Registry & Index Spec

1.1 Index¶

The Index is responsible for centralizing information about:

• User accounts
• Checksums of the images
• Public namespaces

The Index has different components:

• Web UI
• Meta-data store (comments, stars, list public repositories)
• Authentication service
• Tokenization

The index is authoritative for those information.

We expect that there will be only one instance of the index, run and managed by Docker Inc.

1.2 Registry¶

• It stores the images and the graph for a set of repositories
• It does not have user accounts data
• It has no notion of user accounts or authorization
• It delegates authentication and authorization to the Index Auth service using tokens
• It supports different storage backends (S3, cloud files, local FS)
• It doesn’t have a local database
• Source Code

We expect that there will be multiple registries out there. To help to grasp the context, here are some examples of registries:

• sponsor registry: such a registry is provided by a third-party hosting infrastructure as a convenience for their customers and the docker community as a whole. Its costs are supported by the third party, but the management and operation of the registry are supported by dotCloud. It features read/write access, and delegates authentication and authorization to the Index.
• mirror registry: such a registry is provided by a third-party hosting infrastructure but is targeted at their customers only. Some mechanism (unspecified to date) ensures that public images are pulled from a sponsor registry to the mirror registry, to make sure that the customers of the third-party provider can “docker pull” those images locally.
• vendor registry: such a registry is provided by a software vendor, who wants to distribute docker images. It would be operated and managed by the vendor. Only users authorized by the vendor would be able to get write access. Some images would be public (accessible for anyone), others private (accessible only for authorized users). Authentication and authorization would be delegated to the Index. The goal of vendor registries is to let someone do “docker pull basho/riak1.3” and automatically push from the vendor registry (instead of a sponsor registry); i.e. get all the convenience of a sponsor registry, while retaining control on the asset distribution.
• private registry: such a registry is located behind a firewall, or protected by an additional security layer (HTTP authorization, SSL client-side certificates, IP address authorization...). The registry is operated by a private entity, outside of dotCloud’s control. It can optionally delegate additional authorization to the Index, but it is not mandatory.

The latter would only require two new commands in docker, e.g. registryget and registryput, wrapping access to the local filesystem (and optionally doing consistency checks). Authentication and authorization are then delegated to SSH (e.g. with public keys).

1.3 Docker¶

On top of being a runtime for LXC, Docker is the Registry client. It supports:

• Push / Pull on the registry
• Client authentication on the Index

2.1 Pull¶

1. Contact the Index to know where I should download “samalba/busybox”
2. Index replies: a. samalba/busybox is on Registry A b. here are the checksums for samalba/busybox (for all layers) c. token
3. Contact Registry A to receive the layers for samalba/busybox (all of them to the base image). Registry A is authoritative for “samalba/busybox” but keeps a copy of all inherited layers and serve them all from the same location.
4. registry contacts index to verify if token/user is allowed to download images
5. Index returns true/false lettings registry know if it should proceed or error out
6. Get the payload for all layers

It’s possible to run:

docker pull https://<registry>/repositories/samalba/busybox

In this case, Docker bypasses the Index. However the security is not guaranteed (in case Registry A is corrupted) because there won’t be any checksum checks.

Currently registry redirects to s3 urls for downloads, going forward all downloads need to be streamed through the registry. The Registry will then abstract the calls to S3 by a top-level class which implements sub-classes for S3 and local storage.

Token is only returned when the X-Docker-Token header is sent with request.

Basic Auth is required to pull private repos. Basic auth isn’t required for pulling public repos, but if one is provided, it needs to be valid and for an active account.

2.2 Push¶

1. Contact the index to allocate the repository name “samalba/busybox” (authentication required with user credentials)
2. If authentication works and namespace available, “samalba/busybox” is allocated and a temporary token is returned (namespace is marked as initialized in index)
3. Push the image on the registry (along with the token)
4. Registry A contacts the Index to verify the token (token must corresponds to the repository name)
5. Index validates the token. Registry A starts reading the stream pushed by docker and store the repository (with its images)
6. docker contacts the index to give checksums for upload images

Docker computes the checksums and submit them to the Index at the end of the push. When a repository name does not have checksums on the Index, it means that the push is in progress (since checksums are submitted at the end).

2.3 Delete¶

If you need to delete something from the index or registry, we need a nice clean way to do that. Here is the workflow.

