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Serverless image resizing at any scale

Michael Wittig – 10 Dec 2015

Serverless image resize architecture

This post demonstrates how you can create a bunch of resized images right after uploading an image to S3. The solution requires no servers, is scalable and can be automatically deployed within minutes.

The solution makes use of two S3 buckets:

  • The bucket that contains the original images. Users upload images to this bucket. This bucket is suffixed with -original in the following example.
  • The bucket that contains the resized images. The bucket is suffixed with -resized in the following example.

When you upload an image to the -original bucket a Lambda function is executed. The Lambda function downloads the image from S3, creates multiple resized versions and uploads them to the -resized S3 bucket. As of now three resized copies are created for every upload to -original:

  • 150x fixed width, height is scaled as needed
  • 50x50 scale image best into box
  • x150 fixed height, width is scaled as needed

The following figure demonstrates the image resizing process in detail.

Image resizing process

You can find out how ImageMagick resize works or read on to deploy the solution.

Deploying the solution

WARNING This example assumes that you have installed and configured the AWS Command Line Interface

Clone this repository …

$ git clone git@github.com:AWSinAction/lambda.git
$ cd lambda/

or download and extract the zipped repository.

$ wget https://github.com/AWSinAction/lambda/archive/master.zip
$ unzip master.zip
$ cd lambda-master/

Create an S3 bucket for your Lambda code in the US East (N. Virginia, us-east-1) region and upload the lambda.zip file (replace $LambdaS3Bucket with a S3 bucket name e.g. lambda-michael).

WARNING This bucket has nothing to do with the resizing of images. It contains the zipped source code of the Lambda function.

export AWS_DEFAULT_REGION=us-east-1
$ aws s3 mb s3://$LambdaS3Bucket
$ aws s3 cp lambda.zip s3://$LambdaS3Bucket/lambda.zip

Create a CloudFormation stack (replace $ImageS3Bucket with a name for your image bucket e. g. image-michael, replace $LambdaS3Bucket with your Lambda code S3 bucket name).

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$ aws cloudformation create-stack --stack-name lambda-resize --template-body file://template.json --capabilities CAPABILITY_IAM --parameters ParameterKey=ImageS3Bucket,ParameterValue=$ImageS3Bucket ParameterKey=LambdaS3Bucket,ParameterValue=$LambdaS3Bucket

Wait until the stack is created (retry if you get CREATE_IN_PROGRESS this can take a few minutes).

$ aws cloudformation describe-stacks --stack-name lambda-resize --query Stacks[].StackStatus

You can now upload your first image to the -original S3 bucket (you can also use the web based Management Console if you prefer).

$ aws s3 cp path/to/image.png s3://$ImageS3Bucket-original/image.png

You will see the resized images in the -resized bucket (you can also use the web based Management Console if you prefer).

$ aws s3 ls s3://$ImageS3Bucket-resized
PRE 150x/
PRE 50x50/
PRE x150/

$ aws s3 ls s3://$ImageS3Bucket-resized/150x/

As you can see, for every size configuration a new “directory” was created.

What’s next?

From this point you can think about how to enable your users to upload files into the -original S3 bucket if your use cases requires user generated content. To allow uploads from your users you should think about a way to protect your -original bucket with IAM permissions. You could use the Security Token Service to achieve this.

You should use CloudFront in combination with the -resized bucket to serve the resized images to your end users. This will decrease the latency by pushing your content to one of the edge locations of the CloudFront CDN network.


Remove all files in the -original and -resized bucket.

$ aws s3 rm --recursive s3://$ImageS3Bucket-original
$ aws s3 rm --recursive s3://$ImageS3Bucket-resized

Delete the CloudFormation stack.

$ aws cloudformation delete-stack --stack-name lambda-resize

Delete Lambda code S3 bucket (replace $LambdaS3Bucket).

$ aws s3 rb --force s3://$LambdaS3Bucket

Customize the code

If you want to make changes to the code you need to create a new lambda code file (lambda.zip) and upload the new zip to S3. You can adjust the config.json file to adjust the size configurations.

$ npm install
$ ./bundle.sh
$ aws s3 cp lambda.zip s3://$LambdaS3Bucket/lambda.zip


AWS Lambda can respond to S3 events like a new file was uploaded. The Lambda function will download the original image from S3 to create new resized images. The resized images are then upload to S3 again. The Lambda solution in scalable and does not require any operational work.

This blog post has been translated into German: Serverless die Größe von Bildern anpassen.

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We launched the cloudonaut blog in 2015. Since then, we have published 365 articles, 67 podcast episodes, and 67 videos. It's all free and means a lot of work in our spare time. We enjoy sharing our AWS knowledge with you.

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