This is an addition to [[bind-apparmor]] and will automatically update bind when dhcp leases has been given out.

First check apparmor, mine looks like this:

<file>
# Last Modified: Mon Oct  6 20:46:31 2008
#include <tunables/global>
/usr/sbin/named {
  #include <abstractions/base>
  #include <abstractions/nameservice>
  #include <abstractions/nis>

  capability net_bind_service,
  capability setgid,
  capability setuid,
  capability sys_chroot,

  /usr/sbin/named mr,
  /var/lib/named/dev/random r,
  /var/lib/named/etc/127.0.0 r,
  /var/lib/named/etc/bind/named.conf r,
  /var/lib/named/etc/bind/named.conf.local r,
  /var/lib/named/etc/bind/rndc.key r,
  /var/lib/named/etc/localhost r,
  /var/lib/named/etc/localtime r,
  /var/lib/named/etc/named.run a,
  /var/lib/named/etc/root.hints r,
  /var/lib/named/etc/sites/example.com/** rw,
  /var/lib/named/etc/named.run rw,
  /var/lib/named/var/run/named.pid w,
}
</file>
It can be a really pain in the b*d but every time you make changes to your bind configuration (adding files and such), apparmor will block read/write access and prevent bind from working. Fortunately apparmor tells you what it has blocked so you can update your definition file and reload it.

Next is to generate a shared secret for intercommunication between dhcpd and bind:
<code>
sudo dnssec-keygen -r /dev/urandom -a HMAC-MD5 -b 128 -n USER DHCP_UPDATER
</code>

Grab the key from the file:
<code>
sudo cat Kdhcp_updater.*.private|grep Key
</code>

The output will be something like this:
<code>
Key: 9B7OkWhzwA+QZMenKqChVw==
</code>

Now do some changes to /etc/bind/named.conf.local and insert our key and allow dhcp updating:

<file>
key DHCP_UPDATER {
    algorithm HMAC-MD5.SIG-ALG.REG.INT;
    
        # Important: Replace this key with your generated key.
	# Also note that the key should be surrounded by quotes.
	secret "9B7OkWhzwA+QZMenKqChVw==";
};		

zone "example.com" IN {
	type master;
	file "sites/example.com/forward.zone";
	allow-transfer { 127.0.0.1; };
	allow-update { key DHCP_UPDATER; };    # This gives dhcp the update capabilities on the zone
	allow-query { any; };
	zone-statistics yes;
	notify no;
	also-notify {  };
};

zone "1.16.172.in-addr.arpa" {
	type master;
	file "sites/example.com/reverse.zone";
	allow-transfer { 127.0.0.1; };
	allow-update { key DHCP_UPDATER; };    # This gives dhcp the update capabilities on the reverse zone
	allow-query { any; };
	zone-statistics yes;
	notify no;
	also-notify {  };
};

</file>

Go into the dhcp server config file:
<code>
sudo nano  /etc/dhcp3/dhcpd.conf
</code>

<file>
ddns-update-style interim;
ignore client-updates;      # Overwrite client configured FQHNs
ddns-domainname "example.com.";
ddns-rev-domainname "in-addr.arpa.";

one-lease-per-client false;
allow bootp;
option T150 code 150 = string;

default-lease-time 600;
max-lease-time 7200;

log-facility local7;

key DHCP_UPDATER {
    algorithm HMAC-MD5.SIG-ALG.REG.INT;

    # Important: Replace this key with your generated key.
    # Also note that the key should be surrounded by quotes.
    secret "9B7OkWhzwA+QZMenKqChVw==";
};

zone example.com. {
  primary 127.0.0.1;
  key DHCP_UPDATER;
}

zone 1.16.172.in-addr.arpa. {
  primary 127.0.0.1;
  key DHCP_UPDATER;
}


subnet 172.16.1.0 netmask 255.255.255.0 {
    interface eth0;
    range 172.16.1.100 172.16.1.200;
    default-lease-time 6000;
    max-lease-time 7200;
    option domain-name "example.com";
    option subnet-mask 255.255.255.0;
    option routers 172.16.1.1;
    option domain-name-servers 172.16.1.1 , 193.162.153.164 , 194.239.134.83;
    option time-offset -3600;
    option ntp-servers dk.pool.ntp.org;
</file>

Now bounce the bind and dhcp services:
<code>
sudo /etc/init.d/bind9 restart
sudo /etc/init.d/dhcp3-server restart
</code>

Now whenever a new lease is dealt out the DNS records should be updated accordingly.

If you grain to a halt somewhere in the process a good place to look is in the syslog:
<code>
tail -f /var/log/syslog
</code>
I don't know why but I constantly end up being blocked by apparmor. So start looking for apparmor errors in the syslog when you head into trouble. 

//Source: http://lani78.wordpress.com/2008/08/12/dhcp-server-update-dns-records///