Crane is a small read-only web application that provides enough of the docker registry API to support "docker pull". Crane does not serve the actual image files, but instead serves 302 redirects to some other location where files are being served. A base file location URL can be specified per-repository.

Crane loads its data from json files stored on disk. It does not have a database or use any other services. The json files can be generated with pulp by publishing a docker repository.

Crane is a flask app written in Python. It is very easy to deploy and has a small footprint, so it is a great way to provide a read-only "docker pull" API that redirects to a static file service.

Advanced users can configure a search appliance to support "docker search" and can setup repository protection using SSL certificates.

A config file will be loaded from the path found in environment variable CRANE_CONFIG_PATH. If not specified, the default location of /etc/crane.conf will be used.

The following options should go under a section named [general]

debug

true or false, which sets Flask's DEBUG config option. Defaults to false. If the environment variable CRANE_DEBUG has the value true, that will also put crane in debug mode regardless of the setting in the config file.

data_dir

full path to the directory from which metadata files should be loaded. defaults to /var/lib/crane/metadata/

data_dir_polling_interval

The number of seconds between checks for updates to metadata files in the data_dir. This defaults to checking once every 60 seconds.

endpoint

hostname and optional port, in the form hostname:port, where crane is deployed. This is the value that will be returned for the X-Docker-Endpoint header. defaults to the host and port used by the requesting client

Example:

[general]
debug: true
data_dir: /mnt/nfs/
endpoint: localhost:5000

Only one of the following search backends should be configured. If multiple backends are configured, crane will attempt to use the first one whose configuration it finds, and the discovery order is not guaranteed to be consistent.

The API supporting docker search can be enabled by configuring a Google Search Appliance for use by crane. In crane's configuration file, a section [gsa] must exist with key url. The URL will be used in a GET request, and a query parameter q will be added with a search term.

Example:

[gsa]
url: https://path/to/my/search?x=1&y=2

The XML returned by the GSA must contain values for portal_name and portal_short_description, which will be turned into the name and description returned by crane's search API.

The API supporting docker search can be enabled by configuring a Solr deployment for use by crane. In crane's configuration file, a section [solr] must exist with key url. The URL will be used in a GET request, and it must contain the string {0} as a placeholder where the search string will be inserted.

Example:

[solr]
url: https://path/to/my/search?x={0}

The JSON returned by the request must contain the following minimum data structure. ir_automated, ir_official, and ir_stars are optional and will default to False, False, and 0 respectively.

{
  "response": {
    "docs": [
      {
        "allTitle": "pulp/worker",
        "ir_description": "A short description to display in the terminal",
        "ir_automated": true,
        "ir_official": true,
        "ir_stars": 7
      }
    ]
  }
}

Sample apache configuration files are available in /usr/share/crane/ when installed via RPM, or in the deployment/ directory if looking at the source. You can copy one of them into your apache conf.d directory and optionally modify it to fit your needs.

To change what data crane is using, add or remove files in the configured data_dir as necessary. The changes will be loaded automatically the next time the data_dir is polled for changes. This poll runs at the interval set by data_dir_polling_interval. Auto loading of changes monitors file creation and deletion. If a file is modified in place you may have to restart the web server in order for the change to be loaded.

Crane expects to find files in the configured data_dir whose names end in .json. Nothing else about the file names is important to crane. Each file contains metadata about a docker repository.

These files are produced by a publish action in Pulp.

A list of images served by Crane can be obtained by opening /crane/repositories in a web browser or with curl. The default Apache configuration distributed with Crane restricts access to this URL from localhost only; when accessed from a web browser, repositories and their images are listed on a web page. This URL accepts an optional "Accept" header. When "application/json" is specified, the application responds with JSON. Here is an example:

