Docker Image Manifest V 2, Schema 2

Registry image manifests define the components that make up an image on a container registry (see section on container registries). The more common manifest format we’ll be working with is the Docker Image Manifest V2, Schema 2 (more simply, V2.2). There is also a V2, Schema 1 format that is commonly used but more complicated than V2.2 due to backwards-compatibility reasons against V1.

The V2.2 manifest format is a JSON blob with the following top-level fields:
schemaVersion - 2 in this case
mediaType - application/vnd.docker.distribution.manifest.v2+json
config - descriptor of container configuration blob

layers - list of descriptors of layer blobs, in the same order as the rootfs of the container configuration
Blob descriptors are JSON objects containing 3 fields:
mediaType - application/vnd.docker.container.image.v1+json for a container configuration or application/vnd.docker.image.rootfs.diff.tar.gzip for a layer
size - the size of the blob, in bytes
digest - the digest of the content

Here is an example of a V2.2 manifest format (for the Docker Hub busybox image):

  1. {
  2.   "schemaVersion": 2,
  3.   "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  4.   "config": {
  5.     "mediaType": "application/vnd.docker.container.image.v1+json",
  6.     "size": 1497,
  7.     "digest": "sha256:3a093384ac306cbac30b67f1585e12b30ab1a899374dabc3170b9bca246f1444"
  8.   },
  9.   "layers": [
  10.     {
  11.       "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
  12.       "size": 755724,
  13.       "digest": "sha256:57c14dd66db0390dbf6da578421c077f6de8e88edd0815b4caa94607ba5f4c09"
  14.     }
  15.   ]
  16. }

OCI Image Manifest

The OCI image format is essentially the same as the Docker V2.2 format, with a few differences.

mediaType - must be set to application/vnd.oci.image.manifest.v1+json
config.mediaType - must be set to application/vnd.oci.image.config.v1+json

Each object in layers must have mediaType be either application/vnd.oci.image.layer.v1.tar+gzip or application/vnd.oci.image.layer.v1.tar.
Source: https://containers.gitbook.io/build-containers-the-hard-way/#registry-format-oci-image-manifest