In the event that you somehow need to rollback to the previous working version.
Codedeploy supports blue green deploy for ECS. That works great, but how do you manage the same sort of thing in S3?
Object Versioning https://docs.aws.amazon.com/AmazonS3/latest/dev/ObjectVersioning.html. You will need to have enabled versioning on the bucket already though. If you're going through CloudFront you can do this and create an invalidation.