pre-traefik-reboot hook

Run before rebooting the Traefik container, when you call kamal traefik reboot.

If you have the hook disable the current server in an external load balancer and use the --rolling flag, you can use this for a zero-downtime Traefik reboot.

With a rolling reboot hook will be called once for each server, with KAMAL_HOSTS containing the current server. With a non-rolling reboot it will be called just once.

Use the post-traefik-reboot hook to re-enable the server.