page_title: Registry Documentation page_description: Documentation for docker Registry and Registry API page_keywords: docker, registry, api, hub

The Docker Hub and the Registry 1.0 spec

The three roles

There are three major components playing a role in the Docker ecosystem.

Docker Hub

The Docker Hub is responsible for centralizing information about:

• User accounts
• Checksums of the images
• Public namespaces

The Docker Hub has different components:

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

The Docker Hub is authoritative for that information.

There is only one instance of the Docker Hub, run and managed by Docker Inc.

Docker Registry 1.0

The 1.0 registry has the following characteristics:

• 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 Docker Hub 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 you 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 Docker, Inc. It features read/write access, and delegates authentication and authorization to the Docker Hub.
• 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 Docker Hub. 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., vendors 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 Docker's control. It can optionally delegate additional authorization to the Docker Hub, but it is not mandatory.

Note: The latter implies that while HTTP is the protocol of choice for a registry, multiple schemes are possible (and in some cases, trivial):

• HTTP with GET (and PUT for read-write registries);
• local mount point;
• remote docker addressed through SSH.

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).

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 Docker Hub

Workflow

Pull

1. Contact the Docker Hub to know where I should download “samalba/busybox”
2. Docker Hub 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 Docker Hub to verify if token/user is allowed to download images
5. Docker Hub 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:

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

In this case, Docker bypasses the Docker Hub. 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.

API (pulling repository foo/bar):

1. (Docker -> Docker Hub) GET /v1/repositories/foo/bar/images:

Headers:

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

Action:

    (looking up the foo/bar in db and gets images and checksums
    for that repo (all if no tag is specified, if tag, only
    checksums for those tags) see part 4.4.1)

2. (Docker Hub -> Docker) HTTP 200 OK

Headers:

    Authorization: Token
    signature=123abc,repository=”foo/bar”,access=write
    X-Docker-Endpoints: registry.docker.io [,registry2.docker.io]

Body:

    Jsonified checksums (see part 4.4.1)

3. (Docker -> Registry) GET /v1/repositories/foo/bar/tags/latest

Headers:

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

4. (Registry -> Docker Hub) GET /v1/repositories/foo/bar/images

Headers:

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

Body:

    <ids and checksums in payload>

Action:

    (Lookup token see if they have access to pull.)

    If good:
    HTTP 200 OK Docker Hub will invalidate the token

    If bad:
    HTTP 401 Unauthorized

5. (Docker -> Registry) GET /v1/images/928374982374/ancestry

Action:

    (for each image id returned in the registry, fetch /json + /layer)

Note: If someone makes a second request, then we will always give a new token, never reuse tokens.

Push

1. Contact the Docker Hub 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 Docker Hub)
3. Push the image on the registry (along with the token)
4. Registry A contacts the Docker Hub to verify the token (token must corresponds to the repository name)
5. Docker Hub validates the token. Registry A starts reading the stream pushed by docker and store the repository (with its images)
6. docker contacts the Docker Hub to give checksums for upload images

Note: It's possible not to use the Docker Hub at all! In this case, a deployed version of the Registry is deployed to store and serve images. Those images are not authenticated and the security is not guaranteed.

Note: Docker Hub can be replaced! For a private Registry deployed, a custom Docker Hub can be used to serve and validate token according to different policies.

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

API (pushing repos foo/bar):

1. (Docker -> Docker Hub) PUT /v1/repositories/foo/bar/

Headers:

    Authorization: Basic sdkjfskdjfhsdkjfh== X-Docker-Token:
    true

Action:

• in Docker Hub, we allocated a new repository, and set to initialized

Body:

(The body contains the list of images that are going to be pushed, with empty checksums. The checksums will be set at the end of the push):

    [{“id”: “9e89cc6f0bc3c38722009fe6857087b486531f9a779a0c17e3ed29dae8f12c4f”}]

2. (Docker Hub -> Docker) 200 Created

Headers:

    WWW-Authenticate: Token
    signature=123abc,repository=”foo/bar”,access=write
    X-Docker-Endpoints: registry.docker.io [, registry2.docker.io]

3. (Docker -> Registry) PUT /v1/images/98765432_parent/json

Headers:

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

4. (Registry->Docker Hub) GET /v1/repositories/foo/bar/images

Headers:

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

Action:

• Docker Hub: will invalidate the token.
• Registry: grants a session (if token is approved) and fetches the images id

5. (Docker -> Registry) PUT /v1/images/98765432_parent/json

Headers:

    Authorization: Token
    signature=123abc,repository=”foo/bar”,access=write
    Cookie: (Cookie provided by the Registry)

6. (Docker -> Registry) PUT /v1/images/98765432/json

Headers:

    Cookie: (Cookie provided by the Registry)

7. (Docker -> Registry) PUT /v1/images/98765432_parent/layer

Headers:

    Cookie: (Cookie provided by the Registry)

8. (Docker -> Registry) PUT /v1/images/98765432/layer

Headers:

    X-Docker-Checksum: sha256:436745873465fdjkhdfjkgh

9. (Docker -> Registry) PUT /v1/repositories/foo/bar/tags/latest

Headers:

    Cookie: (Cookie provided by the Registry)

Body:

    “98765432”

10. (Docker -> Docker Hub) PUT /v1/repositories/foo/bar/images

Headers:

    Authorization: Basic 123oislifjsldfj== X-Docker-Endpoints:
    registry1.docker.io (no validation on this right now)

Body:

    (The image, id`s, tags and checksums)
    [{“id”:
    “9e89cc6f0bc3c38722009fe6857087b486531f9a779a0c17e3ed29dae8f12c4f”,
    “checksum”:
    “b486531f9a779a0c17e3ed29dae8f12c4f9e89cc6f0bc3c38722009fe6857087”}]

Return:

    HTTP 204

Note: If push fails and they need to start again, what happens in the Docker Hub, there will already be a record for the namespace/name, but it will be initialized. Should we allow it, or mark as name already used? One edge case could be if someone pushes the same thing at the same time with two different shells.

If it‘s a retry on the Registry, Docker has a cookie (provided by the registry after token validation). So the Docker Hub won’t have to provide a new token.

Delete

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

1. Docker contacts the Docker Hub 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 Docker Hub to verify the token (token must corresponds to the repository name)
5. Docker Hub validates the token. Registry A deletes the repository and everything associated to it.
6. docker contacts the Docker Hub to let it know it was removed from the registry, the Docker Hub removes all records from the database.

Note: The Docker client should present an “Are you sure?” prompt to confirm the deletion before starting the process. Once it starts it can't be undone.

API (deleting repository foo/bar):

1. (Docker -> Docker Hub) DELETE /v1/repositories/foo/bar/

Headers:

    Authorization: Basic sdkjfskdjfhsdkjfh== X-Docker-Token:
    true

Action:

• in Docker Hub, we make sure it is a valid repository, and set to deleted (logically)

Body:

    Empty

2. (Docker Hub -> Docker) 202 Accepted

Headers:

    WWW-Authenticate: Token
    signature=123abc,repository=”foo/bar”,access=delete
    X-Docker-Endpoints: registry.docker.io [, registry2.docker.io]
    # list of endpoints where this repo lives.

3. (Docker -> Registry) DELETE /v1/repositories/foo/bar/

Headers:

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

4. (Registry->Docker Hub) PUT /v1/repositories/foo/bar/auth

Headers:

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

Action:

• Docker Hub: will invalidate the token.
• Registry: deletes the repository (if token is approved)

5. (Registry -> Docker) 200 OK

   200 If success 403 if forbidden 400 if bad request 404
   if repository isn't found
   

6. (Docker -> Docker Hub) DELETE /v1/repositories/foo/bar/

Headers:

    Authorization: Basic 123oislifjsldfj== X-Docker-Endpoints:
    registry-1.docker.io (no validation on this right now)

Body:

    Empty

Return:

    HTTP 200

How to use the Registry in standalone mode

The Docker Hub has two main purposes (along with its fancy social features):

• Resolve short names (to avoid passing absolute URLs all the time):

  username/projectname -> https://registry.docker.io/users//repositories// team/projectname -> https://registry.docker.io/team//repositories//

• Authenticate a user as a repos owner (for a central referenced repository)

Without a Docker Hub

Using the Registry without the Docker Hub 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? ne? -no-index?). In this mode, the only thing which changes is that Registry will never contact the Docker Hub 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).