1. Docker contacts the index to request a delete of a repository samalba/busybox (authentication required with user credentials)
2. If authentication works and repository is valid, samalba/busybox is marked as deleted and a temporary token is returned
3. Send a delete request to the registry for the repository (along with the token)
4. Registry A contacts the Index to verify the token (token must corresponds to the repository name)
5. Index validates the token. Registry A deletes the repository and everything associated to it.
6. docker contacts the index to let it know it was removed from the registry, the index removes all records from the database.

3.1 Without an Index¶

Using the Registry without the Index can be useful to store the images on a private network without having to rely on an external entity controlled by Docker Inc.

In this case, the registry will be launched in a special mode (–standalone? –no-index?). In this mode, the only thing which changes is that Registry will never contact the Index to verify a token. It will be the Registry owner responsibility to authenticate the user who pushes (or even pulls) an image using any mechanism (HTTP auth, IP based, etc...).

In this scenario, the Registry is responsible for the security in case of data corruption since the checksums are not delivered by a trusted entity.

As hinted previously, a standalone registry can also be implemented by any HTTP server handling GET/PUT requests (or even only GET requests if no write access is necessary).

3.2 With an Index¶

The Index data needed by the Registry are simple:

• Serve the checksums
• Provide and authorize a Token

In the scenario of a Registry running on a private network with the need of centralizing and authorizing, it’s easy to use a custom Index.

The only challenge will be to tell Docker to contact (and trust) this custom Index. Docker will be configurable at some point to use a specific Index, it’ll be the private entity responsibility (basically the organization who uses Docker in a private environment) to maintain the Index and the Docker’s configuration among its consumers.

4.1 Images¶

The format returned in the images is not defined here (for layer and JSON), basically because Registry stores exactly the same kind of information as Docker uses to manage them.

The format of ancestry is a line-separated list of image ids, in age order, i.e. the image’s parent is on the last line, the parent of the parent on the next-to-last line, etc.; if the image has no parent, the file is empty.

GET /v1/images/<image_id>/layer
PUT /v1/images/<image_id>/layer
GET /v1/images/<image_id>/json
PUT /v1/images/<image_id>/json
GET /v1/images/<image_id>/ancestry
PUT /v1/images/<image_id>/ancestry

4.2 Users¶

4.3 Tags (Registry)¶

The Registry does not know anything about users. Even though repositories are under usernames, it’s just a namespace for the registry. Allowing us to implement organizations or different namespaces per user later, without modifying the Registry’s API.

The following naming restrictions apply:

• Namespaces must match the same regular expression as usernames (See 4.2.1.)
• Repository names must match the regular expression [a-zA-Z0-9-_.]

4.4 Images (Index)¶

For the Index to “resolve” the repository name to a Registry location, it uses the X-Docker-Endpoints header. In other terms, this requests always add a X-Docker-Endpoints to indicate the location of the registry which hosts this repository.

4.5 Repositories¶

6.1 On the Index¶

The Index supports both “Basic” and “Token” challenges. Usually when there is a 401 Unauthorized, the Index replies this:

401 Unauthorized
WWW-Authenticate: Basic realm="auth required",Token

You have 3 options:

1. Provide user credentials and ask for a token

   Header:

   • Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
   • X-Docker-Token: true

   In this case, along with the 200 response, you’ll get a new token (if user auth is ok): If authorization isn’t correct you get a 401 response. If account isn’t active you will get a 403 response.

   Response:

   • 200 OK
   • X-Docker-Token: Token signature=123abc,repository=”foo/bar”,access=read

2. Provide user credentials only

   Header:

   Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

3. Provide Token

   Header:

   Authorization: Token signature=123abc,repository=”foo/bar”,access=read

6.2 On the Registry¶

The Registry only supports the Token challenge:

401 Unauthorized
WWW-Authenticate: Token

The only way is to provide a token on 401 Unauthorized responses:

Authorization: Token signature=123abc,repository="foo/bar",access=read

Usually, the Registry provides a Cookie when a Token verification succeeded. Every time the Registry passes a Cookie, you have to pass it back the same cookie.:

200 OK
Set-Cookie: session="wD/J7LqL5ctqw8haL10vgfhrb2Q=?foo=UydiYXInCnAxCi4=&timestamp=RjEzNjYzMTQ5NDcuNDc0NjQzCi4="; Path=/; HttpOnly

Next request:

GET /(...)
Cookie: session="wD/J7LqL5ctqw8haL10vgfhrb2Q=?foo=UydiYXInCnAxCi4=&timestamp=RjEzNjYzMTQ5NDcuNDc0NjQzCi4="