forked from TrueCloudLab/distribution
Refactor Blob Service API
This PR refactors the blob service API to be oriented around blob descriptors. Identified by digests, blobs become an abstract entity that can be read and written using a descriptor as a handle. This allows blobs to take many forms, such as a ReadSeekCloser or a simple byte buffer, allowing blob oriented operations to better integrate with blob agnostic APIs (such as the `io` package). The error definitions are now better organized to reflect conditions that can only be seen when interacting with the blob API. The main benefit of this is to separate the much smaller metadata from large file storage. Many benefits also follow from this. Reading and writing has been separated into discrete services. Backend implementation is also simplified, by reducing the amount of metadata that needs to be picked up to simply serve a read. This also improves cacheability. "Opening" a blob simply consists of an access check (Stat) and a path calculation. Caching is greatly simplified and we've made the mapping of provisional to canonical hashes a first-class concept. BlobDescriptorService and BlobProvider can be combined in different ways to achieve varying effects. Recommend Review Approach ------------------------- This is a very large patch. While apologies are in order, we are getting a considerable amount of refactoring. Most changes follow from the changes to the root package (distribution), so start there. From there, the main changes are in storage. Looking at (*repository).Blobs will help to understand the how the linkedBlobStore is wired. One can explore the internals within and also branch out into understanding the changes to the caching layer. Following the descriptions below will also help to guide you. To reduce the chances for regressions, it was critical that major changes to unit tests were avoided. Where possible, they are left untouched and where not, the spirit is hopefully captured. Pay particular attention to where behavior may have changed. Storage ------- The primary changes to the `storage` package, other than the interface updates, were to merge the layerstore and blobstore. Blob access is now layered even further. The first layer, blobStore, exposes a global `BlobStatter` and `BlobProvider`. Operations here provide a fast path for most read operations that don't take access control into account. The `linkedBlobStore` layers on top of the `blobStore`, providing repository- scoped blob link management in the backend. The `linkedBlobStore` implements the full `BlobStore` suite, providing access-controlled, repository-local blob writers. The abstraction between the two is slightly broken in that `linkedBlobStore` is the only channel under which one can write into the global blob store. The `linkedBlobStore` also provides flexibility in that it can act over different link sets depending on configuration. This allows us to use the same code for signature links, manifest links and blob links. Eventually, we will fully consolidate this storage. The improved cache flow comes from the `linkedBlobStatter` component of `linkedBlobStore`. Using a `cachedBlobStatter`, these combine together to provide a simple cache hierarchy that should streamline access checks on read and write operations, or at least provide a single path to optimize. The metrics have been changed in a slightly incompatible way since the former operations, Fetch and Exists, are no longer relevant. The fileWriter and fileReader have been slightly modified to support the rest of the changes. The most interesting is the removal of the `Stat` call from `newFileReader`. This was the source of unnecessary round trips that were only present to look up the size of the resulting reader. Now, one must simply pass in the size, requiring the caller to decide whether or not the `Stat` call is appropriate. In several cases, it turned out the caller already had the size already. The `WriterAt` implementation has been removed from `fileWriter`, since it is no longer required for `BlobWriter`, reducing the number of paths which writes may take. Cache ----- Unfortunately, the `cache` package required a near full rewrite. It was pretty mechanical in that the cache is oriented around the `BlobDescriptorService` slightly modified to include the ability to set the values for individual digests. While the implementation is oriented towards caching, it can act as a primary store. Provisions are in place to have repository local metadata, in addition to global metadata. Fallback is implemented as a part of the storage package to maintain this flexibility. One unfortunate side-effect is that caching is now repository-scoped, rather than global. This should have little effect on performance but may increase memory usage. Handlers -------- The `handlers` package has been updated to leverage the new API. For the most part, the changes are superficial or mechanical based on the API changes. This did expose a bug in the handling of provisional vs canonical digests that was fixed in the unit tests. Configuration ------------- One user-facing change has been made to the configuration and is updated in the associated documentation. The `layerinfo` cache parameter has been deprecated by the `blobdescriptor` cache parameter. Both are equivalent and configuration files should be backward compatible. Notifications ------------- Changes the `notification` package are simply to support the interface changes. Context ------- A small change has been made to the tracing log-level. Traces have been moved from "info" to "debug" level to reduce output when not needed. Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day
parent
dc348d720b
commit
08401cfdd6
44 changed files with 2426 additions and 2270 deletions
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@ -30,7 +30,7 @@ const storagePathVersion = "v2"
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// -> <algorithm>/<hex digest>/link
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// -> _layers/
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// <layer links to blob store>
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// -> _uploads/<uuid>
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// -> _uploads/<id>
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// data
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// startedat
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// hashstates/<algorithm>/<offset>
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@ -47,7 +47,7 @@ const storagePathVersion = "v2"
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// is just a directory of layers which are "linked" into a repository. A layer
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// can only be accessed through a qualified repository name if it is linked in
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// the repository. Uploads of layers are managed in the uploads directory,
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// which is key by upload uuid. When all data for an upload is received, the
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// which is key by upload id. When all data for an upload is received, the
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// data is moved into the blob store and the upload directory is deleted.
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// Abandoned uploads can be garbage collected by reading the startedat file
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// and removing uploads that have been active for longer than a certain time.
