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Serverless Image Handler Readme

The serverless-image-handler mono repository contains the source code and documentation for the image-handler and image-thumbs AWS Lambda functions.

Table of Contents

Architecture

Architecture

Image Handler

Overview

The Image-handler is a solution Image Handler is a serverless image processing project built with Node.js 18 and the Sharp library. It allows you to dynamically scale images on the fly and serves them through AWS Lambda, AWS CloudFront, and AWS S3.

It aws originally forked from aws-solutions/serverless-image-handler repository, but has been heavily modified to suit our needs.

Prerequisites

  • Node.js v20.x or later
  • Terraform
  • Make / npm
  • AWS credentials with sufficient permissions to read images from S3

Usage

To scale images dynamically on the fly, you can make HTTP requests to the AWS CloudFront distribution URL. The images are fetched from AWS S3, processed using Node.js 20 and Sharp / libvips, and then served through CloudFront.

Example URL:

https://images.t-online.de/4k_hdr.jpg

For more details see the Usage documentation.

Environment variables

The following environment variables are used by the image-handler:

Name Description
AUTO_WEBP Flag if the AUTO WEBP feature should be enabled
CORS_ENABLED Flag if CORS should be enabled
CORS_ORIGIN CORS origin.
SOURCE_BUCKETS S3 Bucket with source images

Building

To build the package run:

make FUNC=image-handler build

Testing

Run tests using the following Make command:

make npm/test

Infrastructure deployment

Deploy the infrastructure using Terraform with the following Make command:

make FUNC=image-handler tf

Special interest section

Useful links:

  • Image too large with default settings: 2023/02/JPCPt616git7/image.png

Ströer specific adaptations

The file name does not matter

The way we process our images does not depend on the file name. The part that copies the images from the CMS into our delivery bucket will rename all images to image.${extension}.

When rendering the image, the image-handler will always look for this filename, so it does not matter what the original file name was. e.g.

  • 2023/02/JPCPt616git7/seo-title.png will be served as image.png
  • 2023/02/JPCPt616git7/other-usage-different-title.png will be served as image.png

resulting in the same response.

Cropping coordinates format

  • the original solution introduced thumbor cropping in v6
  • we have implemented this feature in advance, but with a slightly different syntax:
    • The original solution uses crop=left,top,right,bottom
    • We use crop=left,top,width,height to be more consistent with the CMS

Expired Content

  • The original solution uses the Expires header to cache images in the browser
  • Our solution:
    • reduces the Cache-Control: max-age according to the Expires header to handle expired content
    • Also, once the Expires header is reached, the image-handler will return a http/410 (GONE) status code

Additional filter: thumbhash

  • /filters:thumbhash()/ will trigger a hash-based thumbnail generation. See https://evanw.github.io/thumbhash/
  • The image can be cropped prior to this filter, but will ultimately be resized to 100x100 pixel to generate an efficient thumbnail
  • The response will be base64 encoded binary that can be converted via Thumbhash.thumbHashToDataURL()

Next data workaround

Within the HTML markup resides the next-data attribute

Within this data structure there are some image URLs that are not directly intended to be rendered. Consider them as templates. Google (and other bots) will find and use this URL nonetheless. This image-handler will replace all calls that contain template variables /__WIDTH__x0/ with an actual size to mitigate this.

Removal of features not required

If required once more, they need to be pulled from the original repository:

  • Recognition and the corresponding code:
    • "Smart Crop" (aka face recognition)
    • Content Moderation (e.g. NSFW detection)
  • Watermarking/Overlaying
  • Secretsmanager and URL signing
  • Dynamic S3 bucket selection