Linode Dynamic DNS

linode-update-dns.sh

#!/bin/bash

# Updates Linode DNS records to the host's external IP, if the record differs.
#   * Depends on curl(1) and jq(1).
#   * Requires API key with read/write Domain permission.
#   * Presumes IPv4 (A record).
#
# Author: jkiv (https://github.com/jkiv)
#

# Linode Configuration
LINODE_API_TOKEN='<api_token>'
LINODE_DOMAIN_ID='<domain_id>'
LINODE_DOMAIN_RECORD_IDS=('<record_id_1>' '<record_id_2>')

# Get Current IP (uses opendns.com)
CURRENT_IP=$(dig @resolver4.opendns.com myip.opendns.com +short)

# Update each record for given domain
for RECORD_ID in ${LINODE_DOMAIN_RECORD_IDS[@]}; do
    # Grab current state of DNS record
    CURRENT_RECORD=$(\
        curl -s \
             -H "Authorization: Bearer ${LINODE_API_TOKEN}" \
             -X GET "https://api.linode.com/v4/domains/${LINODE_DOMAIN_ID}/records/${RECORD_ID}"\
    )
    
    RECORD_IP=$(echo "${CURRENT_RECORD}" | jq -r .target)
    RECORD_NAME=$(echo "${CURRENT_RECORD}" | jq -r .name)

    # Only update if IP address has changed
    if [ "${RECORD_IP}" != "${CURRENT_IP}" ]; then
        echo "Updating '${RECORD_NAME}' (${RECORD_ID}): ${RECORD_IP} -> ${CURRENT_IP}"
    
        # Update target field 
        CURRENT_RECORD=$(echo "${CURRENT_RECORD}" | jq '. | .target="[remote_addr]"')
    
        # Push update to Linode
        curl -s \
    	     -H "Content-Type: application/json" \
    	     -H "Authorization: Bearer ${LINODE_API_TOKEN}" \
    	     -X PUT -d "${CURRENT_RECORD}"\
    	     "https://api.linode.com/v4/domains/${LINODE_DOMAIN_ID}/records/${RECORD_ID}" | jq .
    fi
done