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