This solution lets you dynamically modify images cached in Amazon CloudFront via S3 Object Lambda using Lambda@Edge. S3 Object Lambda eliminates the need to create and store derivative copies of your data or to run expensive proxies, all with no changes required to your applications. Amazon CloudFront caches the transformed copies at the edge, enabling low-latency delivery to users.

After deploying the AWS Cloud Development Kit (CDK) application in this repository, you will be able to store images in a private bucket and retrieve images with their EXIF data stripped using a public URL. To further demonstrate the capabilities of this solution, you can specify a query string in the public URL to retrieve only the EXIF data instead of the image.

• Solution Architecture
• CDK Architecture
  • Stacks
• Installation
  • Prerequisites
  • Setup
  • Bootstrap
  • Deployment
• Usage
• Uninstall
• References
• Security
• License

1. The user makes a request for an object via a public URL.
2. The request arrives at the nearest Amazon CloudFront edge location.
3. If the object is not in the edge cache, CloudFront would typically send an origin request to the object origin in order to retrieve, return and cache the object. In this case we have configured CloudFront to route the origin request through Lambda@Edge.
4. The Lambda@Edge function uses its execution role to sign the origin request, giving the request an authentication principal. The request is returned to CloudFront.
5. CloudFront sends the updated, signed request to the S3 Object Lambda Access Point in order to retrieve the transformed object.
6. The S3 Object Lambda Access Point requires all access be made by authenticated principals. It receives our modified, signed request.
7. Upon validating that our principal has S3 Object Lambda access permissions, S3 Object Lambda invokes its Lambda function.
8. The Lambda function uses the supporting S3 Access Point to read the original file from S3 and transforms the file.
9. The Lambda function writes the result back to S3 Object Lambda.
10. CloudFront returns the object to the consumer and caches the object at the edge. Subsequent requests for this object will return the cached version instead of invoking S3 Object Lambda. By default objects are cached for 24 hours.

While Lambda@Edge functions are replicated to edge locations, their source region must be in us-east-1. We do not want to limit our S3 bucket to the same region. As such, this CDK application creates multiple stacks, where the LambdaEdge stack will always be deployed in us-east-1.

Because we can't natively share resource outputs between regions, we use SSM parameters to store the Lambda@Edge function version ARN, to be consumed by the Cdn stack possibly in another region. For example, the Storage and Cdn stacks can be deployed in us-west-2, while the LambdaEdge stack remains in us-east-1. The Cdn stack will use a custom resource to read the SSM parameters from us-east-1 for the Lambda@Edge function version ARN (Lambda@Edge origin request config) and S3 Object Lambda Access Point (origin domain name).

• Private S3 bucket
• Lambda function with EXIF tools for S3 Object Lambda
• Supporting access point for S3 Object Lambda
• S3 Object Lambda access point

• Lambda Edge function in us-east-1
• SSM parameters in us-east-1:
  • <base stack name>/Edge-Origin-Request-Version-Arn

• CloudFront distribution with:
  • Default origin: S3 Object Lambda access point (read from SSM)
  • Cache policy: cache "showExif" query string and enable compression
  • Origin request policy: "showExif" query string only
  • Lambda@Edge origin request (created in LambdaEdge stack, version ARN read from SSM)

• Python 3.x
• git
• Docker
• An AWS account
• AWS CLI
• AWS CLI configured
• AWS CDK

Note: you can use AWS Cloud9 which fulfills all of the prerequisites above. You may have to update AWS CDK by running npm install -g aws-cdk --force.

First, clone the repository to a local working directory:

git clone https://github.com/aws-samples/amazon-s3-object-lambda-with-amazon-cloudfront

Navigate into the project directory:

cd amazon-s3-object-lambda-with-amazon-cloudfront

This project is set up like a standard Python project. The initialization process also creates a virtualenv within this project, stored under the .venv directory. To create the virtualenv it assumes that there is a python3 (or python for Windows) executable in your path with access to the venv package. If for any reason the automatic creation of the virtualenv fails, you can create the virtualenv manually.

