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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. The work for this is co-ordinated by RDK DAC Special interest Group (RDKDACSIG)
an RDK initiative and cooperation effort between Comcast, Sky, Liberty Global, RDK-M and Consult Red. The work for this is co-ordinated by RDK DAC Special Interest Group (RDKDACSIG)
The DAC end goal is to provide a solution that allows app developers to write and package also native (c/c++) Applications in a way that makes the application binary exchangeable and can be run across all RDK boxes without (compile time) modifications.
This group initially focused on RDK-V, the solution described on this wiki page is focused on RDK-V but many of the principles/same components are also suitable for RDK-B.
The diagram above provides a high level overview of the DAC solution.
It is divided into 4 functional areas which we describe futher in sections below:
This video, made by ConsultRed at TechSummit2024, nicely explains this bigger picture: dac_overview_rdk_tech_summit_2024_1080p.mp4
Multimedia name dac_overview_rdk_tech_summit_2024_1080p.mp4
Below is a more detailed diagram with technical components inside the RDK6.1 SW on STB and DAC reference cloud
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3 functional area's are further discussed in sections below
The diagram above provides a high level end-2-end overview of system. It is divided into 3 functional areas:
These are discussed further in the following sections
A DAC SDK is created to make it easier for app developers to build oci, dac compliant containerized applications. The SDK is public, fully open source and uses standard Yocto 3.1 Dunfel Poky cross-compilation / build environment. It does NOT require you as an App developer to have any SoC or OEM specific SW/SDK for being able to compile and package your AppContainer, it is SOC/OEM agnostic. The SDK allows developers to cross compile their application sources, automatically add appropriate dependent libraries in AppContainer and produce oci, dobby, dac compliant AppContainer image. This binary oci AppContainer image can then be uploaded to an OCI registry for sharing with possible consumers/distribution platforms. As App developer you can test and run your AppContainer on all RDK6.1 RDK-M Video Accelerators (when publishing the App to RDK-M VA DAC cloud instance)
The DAC APP SDK is available on https://github.com/rdkcentral/meta-dac-sdk and comes with many example AppContainers
For information on how to make DAC app and use DAC SDK we refer to HOWTO build App with DAC SDK, cloudpublish and run on VA#useDACSDKandbuildyourfirstnativeDACapp
OCI container registry: is a standard Cloud Native component that allows storage and exchange of AppContainers in the standardized oci image format. see oci "Image Format Specification" by Open Container Initiative.
To allow distribution of its application ( to allow it to be run on RDK STBs), the App developer must upload its AppContainer to an oci container registry.
The OCI registry is the binary App exchange point between App developer and consuming parties/operators for distribution of the App on their target platforms.
To run the oci compliant AppContainer on set of devices in production, an associated secure distribution solution/system must be in place.
This distribution solution is responsibility of the operator and not of the app developer.
It is typically also a distribution system / instance per operator/environment because:
RDK provides a reference distribution solution, see the "DAC cloud reference" as depicted in reference architecture diagram above. It consists out of several µservices. If you hover over the specific µservice on the diagram you can see the link to its associated open source code.
RDK and RDK-M do not mandate use of a particular distribution solution towards the RDK operators.
The operators are free to choose, make/buy their secure distribution solution. Some operator choose to build further on system they already had, some operators are using their instance of the DAC cloud reference.
As long as the operator distribution system can take in the oci, dac compliant AppContainer, securely distribute and convert it to its OCI bundle equivalent ready for use on the operator specific CPE devices that support the dac contract for binary compatibility, it should be fine. In future we may want to validate this as part of firebolt certification of those devices.
RDK-M does operate an instance of the reference DAC cloud that serves an AppCatalog with DAC Appcontainers for all the RDK-M Video Accelerators
It is important staging, test and reference environment for App developers and RDK community, allowing App developers to publish their DAC native apps and test/run them on all the RDK Video Accelerators with a RDK6.1 software image (from 3 different SoC vendors).
Without such environment App developers cannot test and run their Application on real devices and that is obviously not acceptable.
If RDK-M organizes certification testing of a native Application, it will tested/certify against this environment
Operators will want to see the application successfully running and passing testing on this DAC Video accelerator environment before starting testing of the same app on their environment and boxes.
To be able to install and run the AppContainer on set of target devices/population following things are required:
The reference DAC cloud solution has been designed to fulfill those requirements.
In the architecture diagram you can find the bundle generator µservice that will upon RabbitMQ trigger automatically generate from an OCI image the appropriate OCI bundle for specific HWmodel (VA) and store it for downstream usage. It will use the appropriate config template for that associated HWmodel (see example HWmodel specific templates here ) for generation of the run config.json. The bundlegen code that the µservice is executing during this bundlegeneration of an app is located here.
