I really don't like this.

Scenario: I have an out of date hosts file (days old). I want to run a critical task on all frontend machines. I run my task, but it does not run on a machine my colleague created yesterday. I don't realise this, so I now have missed running the critical task on one machine.

It would be "better" if Fabric checked the modified date on known_hosts_file and if it is older than a day, download it again. This would massively reduce the chances of this happening.