gandi-dns-update

gandi-dns-update is a DNS updater for Gandi.net, which is ideal for use in container environments. It follows the principles of twelve-factor app. Whenever possible, networking timeouts are used to avoid hanging the application.

Principle of Operation

1. Do not rely on the system resolver, because DNS requests can be fed through a proxy.
2. Use Google DNS to lookup the NS of resolver1.opendns.com.
3. Determine the current dynamic IP:
   1. Use myip.opendns.com to lookup the current dynamic IP.
   2. Alternatively, if DOMAIN_IP is given, disable the dynamic lookup and use this IP address.
4. Use Google DNS to lookup the NS of the given domain (hosted with Gandi.net).
5. For each given dynamic item, lookup the (A) record in the Gandi NS and compare it against the current dynamic IP. Update it if it does not match.
6. Update DNS (A) record at Gandi, using the Gandi Live DNS API.

Network Timeouts (currently not configurable):

• DNS lookup: 15 seconds
• HTTP methods: 15 seconds

Commentary

I was in need for a tool like this for quite some time, and although there seem many projects like this one, most are either unmaintained, use either Python or Go (fill in arbitrary programming language here), using deprecated requirements, use configuration files, only use the system resolver, or do not use networking timeouts. At some point last year, I wrote a quick and dirty sketch in Python (using dns-lexicon) which worked (besides timeouts), but the container image had a size of 70 MiB. Running it in Kubernetes every 5 minutes 24/7 revealed that sometimes the job hangs because of a race conditions in the DNS resolver logic. This lead me to rewrite it from scratch in Rust, to learn something and to minimize the container image size. It uses trust-dns-resolver and reqwest. The final binary has 8 MiB and the container image has 9 MiB.

Limitations

• only IPv4 is supported
• only Gandi is supported

Building

nix build OR nix build .#gandi-dns-update-image OR cargo build --release

Container Images

Please find container images on GitHub Packages. An automatic build is configured using GitHub actions.

Configuration

The following environment variables are understood:

• GANDI_API_KEY :: Gandi Live DNS API key
• DOMAIN_IP :: Optionally disable current dynamic IP lookup and use this IP address
• DOMAIN_FQDN :: Domain to be managed, ending with a dot '.'
• DOMAIN_DYNAMIC_ITEMS :: List of entries within a domain to be updated. For example 'a' or 'a,b' will process the A records a.domain.tld and respectively b.domain.tld if domain.tld is given as DOMAIN_FQDN

NOTE: the domain must be fully qualified and needs to end with a dot '.'. The program will panic, if not full-filled.

Examples

Example usage as container:

docker run --rm \
       -e GANDI_API_KEY=your-api-key \
       -e DOMAIN_FQDN=domain.tld. -e DOMAIN_DYNAMIC_ITEMS=a,b,c \
       image-name:latest

Example usage with Cron:

*/5 * * * * /usr/bin/env -i GANDI_API_KEY=your-api-key DOMAIN_FQDN=domain.tld. DOMAIN_DYNAMIC_ITEMS=a,b,c /path/to/gandi-dns-update