forked from TrueCloudLab/distribution
The toolkit to pack, ship, store, and deliver container content
593bbccdb5
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> |
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| cmd | ||
| configuration | ||
| context | ||
| contrib | ||
| digest | ||
| docs | ||
| Godeps | ||
| health | ||
| manifest | ||
| notifications | ||
| project | ||
| registry | ||
| testutil | ||
| version | ||
| .drone.yml | ||
| .gitignore | ||
| .mailmap | ||
| AUTHORS | ||
| blobs.go | ||
| circle.yml | ||
| CONTRIBUTING.md | ||
| doc.go | ||
| Dockerfile | ||
| errors.go | ||
| LICENSE | ||
| MAINTAINERS | ||
| Makefile | ||
| README.md | ||
| registry.go | ||
| ROADMAP.md | ||
Distribution
The Docker toolset to pack, ship, store, and deliver content.
This repository's main product is the Docker Registry 2.0 implementation for storing and distributing Docker images. It supersedes the docker/docker- registry project with a new API design, focused around security and performance.
This repository contains the following components:
| Component | Description |
|---|---|
| registry | An implementation of the Docker Registry HTTP API V2 for use with docker 1.6+. |
| libraries | A rich set of libraries for interacting with,distribution components. Please see godoc for details. Note: These libraries are unstable. |
| dist | An experimental tool to provide distribution, oriented functionality without the docker daemon. |
| specifications | Distribution related specifications are available in docs/spec |
| documentation | Docker's full documentation set is available at docs.docker.com. This repository contains the subset related just to the registry. |
How does this integrate with Docker engine?
This project should provide an implementation to a V2 API for use in the Docker
core project. The API should be embeddable
and simplify the process of securely pulling and pushing content from docker
daemons.
What are the long term goals of the Distribution project?
The Distribution project has the further long term goal of providing a secure tool chain for distributing content. The specifications, APIs and tools should be as useful with Docker as they are without.
Our goal is to design a professional grade and extensible content distribution system that allow users to:
- Enjoy an efficient, secured and reliable way to store, manage, package and exchange content
- Hack/roll their own on top of healthy open-source components
- Implement their own home made solution through good specs, and solid extensions mechanism.
More about Registry 2.0
The new registry implementation provides the following benefits:
- faster push and pull
- new, more efficient implementation
- simplified deployment
- pluggable storage backend
- webhook notifications
For information on upcoming functionality, please see ROADMAP.md.
Who needs to deploy a registry?
By default, Docker users pull images from Docker's public registry instance. Installing Docker gives users this ability. Users can also push images to a repository on Docker's public registry, if they have a Docker Hub account.
For some users and even companies, this default behavior is sufficient. For others, it is not.
For example, users with their own software products and may want to maintain an registry for private, company images. Also, you may wish to deploy your own image repository for images used to test or in continuous integration. For these use cases and others, deploying your own registry instance may be the better choice.
Contribute
Please see CONTRIBUTING.md for details on how to contribute issues, fixes, and patches to this project. If you are contributing code, see the instructions for building a development environment.
Support
If any issues are encountered while using the Distribution project, several avenues are available for support:
| IRC | #docker-distribution on FreeNode |
|---|---|
| Issue Tracker | github.com/docker/distribution/issues |
| Google Groups | https://groups.google.com/a/dockerproject.org/forum/#!forum/distribution |
| Mailing List | docker@dockerproject.org |
License
This project is distributed under Apache License, Version 2.0.