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README.md

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+# DNS Updater
+
+A small CLI that updates existing A records on supported DNS providers to match the current IP of your machine (either its public “WAN” IP or the IP of a local network interface).
+
+Runs once and exits — ideal to schedule with cron or a systemd timer.
+
+## Features
+- Update existing A records on multiple providers in one run
+- Providers: DigitalOcean, Vultr
+- Public IP lookup via pluggable services (ipecho, jsonip, etc.)
+- Resolve IP from a local interface (e.g., `eth0`)
+- Skips updates when the record is already up-to-date
+- Structured, human-readable logging
+
+## How It Works
+- Loads the YAML config and registers DNS providers.
+- Selects the configured public IP lookup service.
+- Iterates `updates` and, for each record:
+  - Resolves the target IP from `wan` (public IP) or a local interface name.
+  - Looks up the existing record by name on the provider.
+  - Updates the record only if the IP changed.
+
+Only A records are listed/updated; records must already exist.
+
+## Install
+- Requirements: Go 1.23+ (module toolchain sets `go1.24.1`).
+
+Build with Makefile:
+
+```
+make build
+```
+
+Or directly with Go:
+
+```
+go build -v -o build/dnsupdater cmd/dnsupdater/main.go
+```
+
+## Configuration
+See `config.example.yml` for a full example. Create your own `config.yml` alongside the binary (or pass `-config`):
+
+```yaml
+services:
+  IPLookup: ipecho   # one of: ipecho, jsonip, ifconfig.me, ip.me, icanhazip
+
+providers:
+  digitalocean:
+    token: <YOUR_DO_TOKEN>
+  vultr:
+    token: <YOUR_VULTR_TOKEN>
+
+updates:
+  digitalocean:
+    domain1.com:
+      www: wan        # use public IP
+      app: eth0       # use IP from local interface
+    domain2.com:
+      www: wan
+  vultr:
+    example.com:
+      www: wan
+```
+
+- `services.IPLookup`: public IP lookup backend. Supported values: `ipecho`, `jsonip`, `ifconfig.me`, `ip.me`, `icanhazip`.
+- `providers`: map of provider name to credentials. Current providers: `digitalocean`, `vultr`.
+- `updates`: which domains/records to update per provider.
+  - Value must be either `wan` (public IP) or a local interface name (e.g., `eth0`).
+
+Known limitation: literal IPv4 strings in `updates` (e.g., `84.24.254.21`) are not interpreted as IPs and will fail; use `wan` or an interface name instead.
+
+## Usage
+
+```
+./build/dnsupdater -config ./config.yml     # run once
+./build/dnsupdater -v                       # print version
+```
+
+Logs are written to stderr in a readable format.
+
+### Scheduling
+- Cron: `*/5 * * * * /path/to/dnsupdater -config /path/to/config.yml >/dev/null 2>&1`
+- systemd (example): create a service and timer that invoke the binary every few minutes.
+
+## Testing
+
+```
+make test
+```
+
+## Provider Notes
+- DigitalOcean: updates existing A records via the Domains API.
+- Vultr: updates existing A records via the DNS API.
+- Records must already exist; creation is not implemented.
+
+## Troubleshooting
+- “Invalid DNS service”: the name under `updates:` doesn’t match a configured provider.
+- “Failed to fetch ip”: `wan` lookup failed or the local interface name is wrong.
+- No change: when the on-file IP matches the resolved IP, the tool logs success without making an API call.
+
+## License
+AGPL-3.0-only. See `LICENSE`.
+