Update DNS

This Go program updates DNS records using the Cloudflare API. It supports both single domain updates and batch processing from a file.

New in v1.3.6: If you omit the IP address argument, the program will automatically detect your current public IP using nslookup myip.opendns.com resolver1.opendns.com.

• Go installed on your system.
• A Cloudflare account with an API token. The token should have permissions to edit DNS records.
• Set the environment variable CLOUDFLARE_API_KEY with your Cloudflare API token. The program supports four ways to invoke updates. The preferred form is a single domain/FQDN plus IP. The first argument may also be a path to a domains file for batch updates. Legacy three-argument form is still supported. You can now omit the IP address to auto-detect your public IP.

The program supports three ways to invoke updates. The preferred form is a single domain/FQDN plus IP. The first argument may also be a path to a domains file for batch updates. Legacy three-argument form is still supported.

1. Preferred single FQDN form (recommended): resolve zone automatically

update-dns <domain-or-fqdn> <new-ip>

• <domain-or-fqdn>: A fully-qualified domain name such as www.example.com, example.com, or a path to a domains file (see batch mode below). If a file with this name exists, it will be treated as a domains file.
• <new-ip>: The new IP address for the DNS record.

Behavior:

• If the first argument is a file path, the program runs in batch mode and treats the file as a list of domains to update.
• If the first argument is a FQDN, the program will automatically determine the Cloudflare zone by trying candidates from left-to-right (e.g., www.sub.example.com → tries www.sub.example.com, sub.example.com, example.com), using the first matching zone. The portion left of the found zone becomes the record name (or @ for the apex/root).

2. Batch mode (explicit file):

update-dns <domains-file> <new-ip>

You can also omit <new-ip> to auto-detect your public IP for all records in the file:

update-dns <domains-file>

• <domains-file>: Path to a text file containing domain/subdomain entries (one per line).
• <new-ip>: The new IP address for all DNS records.

3. Legacy form (still supported):

update-dns <domain> <subdomain> <new-ip>

• <domain>: The zone (e.g., example.com).
• <subdomain>: The record name to update (www or @ for the root).
• <new-ip>: The new IP address.

The domains file should contain one domain/subdomain per line. Examples:

www.example.com
api.example.com
mail.subdomain.example.com
.example.com

• Regular entries like subdomain.domain.com update that subdomain's A record.
• Entries starting with . (like .example.com) explicitly indicate the base/apex domain record should be updated.

1. The program initializes a connection to the Cloudflare API using the API token.
2. It retrieves the zone ID for the specified domain.
3. It lists all DNS records for the domain and finds the A record for the specified subdomain.
4. If the current IP address matches the new IP address, no changes are made.
5. If the IP addresses differ, the program updates the DNS record with the new IP address.
6. The program outputs a message indicating the IP address has been updated.

1. The program reads the domains file line by line.
2. For each domain entry, it parses the domain and subdomain components.
3. It processes each domain using the same logic as single domain mode.
4. Progress is tracked and reported, showing successful updates and any errors.
5. Individual domain failures don't stop the entire batch process.

• Single Mode: The program logs errors and exits if it encounters issues.
• Batch Mode: Individual domain errors are reported but don't stop processing of remaining domains. A summary is provided at the end showing success/failure counts.

go install github.com/jonfleming/update-dns@latest

Update a subdomain:

update-dns example.com www 192.0.2.1

Update the base domain:

update-dns example.com @ 192.0.2.1

Update multiple domains from a file:

update-dns domains.txt 192.0.2.1

With a domains.txt file containing:

www.example.com
api.example.com
.example.com
mail.anotherdomain.com

This will update:

• www.example.com → 192.0.2.1
• api.example.com → 192.0.2.1
• example.com (base domain) → 192.0.2.1
• mail.anotherdomain.com → 192.0.2.1