lambda-image-dispatcher.js

exports.handler = function(event, context) {

  var sampleInput = {
    totalPhotos: 496,
    imagesPerLambda: 100,
    bucketName: 'sample-bucket',
    imageSizes: [{
      width: 600,
      height: 400,
      description: 'A medium thumbnail',
      prefix: 'thumb-',
      suffix: '-600x400'
    }, {
      width: 200,
      height: 100,
      description: 'A mini thumbnail',
      prefix: 'thumb-',
      suffix: '-200x100'
    }],
    sns: {
      channelName: 'test-channel'
    }
  };

  var numberOfChunks = Math.ceil(sampleInput.totalPhotos / sampleInput.imagesPerLambda);
  var chunks = _.range(0, numberOfChunks);

  var chunksBounds = _.map(chunks, function(chunk) {
    var from = chunk * sampleInput.imagesPerLambda + 1;
    var to = (chunk + 1) * sampleInput.imagesPerLambda > sampleInput.totalPhotos
      ? sampleInput.totalPhotos
      : (chunk + 1) * sampleInput.imagesPerLambda;
    
    return {
      from: from,
      to: to
    };
  });

  var lambdaInvokeOptions = _.map(chunksBounds, function(bounds) {
    return _.merge({}, bounds, {
      bucketName: sampleInput.bucketName,
      imageSizes: sampleInput.imageSizes
    });
  })
  
  // SNS is a simple wrapper around AWS SNS Node library
  var publishToChannel = SNS.publish(sampleInput.sns.channelName);
  _.each(lambdaInvokeOptions, publishToChannel);

  context.done(null, true);
}