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Draft page for review and comment prior to publication. |
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Downloadable Application Containers (DAC) is a pan-RDK initiative to develop a container solution that allows binary applications to be downloaded and run on STBs without modification. DAC is initially targeting RDK-V set-top boxes but the aim is to extend DAC to suitable RDK-B devices in due course. DAC is a co-operation effort between Comcast, Sky, Liberty Global, Metrological and Consult Red.
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Crun is a different implementation of an OCI runtime, this time written in C and optimised for performance and a low memory footprint. It is developed at RedHat and is currently in use by Podman in Fedora, and is planned to be used in a main RHEL release soon. This is the runtime supported by Dobby and will be used in as the default runtime across RDK.
Dobby is a container management tool, originally developed by Sky and open-sourced to the RDK community. Dobby is a daemon-based program that makes use of the crun runtime and provides a more user-friendly experience for starting/stopping containers, handles container lifecycle management and enhancing the base functionality provided by crun.
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Plugins are C++ code written against the plugin interface, allowing for operators to easily add additional functionality, or modify existing functionality easily. All the plugins for Dobby can be found in the RDKPlugins directory in the repo here: https://github.com/rdkcentral/Dobby/tree/master/rdkPlugins. Each plugin contains a README file with documentation on its usage. The TestPlugin is designed as a minimal reference plugin that can be used as an example for your own development. Note there is a directory in the Dobby repo called plugins which containers legacy plugins required for some platforms. These should not be used as a reference for new plugins.
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The core component of Dobby is the DobbyDaemon. This should be started at STB boot and then listens over dbus for commands. The full dbus API of Dobby can be found here: https://github.com/rdkcentral/Dobby/blob/master/protocol/include/DobbyProtocol.h, although it is not recommended to communicate with Dobby manually over dbus. Instead, Dobby provides abstractions over dbus which are discussed later in this document.
Dobby ships with a systemd unit file called sky-dobby.service, which allows Dobby to be started/stopped by systemd. DobbyDaemon logs are sent to journald.Once the daemon is running, there are a number of ways to interact with Dobby
For debug builds of Dobby, the DobbyTool binary is installed on the STB. This is a simple command line app that communicates with Dobby directly over dbus to issue common commands. This is very useful for troubleshooting and testing Dobby.
DobbyTool offers the following commands:
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vagrant@dobby-vagrant:~/srcDobby/build$ DobbyTool help quit quit help help [command] shutdown shutdown start start [options...] <id> <specfile/bundlepath> [command] stop stop <id> [options...] pause pause <id> resume resume <id> exec exec [options...] <id> <command> list list info info <id> dumpspec dumpspec <id> [options...] bundle bundle <id> <specfile> [options...] set-dbus set-dbus <private>|<public> <address> |
Some commands offered by DobbyTool (mainly dumpspec) are to allow compatibility with the legacy Dobby Spec input format (instead of OCI bundles), which are deprecated and maintained only for backwards compatibility with existing deployments.
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To control Dobby using a JSON-RPC API, then use the OCIContainer Thunder NanoService. The source code for OCIContainer can be found here https://github.com/rdkcentral/rdkservices/tree/master/OCIContainerThis exposes the same functionality as DobbyTool, but in a manner more suited for integration into other code. Example of OCIContainer to start a container from an OCI bundle:
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$ curl -X POST http://127.0.0.1:9998/jsonrpc/ -d '{
"jsonrpc":"2.0",
"id":3,
"method":"org.rdk.OCIContainer.1.startContainer",
"params":{
"containerId": "testContainer",
"bundlePath": "[-INSERT BUNDLE PATH-]"
}
}' |
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{
"jsonrpc":"2.0",
"id":3,
"result":{
"descriptor":257,
"success":true
}
} |
The OCIContainer code OCIContainer code contains a README.md file with detailed documentation on its usage , and includes a test script (test/ociContainerTest.sh) that can be used to ensure Dobby/OCIContainer is working as expected- see here: https://github.com/rdkcentral/rdkservices/blob/sprint/2009/OCIContainer/README.md
Thunder includes the ability to run plugins in containers as well as the traditional in/out of process modes. Thunder offers different back-ends for running Thunder plugins in containers, one of which is Dobby. This mode will communicate with Dobby to start/stop Thunder plugins inside Dobby containers. This provides the advantage of meaning Dobby is responsible for running all types of container on the STB, from native apps to Thunder plugins.
To enable this, compile Thunder with the following CMake flags:
Then for the plugin(s) you wish to run in a container, set the execution mode to "container" in the plugin configuration file.
To run an application as a Dobby container, the application must be packed as an OCI bundle. This bundle can come from many different sources - it could be manually created or generated from an OCI image.
An OCI bundle consists of two key components:
The exact structure of this bundle is defined in the OCI runtime specification here: https://github.com/opencontainers/runtime-spec/blob/master/spec.md. Dobby is fully compliant with version 1.0.2 of the specificationThe Dobby source code contains a few example OCI bundles in the tests directory, although more tooling to allow easier generation of OCI bundles is under development.
For more information on how to create OCI bundles from scratch, see the following pages:
As part of the DAC project, Consult Red created a standalone tool to accompany Dobby called BundleGen. This is a command line tool designed to convert OCI images into OCI bundles that can be run by Dobby. BundleGen is designed to run off-box in a cloud environment and uses template files to create the bundles tailed for a given RDK platform. The repo includes sample templates for the Dobby Vagrant VM and the RPi.
For more information and documentation on BundleGen, see the repo here: https://github.com/rdkcentral/BundleGen/tree/master/docs
Dobby source code lives on the RDKCentral GitHub here: https://github.com/rdkcentral/Dobby and is Apache 2.0 licenced.
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