How to update a dynamic DNS zone in Synology DSM with nsupdate directly, without going through the various web services.

ddns_nsupdate.sh

#!/bin/sh

# Copyright (c) 2014, Peder O. Klingenberg
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
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# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in
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#    distribution.
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
##########

# This is a script to allow direct use of nsupdate to update a dynamic
# DNS zone from Synology DSM.  Not supported or endorsed by Synology
# Inc.  Developed on DSM 5.0, no guarantees on earlier or later
# versions.  IPv4 only, because that's all I use.

# Instructions for use:
#
# Prerequisites:
# 1) Set up ssh access as root to your DiskStation.
# 2) Install the DNS Server package.  This provides the necessary
#    nsupdate binary and a convenient way to store keys.  You don't
#    need to set up any zones, and unless importing new keys, the
#    DNS server doesn't need to run.
#
# Setup (this is the tricky bit, requiring shell use and file
# editing):
# 1) Drop this script somewhere convenient on the DS, for instance
#    /volume1/DS-hacks/ddns_nsupdate.sh, and make sure it's executable.
# 2) Log on to the DS as root, and append the following to two files,
#    which should already exist: 
#      /etc.default/ddns_provider.conf and
#      /etc/ddns_provider.conf
#    (It doesn't seem like the latter matters, but it seems they are
#    equal originally, so I kept them equal).  Anyway, append this,
#    adjusting path as necessary:
#      [Direct NSUpdate]
#         modulepath=/volume1/DS-hacks/ddns_nsupdate.sh
#	  queryurl=Direct_NSupdate
#
# Use:
# 1) Import the key to use for updates to the Synology DNS Server
#    using the DNS Server GUI, tab "Keys", button "create" ->
#    "import".  This will give you a key of the same name as your
#    dynamic domain, with a trailing dot.
# 2) Go to Control Panel - section "External Access", tab "DDNS".
#    Click "Add".
# 3) "Direct NSUpdate" should now be a choice of service provider.
#    Choose it.
# 4) "Hostname" is your desired name in the dynamic zone.  Not a FQDN.
# 5) "Username/Email".  We repurpose this field for the name of the
#    dynamic zone.  So enter your zone here, no trailing dot.
# 6) Enter whatever.  We ignore it.
# 7) "External address" is fairly self-explanatory, and pre-filled in
#    my GUI.
# 8) Click "Test Connection" or "OK".  Status should flip to "Normal"
#    after a while, and your DNS server should now answer requests for
#    <yourhost>.<dynamic-domain>.  You're done.  If it says something
#    else, check your upstream logs and start debugging.

##########
## Code follows

# Arguments as specified in /etc.default/ddns_provider.conf:

username=$1
password=$2  # We ignore this.
hostname=$3
ip=$4

# But we instead use
domain=$username

keyfile=/volume1/@appstore/DNSServer/named/etc/key/$domain.

if [ ! -r $keyfile ]; then
    echo badauth
    exit 1
fi

/volume1/@appstore/DNSServer/bin/nsupdate -k $keyfile <<EOF
zone $domain
update delete ${hostname}.${domain}. A
update add ${hostname}.${domain}. 600 A $ip
send
EOF

rc=$?

if [ $rc != 0 ]; then
    echo 911
    exit 2
fi

echo good