loco is a utility for bundling Docker registry credentials for Marathon. Marathon can pull images from private repositories but requires a fetch object with the bundled credentials. Rather than logging in using the docker cli and altering a developer's ~/.docker/config.json which may have have credentials to other registries, loco creates the directory and config file in memory, and generates a docker.tar.gz.

The uncompressed config file looks like this:

{
    "auths": {
        "https://index.docker.io/v1/": {  # or your index
            "auth": "<base64 encoded username:password>"
        }
    }
}

This file can then be uploaded to some filestore and served to the marathon process by adding a fetch object to the application definition.

{
    ...
    "fetch": [
        {
            "uri": "http://private.uri.com/docker.tar.gz",
            "extract": true
        }
    ]
}

go get -u github.com/micahhausler/loco
# or
docker pull micahhausler/loco

loco -h
Docker Login Compressor
Usage of ./loco:

  -o, --output string     The file to create. Use "-" for Stdout. (default "docker.tar.gz")
  -p, --password string   The password
  -r, --registry string   Specify a specific registry (default "https://index.docker.io/v1/")
  -u, --username string   The user to login as
      --version           print version and exit

MIT License. See License for full text