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Draft page for review and comment prior to publication.
Individual components are explained in more detail in the relevant sub-pages. Proposed organisation:
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.
DAC builds upon open-source specifications, components and tools from the Open Container Initiative (OCI). In particular, it uses crun, a fast, small, OCI-runtime compliant engine that can configure and launch applications containers. As part of the DAC project, a number of new open-source components have been contributed to RDK including:
These are the first components of an end-to-end system that operators can use to adapt, manage and control containers to be suitable for their platform.
Other components within the end-to-end system that are currently in development include RDK-V SDK extensions that allow DAC Apps to be: built, published, and then adapted before loading and running on RDK-V STBs. The work for this is co-ordinated by RDK DAC Special interest Group (RDKDACSIG)
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.
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:
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/):
The Open Container Initiative is an open governance structure for the express purpose of creating open industry standards around container formats and runtimes.
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.
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: