Dobby Overview

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.

Dobby is designed to be used for starting, stopping and monitoring all containerised applications on an RDK-V device. To start a container with Dobby, provide Dobby with a path to an OCI bundle and a container ID, and Dobby will handle the rest.

Written in C++ and with a plugin-based architecture, Dobby is lightweight, highly expandable and customisable, offering the ability to run custom code at various stages in the container lifecycle to add additional functionality. Out of the box, Dobby provides a number of plugins ready for use to provide commonly needed functionality including:

• Advanced container networking support with NAT and both IPv4 and IPv6 support. Allows for easily adding iptables rules to allow/prevent traffic flow in and out of container
• GPU memory limiting (providing the kernel has the appropriate support)
• Container log management to either files or directly to journald
• Loopback storage mounts to add persistent, isolated storage to containers
• IPC support between containers/host by allowing access to the host dbus inside containers

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.

Usage

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 dobby.service, which allows Dobby to be started/stopped by systemd.

Command-Line

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.

Integration with Thunder

OCIContainers Plugin

To control Dobby using a JSON-RPC API, then use the OCIContainer Thunder NanoService. This 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:

$ 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-]"
   }
}'

{
   "jsonrpc":"2.0",
   "id":3,
   "result":{
      "descriptor":257,
      "success":true
   }
}

The OCIContainer code  contains a README.md file with detailed documentation on its usage -  see here: https://github.com/rdkcentral/rdkservices/blob/sprint/2009/OCIContainer/README.md

ProcessContainers

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:

• -DPROCESS_CONTAINERS=ON
• -DPROCESSCONTAINERS_DOBBY=ON

Then for the plugin(s) you wish to run in a container, set the execution mode to "container" in the plugin configuration file.

Creating OCI bundles for Dobby

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:

• Root file system - a directory containing the root filesystem of the container
• Config.json - the container configuration

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 specification.

For more information on how to create OCI bundles from scratch, see the following pages:

• https://github.com/opencontainers/runtime-spec/blob/master/bundle.md
• https://github.com/opencontainers/runc#creating-an-oci-bundle
• https://chromium.googlesource.com/external/github.com/docker/containerd/+/refs/tags/v0.2.0/docs/bundle.md

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