Get Azure endpoint server from DHCP client

It is more efficient and cross-distribution safe to use the hooks function
from dhclient to obtain the Azure endpoint server (DHCP option 245).

This is done by providing shell scritps that are called by the hooks
infrastructure of both dhclient and NetworkManager.  The hooks then
invoke 'cloud-init dhclient-hook' that maintains json data
with the dhclient options in
/run/cloud-init/dhclient.hooks/<interface>.json .

The azure helper then pulls the value from
/run/cloud-init/dhclient.hooks/<interface>.json file(s). If that file does
not exist or the value is not present, it will then fall back to the
original method of scraping the dhcp client lease file.

3 files changed, 30 insertions, 0 deletions

diff --git a/tools/hook-dhclient b/tools/hook-dhclient
new file mode 100755
index 00000000..d099979a
--- /dev/null
+++ b/tools/hook-dhclient
@@ -0,0 +1,9 @@
+#!/bin/sh
+# This script writes DHCP lease information into the cloud-init run directory
+# It is sourced, not executed.  For more information see dhclient-script(8).
+
+case "$reason" in
+   BOUND) cloud-init dhclient-hook up "$interface";;
+   DOWN|RELEASE|REBOOT|STOP|EXPIRE)
+      cloud-init dhclient-hook down "$interface";;
+esac
diff --git a/tools/hook-network-manager b/tools/hook-network-manager
new file mode 100755
index 00000000..447b134e
--- /dev/null
+++ b/tools/hook-network-manager
@@ -0,0 +1,9 @@
+#!/bin/sh
+# This script hooks into NetworkManager(8) via its scripts
+# arguments are 'interface-name' and 'action'
+#
+
+case "$1:$2" in
+   *:up) exec cloud-init dhclient-hook up "$1";;
+   *:down) exec cloud-init dhclient-hook down "$1";;
+esac
diff --git a/tools/hook-rhel.sh b/tools/hook-rhel.sh
new file mode 100755
index 00000000..5e963a89
--- /dev/null
+++ b/tools/hook-rhel.sh
@@ -0,0 +1,12 @@
+#!/bin/sh
+# Current versions of RHEL and CentOS do not honor the directory
+# /etc/dhcp/dhclient-exit-hooks.d so this file can be placed in
+# /etc/dhcp/dhclient.d instead
+
+hook-rhel_config(){
+    cloud-init dhclient-hook up "$interface"
+}
+
+hook-rhel_restore(){
+    cloud-init dhclient-hook down "$interface"
+}