Create CloudFront invalidations when S3 origin changes

index.js

var aws = require('aws-sdk');
var cloudFront = new aws.CloudFront();

function getDistributionDomains(distribution) {
  return distribution.Origins.Items.map(function(origin) {
    return origin.DomainName;
  });
}

function findBucketDistributions(bucket, callback) {
  cloudFront.listDistributions(function(err, data) {
    if (err) {
      return callback(err);
    }
    
    var distributions = data.Items.filter(function(distribution) {
      return getDistributionDomains(distribution).some(function(domain) {
        return domain.indexOf(bucket) === 0;
      });
    });
    
    callback(null, distributions);
  });
}

function createInvalidation(distribution, callerReference, key, callback) {
  var path = '/' + key + '*';
  var params = {
    DistributionId: distribution.Id,
    InvalidationBatch: {
      CallerReference: callerReference,
      Paths: {
        Quantity: 1,
        Items: [path]
      }
    }
  };
  
  cloudFront.createInvalidation(params, function(err, data) {
    if (err) {
      return callback(err);
    }
    
    console.log('Invalidating "%s" in distribution %s (%s)', path, distribution.Id, getDistributionDomains(distribution).join(', '));
    
    callback(null, data.Invalidation);
  });
}

exports.handler = function(event, context) {
  var record = event.Records[0];
  var bucket = record.s3.bucket.name;
  var key = record.s3.object.key;
  var requestId = record.responseElements['x-amz-request-id'];
  
  findBucketDistributions(bucket, function(err, distributions) {
    var distribution = distributions[0];
    
    if (err || !distribution) {
      return context.done(err);
    }

    createInvalidation(distribution, requestId, key, context.done);
  });
};