Amazon ECR Pull Through Cache (PTC)

What is ECR Pull Through Cache? Normally, to use an external image in the private environmet, we have to manually download the image and push it to ECR. With Pull Through Cache, we can simply pull the image using our ECR URL. AWS ECR automatically fetches the images from the upstream registry, caches it in our private registry and keeps it up to date with latest version. What are the public registries are supported? No Auth registries like AWS Public ECR, Kubernetes, Quay. Auth registries like D