With a Docker Hub

The Docker Hub 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 Docker Hub.

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

The API

The first version of the api is available here: https://github.com/jpetazzo/docker/blob/acd51ecea8f5d3c02b00a08176171c59442df8b3/docs/images-repositories-push-pull.md

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

Users

Create a user (Docker Hub)

POST /v1/users:

Body:

{"email": "[sam@docker.com](mailto:sam%40docker.com)",
"password": "toto42", "username": "foobar"`}

Validation:

• username: min 4 character, max 30 characters, must match the regular expression [a-z0-9_].
• password: min 5 characters

Valid:

 return HTTP 201

Errors: HTTP 400 (we should create error codes for possible errors) - invalid json - missing field - wrong format (username, password, email, etc) - forbidden name - name already exists

Note: A user account will be valid only if the email has been validated (a validation link is sent to the email address).

Update a user (Docker Hub)

PUT /v1/users/<username>

Body:

{"password": "toto"}

Note: We can also update email address, if they do, they will need to reverify their new email address.

Login (Docker Hub)

Does nothing else but asking for a user authentication. Can be used to validate credentials. HTTP Basic Auth for now, maybe change in future.

GET /v1/users

Return:

• Valid: HTTP 200
• Invalid login: HTTP 401
• Account inactive: HTTP 403 Account is not Active

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-_.]

Get all tags:

GET /v1/repositories/<namespace>/<repository_name>/tags

**Return**: HTTP 200
[
    {
        "layer": "9e89cc6f",
        "name": "latest"
    },
    {
        "layer": "b486531f",
        "name": "0.1.1",
    }
]

4.3.2 Read the content of a tag (resolve the image id):

GET /v1/repositories/<namespace>/<repo_name>/tags/<tag>

Return:

"9e89cc6f0bc3c38722009fe6857087b486531f9a779a0c17e3ed29dae8f12c4f"

4.3.3 Delete a tag (registry):

DELETE /v1/repositories/<namespace>/<repo_name>/tags/<tag>

4.4 Images (Docker Hub)

For the Docker Hub 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.

4.4.1 Get the images:

GET /v1/repositories/<namespace>/<repo_name>/images

**Return**: HTTP 200
[{“id”:
“9e89cc6f0bc3c38722009fe6857087b486531f9a779a0c17e3ed29dae8f12c4f”,
“checksum”:
“[md5:b486531f9a779a0c17e3ed29dae8f12c4f9e89cc6f0bc3c38722009fe6857087](md5:b486531f9a779a0c17e3ed29dae8f12c4f9e89cc6f0bc3c38722009fe6857087)”}]

Add/update the images:

You always add images, you never remove them.

PUT /v1/repositories/<namespace>/<repo_name>/images

Body:

[ {“id”:
“9e89cc6f0bc3c38722009fe6857087b486531f9a779a0c17e3ed29dae8f12c4f”,
“checksum”:
“sha256:b486531f9a779a0c17e3ed29dae8f12c4f9e89cc6f0bc3c38722009fe6857087”}
]

Return:

204

Repositories

Remove a Repository (Registry)

DELETE /v1/repositories//<repo_name>

Return 200 OK

Remove a Repository (Docker Hub)

This starts the delete process. see 2.3 for more details.

DELETE /v1/repositories//<repo_name>

Return 202 OK

Chaining Registries

It's possible to chain Registries server for several reasons:

• Load balancing
• Delegate the next request to another server

When a Registry is a reference for a repository, it should host the entire images chain in order to avoid breaking the chain during the download.

The Docker Hub and Registry use this mechanism to redirect on one or the other.

Example with an image download:

On every request, a special header can be returned:

X-Docker-Endpoints: server1,server2

On the next request, the client will always pick a server from this list.

Authentication & Authorization

On the Docker Hub

The Docker Hub supports both “Basic” and “Token” challenges. Usually when there is a 401 Unauthorized, the Docker Hub 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="

Document Version

• 1.0 : May 6th 2013 : initial release
• 1.1 : June 1st 2013 : Added Delete Repository and way to handle new source namespace.