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191 lines
8.1 KiB
Markdown
191 lines
8.1 KiB
Markdown
# OCI Image Index Specification
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The image index is a higher-level manifest which points to specific [image manifests](manifest.md), ideal for one or more platforms.
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While the use of an image index is OPTIONAL for image providers, image consumers SHOULD be prepared to process them.
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This section defines the `application/vnd.oci.image.index.v1+json` [media type](media-types.md).
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For the media type(s) that this document is compatible with, see the [matrix][matrix].
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## _Image Index_ Property Descriptions
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- **`schemaVersion`** *int*
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This REQUIRED property specifies the image manifest schema version.
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For this version of the specification, this MUST be `2` to ensure backward compatibility with older versions of Docker.
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The value of this field will not change.
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This field MAY be removed in a future version of the specification.
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- **`mediaType`** *string*
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This property SHOULD be used and [remain compatible][matrix] with earlier versions of this specification and with other similar external formats.
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When used, this field MUST contain the media type `application/vnd.oci.image.index.v1+json`.
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This field usage differs from the [descriptor](descriptor.md#properties) use of `mediaType`.
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- **`artifactType`** *string*
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This OPTIONAL property contains the type of an artifact when the manifest is used for an artifact.
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If defined, the value MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
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- **`manifests`** *array of objects*
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This REQUIRED property contains a list of [manifests](manifest.md) for specific platforms.
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While this property MUST be present, the size of the array MAY be zero.
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Each object in `manifests` includes a set of [descriptor properties](descriptor.md#properties) with the following additional properties and restrictions:
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- **`mediaType`** *string*
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This [descriptor property](descriptor.md#properties) has additional restrictions for `manifests`.
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Implementations MUST support at least the following media types:
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- [`application/vnd.oci.image.manifest.v1+json`](manifest.md)
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Also, implementations SHOULD support the following media types:
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- `application/vnd.oci.image.index.v1+json` (nested index)
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Image indexes concerned with portability SHOULD use one of the above media types.
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Future versions of the spec MAY use a different mediatype (i.e. a new versioned format).
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An encountered `mediaType` that is unknown to the implementation MUST NOT generate an error.
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- **`platform`** *object*
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This OPTIONAL property describes the minimum runtime requirements of the image.
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This property SHOULD be present if its target is platform-specific.
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- **`architecture`** *string*
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This REQUIRED property specifies the CPU architecture.
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Image indexes SHOULD use, and implementations SHOULD understand, values listed in the Go Language document for [`GOARCH`][go-environment2].
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- **`os`** *string*
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This REQUIRED property specifies the operating system.
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Image indexes SHOULD use, and implementations SHOULD understand, values listed in the Go Language document for [`GOOS`][go-environment2].
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- **`os.version`** *string*
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This OPTIONAL property specifies the version of the operating system targeted by the referenced blob.
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Implementations MAY refuse to use manifests where `os.version` is not known to work with the host OS version.
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Valid values are implementation-defined. e.g. `10.0.14393.1066` on `windows`.
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- **`os.features`** *array of strings*
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This OPTIONAL property specifies an array of strings, each specifying a mandatory OS feature.
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When `os` is `windows`, image indexes SHOULD use, and implementations SHOULD understand the following values:
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- `win32k`: image requires `win32k.sys` on the host (Note: `win32k.sys` is missing on Nano Server)
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When `os` is not `windows`, values are implementation-defined and SHOULD be submitted to this specification for standardization.
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- **`variant`** *string*
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This OPTIONAL property specifies the variant of the CPU.
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Image indexes SHOULD use, and implementations SHOULD understand, `variant` values listed in the [Platform Variants](#platform-variants) table.
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- **`features`** *array of strings*
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This property is RESERVED for future versions of the specification.
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If multiple manifests match a client or runtime's requirements, the first matching entry SHOULD be used.
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- **`subject`** *[descriptor](descriptor.md)*
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This OPTIONAL property specifies a [descriptor](descriptor.md) of another manifest.
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This value defines a weak association to a separate [Merkle Directed Acyclic Graph (DAG)][dag] structure, and is used by the [`referrers` API][referrers-api] to include this manifest in the list of responses for the subject digest.
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- **`annotations`** *string-string map*
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This OPTIONAL property contains arbitrary metadata for the image index.
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This OPTIONAL property MUST use the [annotation rules](annotations.md#rules).
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See [Pre-Defined Annotation Keys](annotations.md#pre-defined-annotation-keys).
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## Platform Variants
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When the variant of the CPU is not listed in the table, values are implementation-defined and SHOULD be submitted to this specification for standardization.
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These values SHOULD match (or be similar to) their analog listed in [the Go Language document][go-environment2].
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| ISA/ABI | `architecture` | `variant` | Go analog |
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|------------|----------------|-----------------------|-------------|
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| ARM 32-bit | `arm` | `v6`, `v7`, `v8` | `GOARM` |
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| ARM 64-bit | `arm64` | `v8`, `v8.1`, … | `GOARM64` |
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| POWER8+ | `ppc64le` | `power8`, `power9`, … | `GOPPC64` |
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| RISC-V | `riscv64` | `rva20u64`, … | `GORISCV64` |
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| x86-64 | `amd64` | `v1`, `v2`, `v3`, … | `GOAMD64` |
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## Example Image Index
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*Example showing a simple image index pointing to image manifests for two platforms:*
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```json,title=Image%20Index&mediatype=application/vnd.oci.image.index.v1%2Bjson
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{
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"schemaVersion": 2,
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"mediaType": "application/vnd.oci.image.index.v1+json",
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"manifests": [
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{
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"mediaType": "application/vnd.oci.image.manifest.v1+json",
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"size": 7143,
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"digest": "sha256:e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f",
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"platform": {
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"architecture": "ppc64le",
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"os": "linux"
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}
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},
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{
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"mediaType": "application/vnd.oci.image.manifest.v1+json",
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"size": 7682,
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"digest": "sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270",
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"platform": {
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"architecture": "amd64",
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"os": "linux"
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}
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}
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],
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"annotations": {
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"com.example.key1": "value1",
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"com.example.key2": "value2"
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}
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}
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```
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## Example Image Index with multiple media types
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*Example showing an image index pointing to manifests with multiple media types:*
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```json,title=Image%20Index&mediatype=application/vnd.oci.image.index.v1%2Bjson
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{
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"schemaVersion": 2,
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"mediaType": "application/vnd.oci.image.index.v1+json",
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"manifests": [
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{
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"mediaType": "application/vnd.oci.image.manifest.v1+json",
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"size": 7143,
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"digest": "sha256:e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f",
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"platform": {
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"architecture": "ppc64le",
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"os": "linux"
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}
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},
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{
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"mediaType": "application/vnd.oci.image.index.v1+json",
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"size": 7682,
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"digest": "sha256:601570aaff1b68a61eb9c85b8beca1644e698003e0cdb5bce960f193d265a8b7"
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}
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],
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"annotations": {
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"com.example.key1": "value1",
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"com.example.key2": "value2"
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}
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}
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```
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[dag]: https://en.wikipedia.org/wiki/Merkle_tree
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[go-environment2]: https://golang.org/doc/install/source#environment
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[iana]: https://www.iana.org/assignments/media-types/media-types.xhtml
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[matrix]: media-types.md#compatibility-matrix
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[referrers-api]: https://github.com/opencontainers/distribution-spec/blob/main/spec.md#listing-referrers
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[rfc6838]: https://tools.ietf.org/html/rfc6838
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[rfc6838-s4.2]: https://tools.ietf.org/html/rfc6838#section-4.2
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