docker-credential-gcr

docker-credential-gcr

Introduction

docker-credential-gcr is Google Container Registry's standalone, gcloud SDK-independent Docker credential helper. It allows for Docker clients since v1.11 to easily make authenticated requests to GCR's repositories (gcr.io, eu.gcr.io, etc.).

Note: docker-credential-gcr is primarily intended for users wishing to authenticate with GCR in the absence of gcloud, though they are not mutually exclusive. For normal development setups, users are encouraged to use gcloud auth configure-docker, instead.

The helper implements the Docker Credential Store API, but enables more advanced authentication schemes for GCR's users. In particular, it respects Application Default Credentials and is capable of generating credentials automatically (without an explicit login operation) when running in App Engine or Compute Engine.

For even more authentication options, see GCR's documentation on advanced authentication methods.

GCR Credentials

By default, the helper searches for GCR credentials in the following order:

1. In the helper's private credential store (i.e. those stored via docker-credential-gcr gcr-login)
2. From the gcloud SDK (i.e. the one printed via gcloud config config-helper --force-auth-refresh --format='value(credential.access_token)').
3. In a JSON file whose path is specified by the GOOGLE_APPLICATION_CREDENTIALS environment variable.
4. In a JSON file in a location known to the helper:
   • On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
   • On other systems, $HOME/.config/gcloud/application_default_credentials.json.
5. On Google App Engine, it uses the appengine.AccessToken function.
6. On Google Compute Engine, Kubernetes Engine, and App Engine Managed VMs, it fetches the credentials of the service account associated with the VM from the metadata server (if available).

Users may limit or re-order how the helper searches for GCR credentials using docker-credential-gcr config --token-source. Number 1 above is designated by the store, 2 by gcloud, and 3-6 by env (which cannot be individually restricted or re-ordered). Multiple sources are separated by commas, and the default is "store, gcloud, env".

Examples:

To configure the credential helper to use only the gcloud SDK's access token:

docker-credential-gcr config --token-source="gcloud"

To try the private store, followed by the environment:

docker-credential-gcr config --token-source="store, env"

To verify that credentials are being returned for a given registry, e.g. for https://gcr.io:

echo "https://gcr.io" | docker-credential-gcr get

Other Credentials

The helper implements the Docker Credential Store API and can be used to store credentials for other repositories. WARNING: Credentials are stored in plain text in a file under the user's home directory (e.g. $HOME/.config/gcloud/docker_credentials.json on non-windows systems).

Building from Source

The program in this repository is written with the Go programming language and built with make. These instructions assume that Go 1.7+ and make are installed on a *nix system.

You can download the source code, compile the binary, and put it in your $GOPATH with go get.

go get -u github.com/GoogleCloudPlatform/docker-credential-gcr

If $GOPATH/bin is in your system $PATH, this will also automatically install the compiled binary. You can confirm using which docker-credential-gcr and continue to the section on Configuration and Usage.

Alternatively, you can use make to build the program. The executable will be output to the bin directory inside the repository.

cd $GOPATH/src/github.com/GoogleCloudPlatform/docker-credential-gcr
make

Then, you can put that binary in your $PATH to make it visible to docker. For example, if /usr/bin is present in your system path:

sudo mv ./bin/docker-credential-gcr /usr/bin/docker-credential-gcr

Configuration and Usage

• Configure the Docker CLI to use docker-credential-gcr as its credential store:

  docker-credential-gcr configure-docker
  

  • Alternatively, use the manual configuration instructions below to configure your version of the Docker client.

• Log in to GCR (or don't! See the GCR Credentials section)

  docker-credential-gcr gcr-login
  

• Use Docker!

  docker pull gcr.io/project-id/neato-container
  

• Log out from GCR

  docker-credential-gcr gcr-logout
  

Manual Docker Client Configuration

(Recommended) Using credHelpers, for Docker clients since v1.13.0

Add a credHelpers entry in the Docker config file (usually ~/.docker/config.json on OSX and Linux, %USERPROFILE%\.docker\config.json on Windows) for each GCR registry that you care about. The key should be the domain of the registry (without the "https://") and the key should be the suffix of the credential helper binary (everything after "docker-credential-").

e.g. for `docker-credential-gcr`:

    {
      "auths" : {
            ...
      }
      "credHelpers": {
            "coolregistry.com": ... ,
            "gcr.io": "gcr",
            "asia.gcr.io": "gcr",
            ...
      },
      "HttpHeaders": ...
      "psFormat": ...
      "imagesFormat": ...
      "detachKeys": ...
    }
  

Using the credsStore, for Docker clients since v1.11.0

Set the credsStore and auths fields in your Docker config file (usually ~/.docker/config.json on OSX and Linux, %USERPROFILE%\.docker\config.json on Windows). The value of credsStore should be the suffix of the compiled binary (everything after "docker-credential-") and auths should have an empty entry for each GCR endpoint that you care about (with the "https://").

e.g. for `docker-credential-gcr`:

    {
      "auths": {
            "https://coolregistry.com": { ... },
            "https://gcr.io": {},
            "https://asia.gcr.io": {},
            ...
      },
      "credsStore": "gcr",
      "HttpHeaders": ...
      "psFormat": ...
      "imagesFormat": ...
      "detachKeys": ...
    }
  

License

Apache 2.0. See LICENSE for more information.