Synchronize Hetzner Cloud private network for k3os

70-hetzner-net-routes.rules

#/etc/udev/rules.d/70-hetzner-net-routes.rules

SUBSYSTEM=="net", KERNEL=="eth*", RUN+="/usr/lib/sync-hetzner-routes"

README.md

Synchronize Hetzner Cloud private networks for k3os

This simple script creates the required route to allow communication between node on private network on k3os, following how Hetzner does on Ubuntu/Centos machines.

WARN: https://github.com/mikefarah/yq must be installed in order to fetch network metadata from Hetzner API

sync-hetzner-routes.sh

#!/bin/sh
set -o nounset
set -o errexit

# UDEV shell script synchronizing network routes with Hetzner network 
# properties. It uses the Metadata Server to fetch information of private
# networks and add or remove routes according to the `udev` action and the
# modified net interface.
#
# WARN: it requires https://github.com/mikefarah/yq to parse and extract data 
#       from the Hetzner API.
#
# Example:
#   #/etc/udev/rules.d/70-hetzner-net-routes.rules
#   SUBSYSTEM=="net", KERNEL=="eth*", RUN+="/usr/lib/sync-hetzner-routes"
#

API_URL=http://169.254.169.254/hetzner/v1/metadata/private-networks
INTERFACE_WAIT_LIMIT=10

info()  { echo '[INFO] ' "$@"; }
warn()  { echo '[WARN] ' "$@" >&2; }
fatal() { echo '[ERROR] ' "$@" >&2; exit 1; }

fetch_metadata() {
  TMP_METADATA="$(mktemp)"
  curl -s "${API_URL}" > "${TMP_METADATA}"

  info "metadata downloaded to ${TMP_METADATA}"
}

fetch_interface_ip() {
  nretry=0
  until [ ${nretry} -ge ${INTERFACE_WAIT_LIMIT} ]; do
    interface_ip="$(ip -4 -o address show "${INTERFACE}" | awk '{print $4}' | cut -d'/' -f1)"
    if [ -n "${interface_ip}" ]; then return; fi

    warn "interface ${INTERFACE} doesn't have an IP... wait until $$INTERFACE_WAIT_LIMIT will be reached"
    nretry=$((nretry+1)) 
    sleep 1
  done

  fatal "failed to find \`${INTERFACE}\` IP: $$INTERFACE_WAIT_LIMIT reached"
}

add_route() {
  fetch_interface_ip
  fetch_metadata

  network=$(yq eval '.[] | select(.ip=="'"${interface_ip}"'") | .network' "${TMP_METADATA}")
  gateway=$(yq eval '.[] | select(.ip=="'"${interface_ip}"'") | .gateway' "${TMP_METADATA}")

  if [ -z "${network}" ]; then fatal "no network found on Hetzner API for interface \`${INTERFACE}\` (ip: ${interface_ip})"; fi
  if [ -z "${gateway}" ]; then fatal "no gateway found on Hetzner API for interface \`${INTERFACE}\` (ip: ${interface_ip})"; fi

  ip route add "${network}" via "${gateway}" dev "${INTERFACE}"
}

remove_route() {
  ip_route="$(ip route show | grep -E "dev ${INTERFACE} $")"
  if [ -z "${ip_route}" ]; then fatal "no route found for interface \`${INTERFACE}\`"; fi
  
  ip route del "${ip_route}"
}

case "${ACTION}" in
  "add") add_route;;
  "remove") remove_route;;
  *) warn "action \`${ACTION}\` not handled... ignored"
esac