Dynamic DNS update using AWS Lightsail Domain API

update-dns.sh

#!/bin/bash

set -eo pipefail

DOMAIN=example.com
ENTRY=examplehost
#LINE_TOKEN=xxxxxx

get_ip() {
  curl -s 'https://api.ipify.org'
}

get_dns() {
  aws lightsail get-domain --domain-name=$DOMAIN |
  jq -r ".domain.domainEntries[] | select(.name == \"$ENTRY.$DOMAIN\") | .target"
}

get_id() {
  aws lightsail get-domain --domain-name=$DOMAIN |
  jq -r ".domain.domainEntries[] | select(.name == \"$ENTRY.$DOMAIN\") | .id"
}

update() {
  local ID=$1
  local IP=$2
  aws lightsail update-domain-entry --domain-name $DOMAIN --domain-entry id=$ID,name=$ENTRY.$DOMAIN,type=A,target=$IP
}

IP=`get_ip`
DNS=`get_dns`

if [ "$IP" != "$DNS" ]; then
  echo "Updating $ENTRY.$DOMAIN from $DNS to $IP"
  ID=`get_id`
  update $ID $IP

  ## Send a notification
  #curl -H "Authorization: Bearer $LINE_TOKEN" \
  #  -d message="$ENTRY.$DOMAIN changed IP to $IP" \
  #  https://notify-api.line.me/api/notify
fi