Generate image thumbnails with AWS Lambda.
To load thumbnail for any image in the bucket use a prefix generated/<WIDTH>x<HEIGHT>. For example to load images/test.jpg image with maximum width set to 400 and maximum height set to 400 use generated/400x400/images/test.jpg path.
The solution is using generated prefix / folder, so that there can be two behaviors created in CloudFront distribution. One is public and anyone can request files from it. The second is private and signed URL is needed to get file.
This allows to return thumbnails with cache control header and user does not need to refetch them everytime. And in the same time it restricts to fetch original image without signed URL.
RestrictPathDimensions function checks if width and height combination in requested path is allowed. If not, it returns a redirect to the original image. This function is associated with public distribution.
ResizeImage function checks if resource allready exists. If yes, it returns original response. If not, it parses path, extracts width and height, generates resized image, stores it in generated folder and returns modified response.