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Update readme for containerd

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Michael Crosby 2016-11-28 15:15:21 -08:00
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# containerkit # containerd
containerkit is a collection of components for building a fully featured container runtime, storage, and distribution layers in high level projects. containerd is a daemon for managing images and containers on a single host.
It is built to be multi-tenant and handle multiple clients for container runtime needs.
## Features
* OCI Image Spec support
* OCI Runtime Spec support
* Image push and pull support
* Container runtime and lifecycle support
* Network primitives for creation, modification, and deletion of interfaces
* Multi-tenant supported with CAS storage for global images
## Scope and Principles ## Scope and Principles
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### Components ### Components
containerkit is a collection of components. Components should not have tight dependencies on each other so that they are unable to be used independently.
These components can be used independently or together. The APIs for images and containers should be designed in a way that when used together the components have a natural flow but still be useful independently.
They should not have tight dependencies on each other so that they are unable to be used independently but should be designed in a way that when used together the components have a natural flow to the APIs.
An example for this design can be seen with the overlay filesystems and the container execution layer. An example for this design can be seen with the overlay filesystems and the container execution layer.
The execution layer and overlay filesystems can be used independently but if you were to use both, they share a common `Mount` struct that the filesystems produce and the execution layer consumes to start a container inside a root filesystem. The execution layer and overlay filesystems can be used independently but if you were to use both, they share a common `Mount` struct that the filesystems produce and the execution layer consumes.
### Primitives ### Primitives
containerkit should expose primitives to solve problems instead of building high level abstractions. containerd should expose primitives to solve problems instead of building high level abstractions in the API.
A common example of this is how build is implemented. A common example of this is how build would be implemented.
Instead of having a build API in containerkit we should expose the lower level primitives that allow things like build to work. Instead of having a build API in containerd we should expose the lower level primitives that allow things required in build to work.
Breaking up the filesystem APIs to allow snapshots, copy functionality, and mounts allow people implementing build at the higher levels more flexibility. Breaking up the filesystem APIs to allow snapshots, copy functionality, and mounts allow people implementing build at the higher levels more flexibility.
### Extensibility and Defaults ### Extensibility and Defaults
For the various components in containerkit there should be defined extension points where implementations can be swapped for alternatives. For the various components in containerd there should be defined extension points where implementations can be swapped for alternatives.
The best example of this is that containerkit will use `runc` from OCI as the default runtime in the execution layer but for other runtimes conforming to the OCI Runtime specification they can be easily added to contianerkit. The best example of this is that containerd will use `runc` from OCI as the default runtime in the execution layer but other runtimes conforming to the OCI Runtime specification they can be easily added to containerd.
containerkit will come with a default implementation for the various components. containerd will come with a default implementation for the various components.
These defaults will be chosen my the maintainers of the project and should not change unless better tech for that component comes out. These defaults will be chosen my the maintainers of the project and should not change unless better tech for that component comes out.
Additional implementations will not be accepted into the core repository and should be developed in a separate repository not maintained by the containerkit maintainers. Additional implementations will not be accepted into the core repository and should be developed in a separate repository not maintained by the containerd maintainers.
### Stability ### Releases
Containerd will be released with a 1.0 when feature complete and this version will be supported for 1 year with security and bug fixes applied and released.
The upgrade path for containerd is that the 0.0.x patch relases are always backward compatible with its major and minor version.
Minor (0.x.0) version will always be compatible with the previous minor release. i.e. 1.2.0 is backwards compatible with 1.1.0 and 1.1.0 is compatible with 1.0.0.
There is no compatiability guarentes with upgrades from two minor relases. i.e. 1.0.0 to 1.2.0.
There are not backwards compatability guarentes with upgrades to major versions. i.e 1.0.0 to 2.0.0.
Each major version will be supported for 1 year with bug fixes and security patches.
### Scope ### Scope
The following table specifies the various components of containerkit and general features of container runtimes. The following table specifies the various components of containerd and general features of container runtimes.
The table specifies whether or not the feature/component is in or out of scope. The table specifies whether or not the feature/component is in or out of scope.
| Name | Description | In/Out | Reason | | Name | Description | In/Out | Reason |
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| cow filesystem | Built in functionality for overlay, aufs, and other copy on write filesystems for containers | in | | | cow filesystem | Built in functionality for overlay, aufs, and other copy on write filesystems for containers | in | |
| distribution | Having the ability to push, pull, package, and sign images | in | | | distribution | Having the ability to push, pull, package, and sign images | in | |
| networking | Providing network functionality to containers along with configuring their network namespaces | in | | | networking | Providing network functionality to containers along with configuring their network namespaces | in | |
| build | Building images as a first class API | out | Build is a higher level tooling feature and can be implemented in many different ways on top of containerkit | | build | Building images as a first class API | out | Build is a higher level tooling feature and can be implemented in many different ways on top of containerd |
| volumes | Provide primitives for volumes and persistent storage | | | | volumes | Provide primitives for volumes and persistent storage | | |
containerkit is scoped to a single host. containerd is scoped to a single host.
It can be used to builds things like a node agent that launches containers but does not have any concepts of a distributed system. It can be used to builds things like a node agent that launches containers but does not have any concepts of a distributed system.
Also things like service discovery are out of scope even though networking is in scope. Also things like service discovery are out of scope even though networking is in scope.
containerkit should provide the primitives to create, add, remove, or manage network interfaces for a container but ip allocation, discovery, and DNS should be handled at higher layers. containerd should provide the primitives to create, add, remove, or manage network interfaces for a container but ip allocation, discovery, and DNS should be handled at higher layers.
### How is the scope changed? ### How is the scope changed?