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Table of Contents

Key Info

BundleGen is a command-line tool to convert OCI Images into extended OCI Bundles for use with the Dobby container manager. 

Background - Container Images vs Bundles

In OCI, there are two distinct ways of packing applications for containers - Images and Bundles.

Images

At a high-level an OCI implementation would download an OCI Image then convert that image into an OCI Runtime filesystem bundle. At this point the OCI Runtime Bundle would be run by an OCI Runtime.

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Once built, an OCI Image can then be uploaded to a registry server and discovered by name, downloaded, verified by hash, trusted through a signature, and converted into the runtime bundle ready to run by the runtime.

Bundles

Once the image is unpacked and converted into a bundle, this bundle can be used to launch a container using an OCI compliant runtime. The bundle consists of two parts:

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The bundle contains an OCI configuration file (which is named config.json) which can specify host-independent details such as which executable to launch and host-specific settings such as mount locations, hook paths, Linux namespaces and cgroups. Because the configuration includes host-specific settings, application bundle directories copied between two hosts may require configuration adjustments.

Creating OCI Bundles Manually

It is possible to manually create an OCI bundle from scratch by hand-crafting the runtime configuration and copying files into the rootfs. For more information on how to create OCI bundles from scratch, see the following pages:

The Need for BundleGen

As part of the DAC project, Consult Red created a standalone tool to accompany Dobby called BundleGen.

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  1. Obtain the OCI Image using Skopeo (open-source tool by RedHat)

  2. Unpack the OCI image with Umoci (open-source tool by OCI)

  3. Validate App is compatible

  4. Modify the OCI config based on the platform template. This includes but is not limited to:

    1. Environment Variables

    2. Mounts for sockets, libraries

    3. Device whitelisting

    4. User and groups

    5. RDK plugins (networking, loopback mounts, logging)

  5. Create .tar.gz from bundle with modified config

App Metadata

To create a bundle that is compatible for an application, BundleGen requires a small amount of metadata about the application. This can be thought of as similar to a manifest in Android apps. The app metadata can include information about storage and memory requirements, whether the app needs graphics support and network access such as port forwarding.

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The example images built by the SDK contain metadata files which are the embedded inside the OCI image for BundleGen to use: https://github.com/stagingrdkm/meta-dac-sdk/tree/master/recipes-example/images/metadatas

Non SDK Generated Images

If using images from the Docker hub or other OCI registry that were not generated by the DAC SDK, then you will need to manually write a metadata file for the app and provide the file to BundleGen in the generate command via the optional --appmetadata argument.

Usage

Before you can use BundleGen, you must create an OCI image containing your application using the SDK and upload it to an OCI registry such as the Docker Hub. Once that is complete, follow the below instructions to use BundleGen.

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