docker-nsupdate-ddns

This script pushes container/ip information from a Docker instance to a DNS server via the DNS update mechanism desribed in RFC 2136 (nsupdate). nsupdate is implemented by ISC Bind9.

Every REFRESH_INTERVAL seconds, it queries all the Docker containers on the local host, finds their IP and pushes it with the name to the DNS server.

Running

The script takes environment variables or a config file. A sample config file is provided in config.sample. The file name of the config file can be passed as argument, but defaults to config.

The names of the environment variables is the same as in the config file. Environment variables have precendence over the config file.

Environment variables

docker run -d \
   -e DOMAIN=int.mtak.nl \
   -e HOSTNAME_LABEL=nl.mtak.docker-bind-ddns.hostname \
   -e DEFAULT_NETWORK=10.100.0.192/26 \
   -e REFRESH_INTERVAL=5 \
   -e ONE_SHOT=True \
   -e NAMESERVER=10.100.0.11 \
   -e TSIG_NAME=dck1 \
   -e TSIG_KEY=SyYXDCJ4kIs3qhvI= \
   merijntjetak/docker-bind/ddns:latest

Config file

cat <<EOF >configfile
DOMAIN=int.mtak.nl
HOSTNAME_LABEL=nl.mtak.docker-bind-ddns.hostname
DEFAULT_NETWORK=10.100.0.192/26
REFRESH_INTERVAL=5
ONE_SHOT=True
NAMESERVER=10.100.0.11
TSIG_NAME=dck1
TSIG_KEY=SyYXDCJ4kIs3qhvI=
EOF

docker run -d \
  -v `pwd`/configfile:/configfile
  merijntjetak/docker-bind-ddns:latest /configfile

Configuration

DOMAIN - Sets the domain in which the records are created. Needs to match the Bind zone.
HOSTNAME_LABEL - Docker label to override the default record name with. Use with docker --label=nl.mtak.docker-bind-ddns.hostname=nginx to get nginx.int.mtak.nl
DEFAULT_NETWORK - Preferred network to find IP for, in case there are multiple networks
REFRESH_INTERVAL - Interval between updates
ONE_SHOT - Set to True for the script to update once and immediately quit (nice for debugging)
NAMESERVER - Nameserver to push updates to
TSIG_NAME - Name of the TSIG key
TSIG_KEY - TSIG-KEY

Bind9 integration

Generate a key

tsig-keygen clientname >/etc/bind/keys/clientname.key
Include keys in your Bind9 configuration

include "/etc/bind/keys/*";

Allow updates to your zone:

zone "int.mtak.nl" {
    type master;
    file "/etc/bind/db/int.mtak.nl.zone";
    update-policy {
            grant clientname zonesub ANY;
    };
};

Design

Requirements

Eventual redunancy (Bind9 zone transfers to secondary)
Support for multiple individual Docker servers
IPv6 support
Detect hostname in decreasing order of priority:
- label
- Container name
Forward-only
Clean up DNS (DNS is stateful but the script isn't, so there might be a mismatch)

Todo

Make event-driven with Ahab
Add tests

Alternatives

CoreDNS didn't fit the requirements, because zone transfers out of a CoreDNS server do not include the records from the coredns-dockerdiscovery plugin.

3.0 KiB Raw Blame History