In the architecture diagram you can find the bundle cryptor µservice that will upon generation of new bundle by bundlegeneration service, sign and encrypt the bundle. For more information on that we refer to DAC session at Technology Summit 2023#pane-uid-b13cbeba-87dc-4f0a-9932-5b7e00770663-1 and documentation on access restricted page DAC Security
That is what the reference DAC cloud system is doing. Once bundle for particular app_id/platform/compatible version is created, it will be available in cache of ASCS (Appstore Caching service) (which can serve as the origin for further caching on a CDN). If you request bundle for particular app_id/platform/compatibleversion towards ASCS and if it is not available in its cache it will automatically trigger real time creation of associated bundle in a flow managed by ASBS (appstore bundle service). ASBS will fetch appropriate metadata from ASMS and give instructions with right input parameters to respectively bundle-generator-service and bundle-cryptor-service via RabbitMQ to generate and secure the bundle and cache on ASCS.
The core components in any RDK software image to run the Appscontainer on CPE are "Dobby" and "crun". Dobby is an OCI Container manager aka container engine comparable to known desktop container engines dockerd and podman but then focused on embedded device, written in C++ and designed to have minimal footprint and performance impact.
Crun is an opensource container runtime alternative to "runc" equivalent but written in C, has smaller footprint but is also well supported by the industry (is for example default container runtime used by podman)
Dobby exposes API and DAC provides all the necessary tooling to run containerised applications using OCI containers on an RDK-V STB. The main component of this is Dobby, an embedded-focused OCI container manager. Dobby is used to start, stop and monitor containers running on a STB, using the crun runtime underneath to interface with the kernel and start the containers. Dobby is written in C++ and designed to have minimal footprint and performance impact.
When requested to start a new container, crun will process the associated container configuration (run config.json) and apply the associated container policies/settings.
The OCIContainer Thunder plugin allows for interfacing with Dobby using a JSON-RPC interface , and Dobby can also be used to run other Thunder plugins in containers using the Dobby ProcessContainer backend.For For more information on Dobby, see the detailed documentation here: Dobby Documentation
As part of DAC, the RDKShell plugin has been extended to allow starting DAC apps using Dobby, creating a display and attaching it to the containerised app as necessary. RDKShell also integrates with the Packager plugin to provide a full-featured solution for downloading, installing and lifecycle management of DAC apps. For more documentation on the RDKShell and Packager integration see RDKShell and Packager - Downloading, Installing and Launching DACs. See the Getting Started section below for an example of using these components together.
To support the STB components, backend/cloud infrastructure has been developed. These components allow operators to create application submission portals where developers can submit their applications and their corresponding metadata. These submitted applications can then be converted from an OCI image to an OCI bundle ready for use on an operator's specific hardware.
The AppStore Metadata Service (ASMS) component provides APIs for both a developer and an STB to use to upload application metadata and search for previously uploaded applications. More documentation on ASMS can be found here: App Store Metadata Service (ASMS) Documentation
The BundleGen tool is a command-line tool that runs in the cloud to prepare containers for use on specific platforms. It uses template files created by an operator to ensure that the container is configured appropriately for the specific hardware requirements of an operators STB. This includes but is not limited to graphics libraries, sockets, IPC and network configuration. More detailed documentation for BundleGen can be found here: BundleGen Documentation
To develop DAC applications, an SDK has been developed that allows developers to write Bitbake recipes that compile their code and produce an OCI image. This OCI image can then be uploaded to an OCI registry where it can be converted and downloaded to a STB ready to be run by Dobby. The SDK is based on Yocto 3.1 Dunfell and does not require any RDK specific layers - instead it uses the standard Poky distribution and can run on a developer's workstation, independent of any other build systems. This decreases the amount of time it takes for a developer to build and test their application, reducing development time.
Apps build using the DAC SDK are also designed to be cross-platform, since the OCI image will contain all the necessary dependencies. Providing the platform supports the necessary DAC libraries such as Wayland, the application will run on that platform with no manual modifications.
As part of the SDK, a number of example application recipes are included such as a Wayland EGL and Qt application.
following wiki Dobby and for crun see the crun code repo.
Before being able to run the Appcontainer successfully on RDK CPE, other pieces are needed as well.
Some pieces may be operator-specific such as the UI to discover, store and run the apps but also not all operators will be using RDKshell as Appmanager and some will use alternative component to LISA for installation of apps. Also some may have system to distribute, store the apps onto the device without UI/user involved.
Operator device software must meet DAC contract for binary compatibility. Following firebolt native abstraction interfaces need to be in place: Rialto for audio, video & DRM and libGLESv2.so.2, libEGL.so.1, libwayland-egl.so.1 and libessos.so for Graphics. Also a Firebolt Server json-rpc server (which is "ripple" in RDK 6.1 reference environment) that supports current and upcoming Firebolt api version must be in place and pass certification tests (currently version 1.0 but we are working on and aim at 2.0 eg Lifecycle2 is required for native apps)
The RDK Video Accelerators running their RDK6.1 software image are the reference environment for RDK. They use the components as shown in the reference architecture diagram (VideoAccelerator UI, RDKshell with RialtoServermanager support, LISA, OCIcontainer rdkservice, OMI, ripple, westeros, dobby, crun. The Video Accelerator Resident App includes basic UI for working with DACapps. That UI allows you to browse and install DAC apps from the Appcatalog offered by ASMS in the DAC cloud instance setup for VA's. For demo video and more information on how to use that UI see video1 and video2.
