This section defines a format for encoding a container as a bundle - a directory organized in a certain way, and containing all the necessary data and metadata for any compliant runtime to perform all standard operations against it. See also OS X application bundles for a similar use of the term bundle.
The format does not define distribution. In other words, it only specifies how a container must be stored on a local filesystem, for consumption by a runtime. It does not specify how to transfer a container between computers, how to discover containers, or assign names or versions to them. Any distribution method capable of preserving the original layout of a container, as specified here, is considered compliant.
A standard container bundle is made of the following 3 parts:
- A top-level directory holding everything else
- One or more content directories
- A configuration file
A Standard Container bundle is a directory containing all the content needed to load and run a container.
This includes two configuration files config.json and runtime.json, and a rootfs directory.
The config.json file contains settings that are host independent and application specific such as security permissions, environment variables and arguments.
The runtime.json file contains settings that are host specific such as memory limits, local device access and mount points.
The goal is that the bundle can be moved as a unit to another machine and run the same application if runtime.json is removed or reconfigured.
Configuration file syntax and semantics:
config.json(immutable, host independent configuration)runtime.json(mutable, host dependent configuration)
A single rootfs directory MUST be in the same directory as the config.json.
The names of the directories may be arbitrary, but users should consider using conventional names as in the example below.
config.json
runtime.json
rootfs/