Image Authorization Plugin for Docker

The problem to be solved: you want to make sure that your container infrastructure (in the cloud or at the edge), only accepts signed Docker images from a specific Docker registry.

SixSq’s Image Authorization Plugin is a Docker Plugin which makes sure all Docker Registry-related requests are limited to trusted Docker images only, from a user-specified Docker Registry endpoint.

Docker and Notary tools are used to enforce and verify the Docker Registry and Image verification workflows.



The plugin needs the configuration variables: REGISTRY, NOTARY and NOTARY_ROOT_CA. If you leave those empty, the plugin defaults to and

  • REGISTRY: is the host:port of the registry to be authorized
  • NOTARY: is the https://fqdn:port of the Notary server used for signing the images
  • NOTARY_ROOT_CA: is the raw public Certificate Authority certificate used for the Notary server TLS certificates

You can either install the plugin from source, or from Docker Hub.

NOTE: please note that the plugin is architecture specific. Therefore, from hereon, is the target device's CPU architecture.

From source

To install the plugin from the repo:

make local_install REGISTRY=<registry> NOTARY=<notary-server> NOTARY_ROOT_CA='''<raw-ca-cert>'''

(if you’ve already run make build and make create, then you can simply run make enable REGISTRY=<registry> ...).

Add the following JSON key value to /etc/docker/daemon.json:

"authorization-plugins": ["sixsq/img-authz-plugin:<YOUR_CPU_ARCH>"]

and run kill -SIGHUP $(pidof dockerd)

From a Docker registry

Only available for x86_64 and aarch64 CPU architectures!

To get and install the plugin, simply run:

docker plugin install sixsq/img-authz-plugin:<YOUR_CPU_ARCH> REGISTRY=<registry> NOTARY=<notary-server> NOTARY_ROOT_CA='''<raw-ca-cert>'''

NOTE: you’ll be prompted with some special access requests for the plugin (like access to the host network). Please reply y otherwise the plugin will not function correctly. If you’d like to avoid being prompted, you can run the command from above with --grant-all-permissions.

Add the following JSON key value to /etc/docker/daemon.json:

"authorization-plugins": ["sixsq/img-authz-plugin:<YOUR_CPU_ARCH>"]

and run kill -SIGHUP $(pidof dockerd)

Update the registries in a running plugin

First disable the plugin:

docker plugin disable sixsq/img-authz-plugin:<YOUR_CPU_ARCH>

Then set the new registries value:

docker plugin set sixsq/img-authz-plugin:<YOUR_CPU_ARCH> REGISTRY=<registry> NOTARY=<notary-server> NOTARY_ROOT_CA='''<raw-ca-cert>'''

Re-enable the plugin, and reload the Docker daemon:

docker plugin enable sixsq/img-authz-plugin:<YOUR_CPU_ARCH> && kill -SIGHUP $(pidof dockerd)

Using a self-signed private registry

If you’re using a private Docker registry with self-signed TLS certificates, please remember to add the client certificates to your Docker trust directory.

To do this, please follow the steps here.

NOTE: using insecure Docker registries (without TLS) is not recommended and thus not covered by this plugin. Use it at your own risk.

Plugin logs

The plugin logs are appended to the Docker daemon logs, and thus you can find them in your respective Docker logs’ directory (for example, for Ubuntu you can do journal -u docker)

Stop and uninstall the plugin

Stop the plugin:

  1. docker plugin disable sixsq/img-authz-plugin:<YOUR_CPU_ARCH>
  2. Remove the authorization-plugins attribute from /etc/docker/daemon.json
  3. kill -SIGHUP $(pidof dockerd)

Uninstall the plugin:

  1. docker plugin rm -f sixsq/img-authz-plugin:<YOUR_CPU_ARCH>

Developing, building and testing the plugin

Additional information for building and testing the plugin by yourself, can be found in the plugin’s GitHub repository here.

Credits: this plugin is an adaptation of the work done here: crosslibs/img-authz-plugin

Copyright 2020, SixSq