Image Components

An Ocre container consists of the following three components:

Component	Description
oci-layout	OCI Layout file in JSON format. Specifies the version of the imageLayoutVersion in use. Ocre containers must set this value to 1.0.0
index.json	Image index file in JSON format. Serves as the entry point for the container image. Ocre containers will have one manifest entry with the mediaType of application/vnd.oci.image.manifest.v1+json which points to the Ocre artifact.
blobs/	Directory containing content-addressable blobs. Blobs are stored as files with the naming convention of <alg>/<encoded> which much match the digest format <alg>:<encoded>. Ocre containers support the SHA-256 algorithm only.

oci-layout

The oci-layout file identifies this as an Open Container Image Layout. Written in UTF-8 encoded JSON, it contains a single field imageLayoutVersion which must be set to 1.0.0 for Ocre containers. This file follows the application/vnd.oci.layout.header.v1+json media type specification as defined here.

An example of this file is as follows:

{
    "imageLayoutVersion": "1.0.0"
}

index.json

The index.json file serves as the entry point for the container image. Written in UTF-8 encoded JSON, it contains a single manifest entry pointing to the Ocre artifact, using the mediaType of application/vnd.oci.image.manifest.v1+json. This file follows the OCI Image Index Specification.

An example of this file is as follows:

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.index.v1+json",
  "manifests": [
    {
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "digest": "sha256:b11ba766595f3bf6b1db36019cb09decc88aca35ff44dc5ae70bd88d4f188be4",
      "size": 445
    }
  ]
}

This illustrates an index that provides a single reference to the Ocre container image manifest.

blobs/

The blobs directory contains all content-addressable components of the Ocre container. Files are stored using the format <alg>/<encoded>, matching their digest format <alg>:<encoded>. Currently, Ocre containers only support the SHA-256 algorithm for these digests.

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Learn More

Learn how these components are organized by reading about the Image Manifest, which defines the complete structure of an Ocre container.