index.js

var dns = require('@google-cloud/dns')({
  projectId: 'my-project',
  keyFilename: './key.json'
});

/*
 *  Usage:
 *  https:[GoogleCloudURL]/dns2?host=foo.bar.com&ip=192.168.1.1&zone=my-zone
 *  all query parameters are required.
 *
 *  TTL and record type are hardcoded to 300 and 'A'.  This assumes that there
 *  will only be one type A record for the given name and TTL.
 *
 *  Security discussion:
 *  This uses service security key meaning that if the url and argument
 *  syntax are exposed, anyone can mess with your DNS server.  For me
 *  this was not an issue, since I am using this to provide dynamic DNS
 *  service to a pfSense security device - if the pfSense device is hacked
 *  then the exposer of dynamic DNS is the least of my concerns.
 *
 *  If you are using this code for a more public service, you probably want
 *  to use OAuth2 to secure it.
 *
 *  This: https://github.com/GoogleCloudPlatform/google-cloud-node considers
 *  the DNS interface to be an alpha quality API and could be easily broken
 *  with further development.
 */

exports.dns2 = function dns2 (req, res) { 
  var ip = req.query.ip;
  var host = req.query.host;
  var zone = req.query.zone;
  if (!ip || !host || !zone) {
    res.send('Sorry'); // intentionally vague for security reasons
    return;
  }
  try {
    var zone = dns.zone(zone);
  }
  catch (err) {
    // dns.zone doesn't throw many errors.  You may have to check the
    // console log to determine what went wrong here.
    res.send(err); 
    return;
  }

  var query = {
    name: host,
    type: 'A',
    maxResults: 1
  };
  zone.getRecords(query)
    .then((data) => {
      var oldRecord = data[0][0];
      var newRecord = zone.record('a', {
	"name": host,
	"data": ip,
	"ttl": 300
      });
      config = {
        add: newRecord,
	delete: oldRecord 
      };
      return zone.createChange(config).then( (data) => console.log('Updating ' + host + ': ' + config.delete.data + ' => ' + ip));
    })
    .catch((err) => console.log(err)); 
  res.send('done');
  return;
}; 


/*
 * This code works using googleapis rather than @google-cloud/dns
 * It's here as a reference.  I preferred the more readable version
 * above.
 *

var google = require('googleapis');
var dns = google.dns('v1');
var key = require('./key.json');

exports.dns1 = function dns1 (req, res) {
  var ip = req.query.ip;
  var host = req.query.host;
  if (!ip || !host) {
    res.send('Must include ip, host in query');
    return;
  }

  var jwtClient = new google.auth.JWT(
    key.client_email,
    null,
    key.private_key,
    ['https://www.googleapis.com/auth/cloud-platform'], // an array of auth scopes
    null
  );
  jwtClient.authorize(function (err, tokens) {
    if (err) {
      res.send('error1:' + err);
      return;
    }

    // Get the existing record for this name (required to change)
    var request = {
      project: 'my-project',	// Update
      managedZone: 'my-zone',	// Update
      auth: jwtClient,
      maxResults: 1,
      name: host,
      type: 'A',
    };
    var existingRecordSet;
    dns.resourceRecordSets.list(request).then(function (response) {
      if (response.rrsets.length >= 1) {
        existingRecordSet = response.rrsets[0];
      }

      var changes = {
        "kind": "dns#change",
        "additions": [
          {
            "kind": "dns#resourceRecordSet",
            "name": host,
            "type": "A",
            "ttl": 300,
            "rrdatas": [
              ip
            ]
          }
        ],
        "deletions": [
          existingRecordSet
        ]
      };

      request = {
        project: 'my-project',		// Update
        managedZone: 'project--zone',	// Update
        auth: jwtClient,
        resource: changes
      };
      dns.changes.create(request, function (err, response) {
        if (err) {
          res.send('error2:' + err);
          return;
        }
        if (existingRecordSet)
          console.log('Updated ' + host + ': ' + existingRecordSet.rrdatas[0] + ' => ' + ip);
        else
          console.log('Inserted ' + host + ': ' + ip);
        res.send(JSON.stringify(response));
      });
    }).catch(function(err) {
      res.send('error2:' + err);
      return;
    })
  });
};

 *
 */