moby/api
Sebastiaan van Stijn 8aacbb3ba9
api: fix "GET /distribution" endpoint ignoring mirrors
If the daemon is configured to use a mirror for the default (Docker Hub)
registry, the endpoint did not fall back to querying the upstream if the mirror
did not contain the given reference.

If the daemon is configured to use a mirror for the default (Docker Hub)
registry, did not fall back to querying the upstream if the mirror did not
contain the given reference.

For pull-through registry-mirrors, this was not a problem, as in that case the
registry would forward the request, but for other mirrors, no fallback would
happen. This was inconsistent with how "pulling" images handled this situation;
when pulling images, both the mirror and upstream would be tried.

This problem was caused by the logic used in GetRepository, which had an
optimization to only return the first registry it was successfully able to
configure (and connect to), with the assumption that the mirror either contained
all images used, or to be configured as a pull-through mirror.

This patch:

- Introduces a GetRepositories method, which returns all candidates (both
  mirror(s) and upstream).
- Updates the endpoint to try all

Before this patch:

    # the daemon is configured to use a mirror for Docker Hub
    cat /etc/docker/daemon.json
    { "registry-mirrors": ["http://localhost:5000"]}

    # start the mirror (empty registry, not configured as pull-through mirror)
    docker run -d --name registry -p 127.0.0.1:5000:5000 registry:2

    # querying the endpoint fails, because the image-manifest is not found in the mirror:
    curl -s --unix-socket /var/run/docker.sock http://localhost/v1.43/distribution/docker.io/library/hello-world:latest/json
    {
      "message": "manifest unknown: manifest unknown"
    }

With this patch applied:

    # the daemon is configured to use a mirror for Docker Hub
    cat /etc/docker/daemon.json
    { "registry-mirrors": ["http://localhost:5000"]}

    # start the mirror (empty registry, not configured as pull-through mirror)
    docker run -d --name registry -p 127.0.0.1:5000:5000 registry:2

    # querying the endpoint succeeds (manifest is fetched from the upstream Docker Hub registry):
    curl -s --unix-socket /var/run/docker.sock http://localhost/v1.43/distribution/docker.io/library/hello-world:latest/json | jq .
    {
      "Descriptor": {
        "mediaType": "application/vnd.oci.image.index.v1+json",
        "digest": "sha256:1b9844d846ce3a6a6af7013e999a373112c3c0450aca49e155ae444526a2c45e",
        "size": 3849
      },
      "Platforms": [
        {
          "architecture": "amd64",
          "os": "linux"
        }
      ]
    }

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
2024-01-04 15:46:32 +01:00
..
server api: fix "GET /distribution" endpoint ignoring mirrors 2024-01-04 15:46:32 +01:00
templates/server swagger: fix "generated code" comment not in correct format 2019-11-05 11:32:37 -08:00
types api: Deprecate outdated fields in NetworkSettingsBase 2024-01-03 18:51:17 +01:00
common.go API: bump version to 1.44 2023-05-06 01:41:49 +02:00
README.md Include port in URL for locally built Swagger docs 2023-11-07 08:07:32 -05:00
swagger-gen.yaml Use a config to generate swagger api types 2016-10-31 11:13:41 -04:00
swagger.yaml api: Deprecate outdated fields in NetworkSettingsBase 2024-01-03 18:51:17 +01:00

Working on the Engine API

The Engine API is an HTTP API used by the command-line client to communicate with the daemon. It can also be used by third-party software to control the daemon.

It consists of various components in this repository:

  • api/swagger.yaml A Swagger definition of the API.
  • api/types/ Types shared by both the client and server, representing various objects, options, responses, etc. Most are written manually, but some are automatically generated from the Swagger definition. See #27919 for progress on this.
  • cli/ The command-line client.
  • client/ The Go client used by the command-line client. It can also be used by third-party Go programs.
  • daemon/ The daemon, which serves the API.

Swagger definition

The API is defined by the Swagger definition in api/swagger.yaml. This definition can be used to:

  1. Automatically generate documentation.
  2. Automatically generate the Go server and client. (A work-in-progress.)
  3. Provide a machine readable version of the API for introspecting what it can do, automatically generating clients for other languages, etc.

Updating the API documentation

The API documentation is generated entirely from api/swagger.yaml. If you make updates to the API, edit this file to represent the change in the documentation.

The file is split into two main sections:

  • definitions, which defines re-usable objects used in requests and responses
  • paths, which defines the API endpoints (and some inline objects which don't need to be reusable)

To make an edit, first look for the endpoint you want to edit under paths, then make the required edits. Endpoints may reference reusable objects with $ref, which can be found in the definitions section.

There is hopefully enough example material in the file for you to copy a similar pattern from elsewhere in the file (e.g. adding new fields or endpoints), but for the full reference, see the Swagger specification.

swagger.yaml is validated by hack/validate/swagger to ensure it is a valid Swagger definition. This is useful when making edits to ensure you are doing the right thing.

Viewing the API documentation

When you make edits to swagger.yaml, you may want to check the generated API documentation to ensure it renders correctly.

Run make swagger-docs and a preview will be running at http://localhost:9000. Some of the styling may be incorrect, but you'll be able to ensure that it is generating the correct documentation.

The production documentation is generated by vendoring swagger.yaml into docker/docker.github.io.