* The scanner, 2020-10-29, Hacking Villa Diesbach
** Motivation
   - The purpose of cdist is to ensure systems are in a configured state
   - If systems reboot into a clean (think: netboot) state they are
     stuck in an unconfigured mode
   - We can either trigger *from* those machines
     - this is what cdist trigger is for
   - Or we can regulary *scan* for machines
     - This method does not need any modification to standard OS
** How it works
   - cdist scan uses the all nodes multicast group ff02::1
   - It sends a ping packet there in regular intervals
   - This even works in non-IPv6 networks, as all operating systems
     are IPv6 capable and usually IPv6 enabled by default
     - Link local is always accessible!
   - cdist scan receives an answer from all alive hosts
     - These results are stored in ~/.cdist/scan/${hostip}
     - We record the last_seen date  ~/.cdist/scan/${hostip}/last_seen
   - After a host is detected, cdist *can* try to configure it
     - It saves the result (+/- logging needs to be defined) in
       ~/.cdist/scan/${hostip}/{config, install}_result
     - If logging is saved: maybe in ~/.cdist/scan/${hostip}/{config, install}_log
     - Final naming TBD
** Benefits from the scanning approach
   - We know when a host is alive/dead
   - We can use standard OS w/o trigger customisation
     - Only requirement: we can ssh into it
     - Can make use f.i. of Alpine Linux w/ ssh keys feeding in
   - We can trigger regular reconfiguration
     - If alive && last_config_time > 1d -> reconfigure
   - Data can be exported to f.i. prometheus
     - Record when configured (successfully)
     - Record when seen
   - Enables configurations in stateless environments