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Duck DNS

Duckdns is a free public DNS service that provides you with a domain name you can update to match your dynamic IP-address.

This container automates the process to keep the duckdns.org domain updated when your IP-address changes.

Configuration

First, register an account, add your subdomain and get your token from http://www.duckdns.org/

Either edit ~/IOTstack/docker-compose.yml or create a file ~/IOTstack/docker-compose.override.yml. Place your Duckdns token and subdomain name (without .duckdns.org) there:

docker-compose.override.yml
version: '3.6'
services:
  duckdns:
    environment:
      TOKEN: your-duckdns-token
      SUBDOMAINS: subdomain

Observe that at least the initial update is successful:

$ cd ~/IOTstack
$ docker-compose up -d duckdns
$ docker-compose logs -f duckdns
...SNIP...
duckdns    | Sat May 21 11:01:00 UTC 2022: Your IP was updated
...SNIP...
(ctrl-c to stop following the log)

If there is a problem, check that the resulting effective configuration of 'duckdns:' looks OK: 

$ cd ~/IOTstack && docker-compose config

Domain name for the private IP

Example public/private IP:s and domains

flowchart
I([Internet])
G("Router\npublic IP: 52.85.51.71\nsubdomain.duckdns.org")
R(Raspberry pi\nprivate IP: 192.168.0.100\nprivate_subdomain.duckdns.org)
I --- |ISP| G --- |LAN| R

As a public DNS server, Duckdns is not meant to be used for private IPs. It's recommended that for resolving internal LAN IPs you use the Pi Hole container or run a dedicated DNS server.

That said, it's possible to update a Duckdns subdomain to your private LAN IP. This may be convenient if you have devices that don't support mDNS (.local) or don't want to run Pi-hole. This is especially useful if you can't assign a static IP to your RPi. No changes to your DNS resolver settings are needed.

First, as for the public subdomain, add the domain name to your Duckdns account by logging in from their homepage. Then add a PRIVATE_SUBDOMAINS variable indicating this subdomain:

version: '3.6'
services:
  duckdns:
    environment:
      TOKEN: ...
      SUBDOMAINS: ...
      PRIVATE_SUBDOMAINS: private_subdomain

References