45 lines
2.5 KiB
Markdown
45 lines
2.5 KiB
Markdown
`storage` is a Go library which aims to provide methods for storing filesystem
|
|
layers, container images, and containers. An `oci-storage` CLI wrapper is also
|
|
included for manual and scripting use.
|
|
|
|
To build the CLI wrapper, use 'make build-binary', optionally passing
|
|
'AUTO_GOPATH=1' as an additional argument to avoid having to set $GOPATH
|
|
manually. For information on other recognized targets, run 'make help'.
|
|
|
|
Operations which use VMs expect to launch them using 'vagrant', defaulting to
|
|
using its 'libvirt' provider. The boxes used are also available for the
|
|
'virtualbox' provider, and can be selected by setting $VAGRANT_PROVIDER to
|
|
'virtualbox' before kicking off the build.
|
|
|
|
The library manages three types of items: layers, images, and containers.
|
|
|
|
A *layer* is a copy-on-write filesystem which is notionally stored as a set of
|
|
changes relative to its *parent* layer, if it has one. A given layer can only
|
|
have one parent, but any layer can be the parent of multiple layers. Layers
|
|
which are parents of other layers should be treated as read-only.
|
|
|
|
An *image* is a reference to a particular layer (its _top_ layer), along with
|
|
other information which the library can manage for the convenience of its
|
|
caller. This information typically includes configuration templates for
|
|
running a binary contained within the image's layers, and may include
|
|
cryptographic signatures. Multiple images can reference the same layer, as the
|
|
differences between two images may not be in their layer contents.
|
|
|
|
A *container* is a read-write layer which is a child of an image's top layer,
|
|
along with information which the library can manage for the convenience of its
|
|
caller. This information typically includes configuration information for
|
|
running the specific container. Multiple containers can be derived from a
|
|
single image.
|
|
|
|
Layers, images, and containers are represented primarily by 32 character
|
|
hexadecimal IDs, but items of each kind can also have one or more arbitrary
|
|
names attached to them, which the library will automatically resolve to IDs
|
|
when they are passed in to API calls which expect IDs.
|
|
|
|
The library can store what it calls *metadata* for each of these types of
|
|
items. This is expected to be a small piece of data, since it is cached in
|
|
memory and stored along with the library's own bookkeeping information.
|
|
|
|
Additionally, the library can store one or more of what it calls *big data* for
|
|
images and containers. This is a named chunk of larger data, which is only in
|
|
memory when it is being read from or being written to its own disk file.
|