The Container Image Manifest is a crucial component of Ocre containers, providing a comprehensive description of the container’s structure and contents. It serves as the blueprint that defines and references the three main elements of an Ocre container described in the Components section. The manifest ensures that all components can be correctly deployed and executed by the Ocre Runtime.

Ocre container images follow the Open Container Initiative (OCI) format where possible, with some modifications to support the needs of constrained, embedded devices. The manifest format is modeled after the OCI Image Manifest format and conforms to the Wasm OCI Artifact layout specifications. This structure ensures that all components of the container are properly defined, versioned, and can be efficiently managed in resource-constrained environments.

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Example

Here’s an example of an Ocre Container Image Manifest:

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.ocre.image.config.v1+json",
    "digest": "sha256:32b81b11f15ea9c198d59e143b2a5f15446b50b8954ce2e6cfab959988271c78",
    "size": 341
  },
  "layers": [
    {
      "mediaType": "application/vnd.ocre.image.v1.wasm",
      "digest": "sha256:6d61671e8d62f5e77ed054c2d3df4dc9b31e3c74fee7d478f3f2bbdc99a6f256",
      "size": 330
    },
    {
      "mediaType": "application/vnd.ocre.image.v1.blob",
      "digest": "sha256:201ef6570d2967b299cf5ab8f946f061d5db523c106bc90f72729693b798f431",
      "size": 709
    }
  ]
}

Configuration Parameters

The elements within the container configuration are defined as follows:

Required:

• schemaVersion (int): Image manifest schema version; per the OCI Image Spec this MUST be 2.
• mediaType (string): Required type of this manifest file. For Ocre containers, this MUST be application/vnd.ocre.image.manifest.v1+json.
• config (object): References the configuration object for this container image. Schema follows the OCI Content Descriptor schema. It has the following restrictions:
  • mediaType must be set to application/vnd.ocre.image.config.v1+json.
• layers (array): List of elements that comprise this container image. Each layer is a descriptor. One and only one layer MUST be of type application/vnd.ocre.image.layer.v1.wasm or application/vnd.ocre.image.layer.v1.wasm+aot.