* 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
** Sample output v2020-10-29
23:14] bridge:~% sudo  cdist scan -b -I wlan0 -vv
VERBOSE: cdist: version 6.8.0-36-g91d99bf0
VERBOSE: scan: Host fe80::21d:72ff:fe86:46b is alive
VERBOSE: scan: Host fe80::ce2d:e0ff:fed4:2611 is alive
VERBOSE: scan: Host fe80::21b:fcff:feee:f4c1 is alive
VERBOSE: scan: Host fe80::e2ff:f7ff:fe00:20e6 is alive
VERBOSE: scan: Host fe80::20d:b9ff:fe49:ac11 is alive
VERBOSE: scan: Host fe80::9e93:4eff:fe6c:c1f4 is alive
VERBOSE: scan: Host fe80::ce32:e5ff:fe79:7ea7 is alive
VERBOSE: scan: Host fe80::219:d2ff:feb2:2e12 is alive
VERBOSE: scan: Host fe80::d66d:6dff:fe33:e00 is alive
VERBOSE: scan: Host fe80::21b:fcff:feee:f446 is alive
VERBOSE: scan: Host fe80::21b:fcff:feee:f4b1 is alive
VERBOSE: scan: Host fe80::20d:b9ff:fe4c:547d is alive
VERBOSE: scan: Host fe80::bad8:12ff:fe65:313d is alive
VERBOSE: scan: Host fe80::42b0:34ff:fe6f:f6f0 is alive
VERBOSE: scan: Host fe80::ba69:f4ff:fec5:6041 is alive
VERBOSE: scan: Host fe80::f29f:c2ff:fe7c:275e is alive
VERBOSE: scan: Host fe80::ba69:f4ff:fec5:8db7 is alive
VERBOSE: scan: Host fe80::42b0:34ff:fe6f:f863 is alive
VERBOSE: scan: Host fe80::21b:fcff:feee:f4bc is alive
...