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@ -80,20 +80,21 @@ const storagePathVersion = "v2"
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// manifestTagIndexEntryPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/index/<algorithm>/<hex digest>/
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// manifestTagIndexEntryLinkPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/index/<algorithm>/<hex digest>/link
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//
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// Layers:
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// Blobs:
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//
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// layerLinkPathSpec: <root>/v2/repositories/<name>/_layers/tarsum/<tarsum version>/<tarsum hash alg>/<tarsum hash>/link
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// layerLinkPathSpec: <root>/v2/repositories/<name>/_layers/<algorithm>/<hex digest>/link
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//
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// Uploads:
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//
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// uploadDataPathSpec: <root>/v2/repositories/<name>/_uploads/<uuid>/data
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// uploadStartedAtPathSpec: <root>/v2/repositories/<name>/_uploads/<uuid>/startedat
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// uploadHashStatePathSpec: <root>/v2/repositories/<name>/_uploads/<uuid>/hashstates/<algorithm>/<offset>
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// uploadDataPathSpec: <root>/v2/repositories/<name>/_uploads/<id>/data
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// uploadStartedAtPathSpec: <root>/v2/repositories/<name>/_uploads/<id>/startedat
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// uploadHashStatePathSpec: <root>/v2/repositories/<name>/_uploads/<id>/hashstates/<algorithm>/<offset>
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//
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// Blob Store:
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//
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// blobPathSpec: <root>/v2/blobs/<algorithm>/<first two hex bytes of digest>/<hex digest>
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// blobDataPathSpec: <root>/v2/blobs/<algorithm>/<first two hex bytes of digest>/<hex digest>/data
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// blobMediaTypePathSpec: <root>/v2/blobs/<algorithm>/<first two hex bytes of digest>/<hex digest>/data
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//
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// For more information on the semantic meaning of each path and their
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// contents, please see the path spec documentation.
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@ -234,9 +235,14 @@ func (pm *pathMapper) path(spec pathSpec) (string, error) {
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return "", err
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}
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layerLinkPathComponents := append(repoPrefix, v.name, "_layers")
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// TODO(stevvooe): Right now, all blobs are linked under "_layers". If
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// we have future migrations, we may want to rename this to "_blobs".
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// A migration strategy would simply leave existing items in place and
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// write the new paths, commit a file then delete the old files.
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return path.Join(path.Join(append(layerLinkPathComponents, components...)...), "link"), nil
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blobLinkPathComponents := append(repoPrefix, v.name, "_layers")
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return path.Join(path.Join(append(blobLinkPathComponents, components...)...), "link"), nil
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case blobDataPathSpec:
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components, err := digestPathComponents(v.digest, true)
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if err != nil {
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@ -248,15 +254,15 @@ func (pm *pathMapper) path(spec pathSpec) (string, error) {
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return path.Join(append(blobPathPrefix, components...)...), nil
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case uploadDataPathSpec:
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return path.Join(append(repoPrefix, v.name, "_uploads", v.uuid, "data")...), nil
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return path.Join(append(repoPrefix, v.name, "_uploads", v.id, "data")...), nil
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case uploadStartedAtPathSpec:
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return path.Join(append(repoPrefix, v.name, "_uploads", v.uuid, "startedat")...), nil
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return path.Join(append(repoPrefix, v.name, "_uploads", v.id, "startedat")...), nil
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case uploadHashStatePathSpec:
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offset := fmt.Sprintf("%d", v.offset)
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if v.list {
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offset = "" // Limit to the prefix for listing offsets.
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}
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return path.Join(append(repoPrefix, v.name, "_uploads", v.uuid, "hashstates", v.alg, offset)...), nil
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return path.Join(append(repoPrefix, v.name, "_uploads", v.id, "hashstates", v.alg, offset)...), nil
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case repositoriesRootPathSpec:
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return path.Join(repoPrefix...), nil
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default:
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@ -367,8 +373,8 @@ type manifestTagIndexEntryLinkPathSpec struct {
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func (manifestTagIndexEntryLinkPathSpec) pathSpec() {}
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// layerLink specifies a path for a layer link, which is a file with a blob
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// id. The layer link will contain a content addressable blob id reference
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// blobLinkPathSpec specifies a path for a blob link, which is a file with a
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// blob id. The blob link will contain a content addressable blob id reference
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// into the blob store. The format of the contents is as follows:
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//
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// <algorithm>:<hex digest of layer data>
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@ -377,7 +383,7 @@ func (manifestTagIndexEntryLinkPathSpec) pathSpec() {}
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//
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// sha256:96443a84ce518ac22acb2e985eda402b58ac19ce6f91980bde63726a79d80b36
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//
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// This says indicates that there is a blob with the id/digest, calculated via
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// This indicates that there is a blob with the id/digest, calculated via
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// sha256 that can be fetched from the blob store.
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type layerLinkPathSpec struct {
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name string
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@ -415,7 +421,7 @@ func (blobDataPathSpec) pathSpec() {}
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// uploads.
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type uploadDataPathSpec struct {
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name string
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uuid string
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id string
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}
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func (uploadDataPathSpec) pathSpec() {}
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@ -429,7 +435,7 @@ func (uploadDataPathSpec) pathSpec() {}
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// the client to enforce time out policies.
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type uploadStartedAtPathSpec struct {
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name string
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uuid string
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id string
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}
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func (uploadStartedAtPathSpec) pathSpec() {}
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@ -437,10 +443,10 @@ func (uploadStartedAtPathSpec) pathSpec() {}
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// uploadHashStatePathSpec defines the path parameters for the file that stores
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// the hash function state of an upload at a specific byte offset. If `list` is
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// set, then the path mapper will generate a list prefix for all hash state
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// offsets for the upload identified by the name, uuid, and alg.
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// offsets for the upload identified by the name, id, and alg.
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type uploadHashStatePathSpec struct {
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name string
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uuid string
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id string
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alg string
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offset int64
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list bool
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