Operating System Images

IronCore uses Open Container Initiative (OCI) images as the standard format for operating system images. This allows for a consistent and portable way to manage and deploy operating systems across different environments. OCI images in IronCore are used both for virtual machine creation in the Infrastructure as a Service and in the Bare Metal Automation layers. IronCore OCI images should not be confused with container images, as they represent a full operating system rather than just a single application or service.

The core idea behind using OCI as a means to manage operating system images is to leverage any OCI compliant image registry, to publsish and share operating system images. This can be done by using a public registry or host your own private registry.

OCI Image Format

The IronCore OCI image format is specified in the OCI Image Specification. The specification defines how the image is structured, including the layers, configuration, and metadata required to run an operating system. The ironcore-image repository provides tools and utilities to create, manage, build and publish OCI images in IronCore. It is your go-to resource for understanding the specifics of the OCI image format used in IronCore.

Example OCI Image

An example of an OCI image in IronCore can be found below:

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.ironcore.image.artifacts.v1+json",
  "config": {
    "mediaType": "application/vnd.ironcore.image.config.v1+json",
    "digest": "sha256:configdigest1234abcd5678efgh9012ijkl3456mnop7890qrst",
    "size": 100
  },
  "layers": [
    {
      "mediaType": "application/vnd.ironcore.image.disk.img",
      "digest": "sha256:diskimgdigestabcd1234efgh5678ijkl9012mnop3456qrst7890",
      "size": 1073741824
    },
    {
      "mediaType": "application/vnd.ironcore.image.kernel",
      "digest": "sha256:kernelabcd1234efgh5678ijkl9012mnop3456qrst7890uvwx1234",
      "size": 10485760
    },
    {
      "mediaType": "application/vnd.ironcore.image.initramfs",
      "digest": "sha256:initramfsabcd1234efgh5678ijkl9012mnop3456qrst7890uvwx1234",
      "size": 20971520
    },
    {
      "mediaType": "application/vnd.ironcore.image.squashfs",
      "digest": "sha256:squashfsabcd1234efgh5678ijkl9012mnop3456qrst7890uvwx1234",
      "size": 536870912
    },
    {
      "mediaType": "application/vnd.ironcore.image.cmdline",
      "digest": "sha256:cmdlineabcd1234efgh5678ijkl9012mnop3456qrst7890uvwx1234",
      "size": 1024
    },
    {
      "mediaType": "application/vnd.ironcore.image.uki",
      "digest": "sha256:ukiabcd1234efgh5678ijkl9012mnop3456qrst7890uvwx1234",
      "size": 15728640
    },
    {
      "mediaType": "application/vnd.ironcore.image.iso",
      "digest": "sha256:isoabcd1234efgh5678ijkl9012mnop3456qrst7890uvwx1234",
      "size": 734003200
    }
  ],
  "annotations": {
    "org.opencontainers.image.title": "MyOS Virtualization (amd64)",
    "variant": "virtualization",
    "architecture": "amd64"
  }
}

The manifest above describes the core components of an IronCore OCI image including the root disk image, kernel, initramfs, etc. The annotations field provides metadata about the image, such as its title, variant, and architecture.

Multiple Architectures Images

IronCore supports multi-architecture images, allowing you to build and publish images for different CPU architectures. This is done by providing an index manifest that references multiple architecture-specific manifests.

Below is an example of an index manifest for a multi-architecture image:

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.index.v1+json",
  "manifests": [
    {
      "mediaType": "application/vnd.ironcore.image.artifacts.v1+json",
      "digest": "sha256:ijkl9012qrst7890uvwx1234yzab5678abcd1234efgh5678mnop3456",
      "size": 2345,
      "platform": {
        "architecture": "amd64",
        "os": "linux"
      }
    },
    {
      "mediaType": "application/vnd.ironcore.image.artifacts.v1+json",
      "digest": "sha256:mnop3456qrst7890uvwx1234yzab5678abcd1234efgh5678ijkl9012",
      "size": 6789,
      "platform": {
        "architecture": "arm64",
        "os": "linux"
      }
    }
  ]
}

This index manifest references two architecture-specific manifests, one for amd64 and one for arm64. Each manifest contains a reference to the actual image layers and configuration for that specific architecture.