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Image Flex

A robust, secure, and easily deployable image resizing service that scales, optimizes, and caches images on "the edge," on the fly, built on AWS Serverless technologies. Served by CloudFront via an Origin Access Identity. Executed on Lambda@Edge. Backed by S3. Protected by AWS WAF. Provisioned via CloudFormation. Built and deployed by the Serverless Application Model (SAM) CLI.

Image Flex system diagram

Resized images will be converted to WebP format if the image request includes a valid Accepts header with "webp" listed in its value.

The original inspiration for this application came from this AWS blog post I read a few years back. The article intended to provide a [semi-]working example, which was far from being suitable for a production environment.

IMPORTANT!

While Image-Flex allows you to indicate a region to use other than us-east-1, CloudFront requires us-east-1. Until I figure out a workaround, don't attempt to deploy in any region other than us-east-1.

Prerequisites

Note that this is a production-ready application, not a tutorial. This document assumes you have some working knowledge of AWS, CloudFormation and the Serverless Application Model (SAM), AWS Lambda, S3, Node.js, NPM, and JavaScript.

Requirements

  1. Node.js v12.x (this is the latest version supported by Lambda@Edge). It's recommended to use Node Version Manager, which allows one system to install and switch between multiple Node.js versions.
  2. An AWS account.
  3. The AWS CLI.
  4. The AWS SAM CLI.

Be sure to configure the AWS CLI:

$ aws configure

For detailed instructions on setting up the AWS CLI, read the official AWS CLI documentation.

Quickstart

Deploy the whole service in 2 commands! Run the setup and update NPM scripts, passing a name for your execution environment (see Setting the execution environment). For a detailed explanation of these commands, see the section Building and Deploying.

$ npm run setup -- dev
$ npm run update -- dev
  1. The setup NPM script will create the CloudFormation deployment bucket. You only need to run this command once per execution environment.
  2. The update NPM script will build, package, and deploy the application stack to CloudFormation using the AWS SAM CLI. When the script is finished, it will print an "Outputs" section that includes the "DistributionDomain," which is the URL for your CloudFront distribution (e.g., [Distro ID].cloudfront.net). Note this value for later, as it is how you will access the service.

These scripts optionally accept an argument to indicate the execution environment. If you don't set the execution environment, the default of "dev" will be used. For info on setting the execution environment, see Setting the execution environment.

Example:

$ npm run setup -- staging
$ npm run update -- staging

Usage

Using an Image Flex implementation is easy. Once the infrastructure has spun up, simply upload your raw, unoptimized images to the S3 bucket root. You can then access those files directly, or pass a w (width) query string parameter to fetch a resized and optimized copy, which also gets stored in the S3 bucket and cached in CloudFront.

Example:

Suppose that you drop a 1600x900-pixel image named myimage.png into the created S3 bucket. You can now load this exact image in the browser via the distribution domain:

1600x900 pixels

https://[Distro ID].cloudfront.net/myimage.png

Using this full-resolution, unoptimized image would have negative performance impacts.

Resizing your images

w parameter

Now suppose that you want to load that image at 400 pixels width, maintaining the aspect ratio. It's as easy as adding the ?w=400 query string parameter.

400x225 pixels

https://[Distro ID].cloudfront.net/myimage.png?w=400

This will return a resized and optimized image (WebP, if supported by the browser).

h parameter

You can also add an h query string parameter to set the height. Note that changing the aspect ratio will clip the image (like object-fit: cover in CSS), not stretch or squash the image.

400x400 pixels, clipped

https://[Distro ID].cloudfront.net/myimage.png?w=400&h=400

How It Works

The fully actioned (built, packaged, and deployed) SAM template will result in a CloudFormation stack of resources being created across numerous AWS services (see the following table).

Any named resources will have the name prepended with the name of the stack, which itself is assembled from the application (image-flex), your AWS account ID, and the execution environment ("dev" by default). Example stack name: image-flex-412342973409-prod Example S3 bucket name: image-flex-412342973409-prod-images

Resource Type Resource Name Description
AWS WAF Web ACL [Stack Name]-WebAcl Defends the application from common web exploits by enforcing various access rules. This application implements AWS's Core Rule Set.
CloudFront Distribution N/A Content Delivery Network (CDN) to cache images at locations closest to users.
Logging S3 Bucket [Stack Name]-cflogs Stores the compressed CloudFront logs.
Hosting S3 Bucket [Stack Name]-images Serves as the CloudFront origin, storing the original image assets in the root, and resized image assets within subdirectories by width.
Origin Access Identity N/A Restricts direct access to the S3 bucket content, only allowing the CloudFront distribution to read and serve the image files.
Viewer Request Lambda@Edge [Stack Name]-UriToS3Key Responds to the "viewer request" CloudFront trigger, and will reformat the requested URI into a valid S3 key expected by the S3 bucket. Example: /image.png?w=300 => /300/image.webp
Origin Response Lambda@Edge [Stack Name]-GetOrCreateImage Responds to the "origin response" CloudFront trigger, and:
  1. If the requested image in the requested size is found, return it.
  2. Otherwise, if the requested image in the requested size is not found, attempt to create an image in the requested size from the base image.
  3. Otherwise, if the base image is not found, return HTTP status 404: Not Found.