That VA UI uses LISA API to get list of all installed apps at boot and for installing/uninstalling specific app.
For installation of a specific App, UI will ask for a particular app_id/app_version/HWplatform/compatibleFWversion combination the bundl_url to ASMS in DAC cloud and pass this bundle_url to LISA along with the install request. That URL will be https url pointing towards ASCS in DAC cloud with path towards actual (signed/encrypted) bundle tarball there. LISA will do the HTTPS request for that bundle tarbal. In regular case that bundle tarbal will be available in cache of ASCS or CDN in front and hence when LISA does the HTTPS request for that bundle tarbal, ASCS will be returned immediately with HTTP 200 OK. In case that bundle is not available in the cache yet (is the case when the bundle for that combination was not already pre-generated or requested by 1 other stb of same model), the ASCS will trigger ASBS in DAC cloud to automatically on the fly create the bundle for that combination (near Just in Time, eg 1-5 seconds order) and populate in the ASCS for download by LISA. In such "not in cache" case ASBS will return 202 iso 200 to LISA to indicate the near Just in Time generation and few seconds of patience. LISA has built-in, tunable by config, retry mechanism in case of such 202 so that it will also download the bundle in case of such near Just in time generation.
When successfully downloading the tarball LISA will unpack it in the appropriate directory locations it created for it, also create a separate persistent storage location for that app and add the app_id / version to its local database.
For more information on LISA we refer to LISA wiki https://wiki.rdkcentral.com/display/ASP/LISA
When the user wants to run one of the installed apps, the VA UI requests RDKshell, as the Appmanager, to start this app of type dac.native with as input the path to the associated bundle as stored by LISA.
RDKshell will create westeros wayland server instance/display socket for the app, create RialtoServer instance for the app (when needed), when Firebolt app interact with Firebolt Server (ripple) to get session_id for this app (is like security token, app needs when later connecting to Firebolt Server) and further delegate startContainer(bundle_path, westerosSocket) to OCIContainer thunder plugin which will in case of signed/encrypted container trigger the OMI component to verify signature and decrypt config.jwt in the crypted bundle and decrypt, verify and mount the rootfs of the Appcontainer rootfs using dm-verity & dm-crypt so it is ready to be consumed. Then the startContainer request is further delegated to Dobby which uses crun to execute it.
They will setup the container according to the associated run config.json, including bind mounts from STB host rootfs to Appcontainer rootfs of appropriate wayland and rialto server socket, as well as bind mounts of SoC specific Gfx library deps tree (that provide libGLESv2.so.2 and libEGL.so.1 )
When the dac.native app is a firebolt App, the specific Firebolt connection URL with session_id as security token, will be passed through the chain of RDKshell, OCI Container, dobby/crun and be available as an environment variable inside the Container. The app can then learn its value and use it when setting up connection with Firebolt Server.
Referring to the documentation HOWTO build App with DAC SDK, cloudpublish and run on VA The SDK is currently in Alpha and is subject to change as development continues. See here SDK Documentation for more information
Used heavily in modern cloud software, containers are a standardised way to run the software in a self-contained, isolated and secure environment. Containers contain everything an application needs to run, including code, libraries and other dependencies. This means that there is no need to install specific libraries and dependencies on the host for each application. Unlike more traditional virtual machines, containers are lightweight and fast to create and destroy and don't have the overhead of virtualising an entire operating system. By sharing the OS kernel between containers, running applications inside containers adds very little performance or footprint overhead.
The most popular containerisation solution currently in use is Docker, although there are a number of other solutions such as LXC, Singularity and Podman. LXC containers have been available within RDK for a number of years, using a container generation tool at build time to define and create the container configurations but for use within monolithic STB software image, not for device agnostic building and downloading separately from monolithic image what DAC is achieving.
Image source: https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/
There are a number of advantages of using containers to run applications in RDK deployments, including:
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As part of the DAC initiative, containers are used to reduce the difficulty of developing native applications that can be run on many different RDK-V devices from different operators by creating an isolated environment for each application. This means the app becomes platform agnostic and can be run on devices the develop may not have physical access to.
From the Open Container Initiative (OCI) website (https://opencontainers.org/):
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Formed in 2015 by Docker and other companies in the container industry and now part of the Linux Foundation, OCI define a number of specifications that allow developers to define containers. These specifications are followed by almost all major containerisation platforms.
OCI define both a runtime specification and an image specification. The Runtime Specification outlines how to run a “filesystem bundle” that is unpacked on disk. The OCI image is used for packaging containers in a platform-agnostic way that can be easily distributed. At a high-level, an OCI implementation would download an OCI Image then unpack 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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An OCI runtime is a CLI tool that allows for spawning and running containers according to the OCI specification. There are two main OCI runtimes in production use:
Refer to the quickstart documentation here: Quickstart: Building, Installing and Running DAC apps for instructions on how to create, build and run DAC applications on the Raspberry Pi reference platform