# Update DNS from a script when your IP changes

Keep a record such as `home.example.com` pointing at a connection whose address changes. A small script finds
your current address and changes the record only when it differs.

::: tip Using a router?
Most routers can update DNS themselves. InfraNest has a built-in **Dynamic IP** feature for that, with a link
your router calls. See [Dynamic IP on your router](https://infranest.io/docs/dynamic-ip-on-your-router). Use
this recipe when you want a script, for example on a Raspberry Pi or in a container.
:::

**Runnable code:** the code on this page, ready to clone and run, is in [`infranest-examples/examples/dynamic-dns`](https://github.com/InfraNest-Infrastructure-Organized/infranest-examples/tree/main/examples/dynamic-dns). CI runs it against the [sandbox](../sandbox.md).

## The token

Make a token with **DNS → Write** only, in the organization that holds the zone.

## Find the zone and the record

```sh
curl https://api.infranest.io/api/organizations/42/dns-zones \
  -H "Authorization: Bearer $INFRANEST_TOKEN" -H "Accept: application/json"
```

Note the zone's `id`, then list its A records:

```sh
curl "https://api.infranest.io/api/organizations/42/dns-zones/318/dns-records?type=A" \
  -H "Authorization: Bearer $INFRANEST_TOKEN" -H "Accept: application/json"
```

Note the `id` of the record you want to keep up to date.

## The script

```sh
#!/bin/sh
# Updates one A record to this machine's public IPv4 address, only when it changed.
set -eu
API=https://api.infranest.io/api/organizations/42/dns-zones/318/dns-records/9021

current=$(curl -fsS https://api.ipify.org)
stored=$(curl -fsS "$API" -H "Authorization: Bearer $INFRANEST_TOKEN" -H "Accept: application/json" | jq -r .value)

if [ "$current" != "$stored" ]; then
  curl -fsS -X PUT "$API" \
    -H "Authorization: Bearer $INFRANEST_TOKEN" \
    -H "Content-Type: application/json" \
    -d "{\"value\":\"$current\",\"ttl\":300}" > /dev/null
  echo "Updated to $current"
fi
```

Run it every five minutes, for example with cron: `*/5 * * * * /usr/local/bin/update-dns.sh`.

- **A short TTL** (300 seconds here) makes the new address take effect quickly. The minimum is 60.
- **Only changed addresses are sent**, so the script stays well inside the
  [rate limits](../tokens-and-scopes.md#rate-limits) and the zone's history shows real changes only.
- **To see what would change first**, add `?dry_run=1` to the `PUT`. See
  [Retries and dry runs](../retries-and-dry-runs.md).