Hydra's Packet Builders
with the exception of one, packet-t2a-2, which is not managed this way
All of the hydra builders on Packet are stateless, netbooted machines.
Every day, the images are rebuilt at https://buildkite.com/grahamc/packet-nix-builder from the latest stable release of NixOS.
Once the build has completed, each machine is rebooted one after another.
This boot process erases all of the disks and creates a single ZFS stripe across all of them. No state is preserved between boots.
On the hydra server, hydra-packet-importer queries Packet's API for machines with the hydra tag and adds them to the Hydra machines file. This happens every few minutes.
It is safe to, at any time, reboot any of the machines. When they come back up, they will have empty disks and no state, and will hopefully come up just fine.