To manually create a virtualenv on MacOS and Linux:

python3 -m venv .venv

After the init process completes and the virtualenv is created, you can use the following step to activate your virtualenv.

source .venv/bin/activate

If you are a Windows platform, you would activate the virtualenv like this:

.venv\Scripts\activate.bat

Once the virtualenv is activated, you can install the required dependencies.

pip install -r requirements.txt

Deploying AWS CDK apps into an AWS environment (a combination of an AWS account and region) requires that you provision resources the AWS CDK needs to perform the deployment. These resources include an Amazon S3 bucket for storing files and IAM roles that grant permissions needed to perform deployments. The process of provisioning these initial resources is called bootstrapping.

The LambdaEdge stack is required to be deployed in us-east-1 while the other stacks may be deployed in other regions. All regions where you plan to deploy this solution will need to be bootstrapped. If you have already done this or have deployed CDK apps in the target regions already, please move on to the next section.

To bootstrap your environment, run the following:

cdk bootstrap

Possible customizations include:

cdk bootstrap --profile <profile_name> aws://<account id>/<region 1> aws://<account id>/<region 2>

More information on bootstrapping can be found here.

This solution is made up of 3 stacks within a single CDK application. This requires the --all flag during CDK operations to interact with all stacks at once.

To deploy the CDK app with the default profile and region, run the following:

cdk deploy --all

To customize the AWS CLI profile or region, use the following:

cdk deploy --profile <profile_name> --region <region_name> --all

Note: the lambda-edge stack will always be deployed in the us-east-1 region.

To use the solution:

• Upload test images to the private storage bucket. Some test images have been provided in the images directory of this project. See below for instructions on finding the S3 bucket name.
• Navigate to the CloudFront URL with the file name attached, e.g. https://a1b2c3d4e5f6g7.cloudfront.net/test.jpg
  • This will return the image without any EXIF data.
• Append the query string ?showExif=true to the URL, e.g. https://a1b2c3d4e5f6g7.cloudfront.net/test.jpg?showExif=true
  • This will return the image's EXIF data in JSON format

S3 Bucket

• The bucket name will be displayed after CDK deploy is complete:

  Outputs:
  anon-s3ol-storage.s3bucket = anon-s3ol-storage-storagebucketa1b2c3d4-a1b2c3d4e5f6
  

• Alternatively, you can go to the console for AWS CloudFormation.
  • Select "anon-s3ol-storage"
  • Select the "Outputs" tab
  • The S3 Bucket name will be listed in the outputs list with t he s3bucket key

CloudFront URL

• The public-facing URL will be displayed in your terminal after CDK deploy is complete:

  Outputs:
  anon-s3ol-cdn.cf-domain = **a1b2c3d4e5f6g7.cloudfront.net**
  

• Alternatively, you can go to the console for AWS CloudFormation.
  • Select "anon-s3ol-cdn"
  • Select the "Outputs" tab
  • The S3 Bucket name will be listed in the outputs list with the cf-domain key

CloudFront replicates Lambda@Edge functions at the edge. These Lambda functions can only be deleted when all of the replicas have been deleted.

Prior to destroying the stack, the Lambda@Edge function must be disassociated from the CloudFront distribution:

1. Sign into the AWS Management Console and open the CloudFront console.
2. Select the distribution created by this app. Its description will mention anonymous S3 Object Lambda access.
3. Select the Behaviors tab.
4. Select the default behavior and choose Edit.
5. Scroll to the Function associations section and for Origin request, select No association.
6. Select Save changes.

Replicas are typically deleted within a few hours.

To remove all stacks in this app, run the following in the project directory:

cdk destroy --all

If you did not disassociate the Lambda@Edge function from the CloudFront distribution prior to running this command, the delete will fail when attempting to delete the lambda-edge stack. However, the CloudFront distribution (cdn stack) will have been deleted at this point. Simply wait for the Lambda@Edge function replicates to be removed from edge locations (up to a few hours), then run the delete command again.

See CONTRIBUTING for more information.

This library is licensed under the MIT-0 License. See the LICENSE file.