Building and Deploying

The following NPM scripts are available:

  1. setup
  2. build
  3. package
  4. deploy
  5. update

Each NPM script calls a shell script of the same name in the /bin directory.

ℹ️ Setting the execution environment

These scripts (except for build) all run within the context of an execution environment (e.g., dev, staging, prod, etc.). This will be appended to the name of your Image Flex-based application in CloudFormation.

There are 2 ways to set the execution environment. If you don't explicitly set it via one of these methods, the default environment "dev" will be used.

To set the execution environment:

  1. Via the IF_ENV environment variable.
  2. By passing the [-- env] argument when calling the NPM scripts.

Note that if you both set the IF_ENV environment variable and pass this argument via the command line, the command line argument will take priority.

via environment variable

You can set the execution environment for all scripts by setting the IF_ENV environment variable.

Example: For MacOS:

export IF_ENV=prod

For Windows (development is untested on Windows):

setx IF_ENV "prod"

and then run the scripts, affecting your "prod" environment without the command-line arguments

npm run setup
npm run update

via the command line

Alternately, the setup, package, deploy, and update scripts accept an optional command line argument to indicate the current execution environment (e.g., dev, staging, prod, etc.).

Examples:

  • $ npm run update -- dev
  • $ npm run update -- staging
  • $ npm run update -- prod
  • $ npm run update -- bills-test

NPM Scripts

1. Setup

$ npm run setup [-- env]

Creates the CloudFormation deployment S3 bucket. SAM/CloudFormation will upload packaged build artifacts to this bucket to later be deployed. You only need to run this command once per execution environment.

2. Update

$ npm run update [-- env]

A convenience script that runs npm run build, npm run package, and npm run deploy in order.

These are generally only called directly when debugging.

3. Build

$ npm run build

Installs and builds the dependencies for the GetOrCreateImage Lambda function using a Docker container built on the lambci/lambda:build-nodejs12.x Docker container image.

4. Package

$ npm run package [-- env]

Packages (zips) the functions and built dependencies, and uploads the artifacts to the deployment bucket.

5. Deploy

$ npm run deploy [-- env]

Deploys the application as defined by the SAM template, creating or updating the resources.

Linting

Linting is instrumented via ESLint using Standardx (JavaScript Standard Style). To execute linting, run the following:

npm run lint

Testing

Unit tests are instrumented via Jest.

npm run test

Make it fully production-ready

While these steps are in no way required, here are some recommendations for a rock-solid, production ready implementation.

1. Use a CNAME

In the SAM template, under the Distribution resource, you can uncomment the following lines to use a CNAME instead of the *.cloudfront.net distribution domain.

# Uncomment the next two lines to use a custom CNAME (must be configured in Route 53 or another DNS provider).
Aliases:
  - YOUR CNAME HERE

Be sure to replace YOUR CNAME HERE with your actual CNAME, and ensure that CNAME is created in Route 53 (or another DNS provider).

2. Add your own SSL certificate for HTTPS

By default, this application will use the default CloudFront certificate for SSL/TLS. However, if you configure an Alias per the instructions above, it is required that you use your own certificate for SSL/TLS. In the SAM template, under the Distribution resource, make the following changes to configure the distribution to use your own certificate stored in Certificate Manager.

Change...

ViewerCertificate:
  CloudFrontDefaultCertificate: true

To...

ViewerCertificate:
  CloudFrontDefaultCertificate: false
  AcmCertificateArn: YOUR CERTIFICATE MANAGER ARN HERE
  SslSupportMethod: "sni-only"

Be sure to replace YOUR CERTIFICATE MANAGER ARN HERE with the ARN of your certificate.

3. Customize your image conversion settings

Image Flex uses Sharp to resize, convert, and optimize images. When the image is converted to webp (via the Sharp.toFormat method), certain options can be set to effect the output quality of the resulting webp image. By default, Image Flex only sets the output quality percentage in the GetOrCreateImage Lambda function:

quality: 95

This results in a webp with a max quality of 95%.

See the official Sharp documentation to learn all options that may be set.

License

Copyright 2021-2023 Horace Nelson.

Available for free personal or commercial use only under Creative Commons: Attribution-ShareAlike license.