file, making it a ghost with the risk to loose track of it.
Thoughts?