{
    "pulpdemo-busybox": {
        "image_ids": [
            "2982ec56c8d910121e7594ca7890b062f6d37fadf7575f6a6f3adbabbafac9f5",
            "2aed48a4e41d3931167146e9b7492aa5639e7f6478be9eac584726ecec6824ed",
            "492dad4279bae5bb73648efe9bf467b2cfa8bab1d593595226e3e7a95d9f6c35",
            "4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125",
            "511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158",
            "618b1fc306b06d11e192812ede4c685dcbf886d2a0189e9a552c550fd7663df0",
            "df7546f9f060a2268024c8a230d8639878585defcc1bc6f79d2728a13957871b",
            "e8a999563c473139dc74d02eefb7b13ffea63799bc05b8936b9ad7119b37742f",
            "ea13149945cb6b1e746bf28032f02e9b5a793523481a0a18645fc77ad53c4ea2",
            "f6169d24347d30de48e4493836bec15c78a34f08cc7f17d6a45a19d68dc283ac"
        ],
        "protected": false,
        "tags": {
            "buildroot-2013.08.1": "2982ec56c8d910121e7594ca7890b062f6d37fadf7575f6a6f3adbabbafac9f5",
            "buildroot-2014.02": "2aed48a4e41d3931167146e9b7492aa5639e7f6478be9eac584726ecec6824ed",
            "latest": "4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125",
            "ubuntu-12.04": "492dad4279bae5bb73648efe9bf467b2cfa8bab1d593595226e3e7a95d9f6c35",
            "ubuntu-14.04": "f6169d24347d30de48e4493836bec15c78a34f08cc7f17d6a45a19d68dc283ac"
        }
    },
    "pulpdemo-busybox2": {
        "image_ids": [
            "2982ec56c8d910121e7594ca7890b062f6d37fadf7575f6a6f3adbabbafac9f5",
            "2aed48a4e41d3931167146e9b7492aa5639e7f6478be9eac584726ecec6824ed",
            "492dad4279bae5bb73648efe9bf467b2cfa8bab1d593595226e3e7a95d9f6c35",
            "4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125",
            "511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158",
            "618b1fc306b06d11e192812ede4c685dcbf886d2a0189e9a552c550fd7663df0",
            "df7546f9f060a2268024c8a230d8639878585defcc1bc6f79d2728a13957871b",
            "e8a999563c473139dc74d02eefb7b13ffea63799bc05b8936b9ad7119b37742f",
            "ea13149945cb6b1e746bf28032f02e9b5a793523481a0a18645fc77ad53c4ea2",
            "f6169d24347d30de48e4493836bec15c78a34f08cc7f17d6a45a19d68dc283ac"
        ],
        "protected": false,
        "tags": {
            "buildroot-2013.08.1": "2a4d48a4e51d39a1167146e9b7492aa5639e7f6478be9eac584726ecec6824ed",
            "latest": "4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125",
            "ubuntu-12.04": "492dad4279bae5bb73648efe9bf467b2cfa8bab1d593595226e3e7a95d9f6c35",
            "ubuntu-14.04": "f6169d24347d30de48e4493836bec15c78a34f08cc7f17d6a45a19d68dc283ac"
        }
    }
}

Basic username/passphrase authentication may be configured using standard Apache configuration. End-users access images by client command docker login <crane-registry-uri>. End-users who docker pull <image> before logging in will be prompted for usernamd/passphrase.

Crane does not manage users. They must be managed with an .htpasswd file. The htpasswd tool is available to manage the .htpasswd file. See Apache documentation.

Configuration may be enabled through an Apache config or .htaccess file. See Apache documentation.

Example .htaccess file:

AuthType Basic
AuthName "Authentication Required"
AuthUserFile /path/to/.htpasswd
Require valid-user

Example apache.conf file:

<VirtualHost *>
    WSGIScriptAlias / /usr/share/crane/crane.wsgi
    <Location /crane>
        Require host localhost
        AuthType Basic
        AuthName "Docker Registry Repository"
        AuthUserFile /path/to/.htpasswd
        Require valid-user
    </Location>
</VirtualHost>

The image of the crane displayed in the corner of the web interface is used with permission from user Laitche under Creative Commons Attribution-Share Alike 3.0 Unported licence. The original file can be found here.