Automation with content trust
Estimated reading time: 3 minutes
It is very common for Docker Content Trust to be built into existing automation systems. To allow tools to wrap Docker and push trusted content, there are environment variables that can be passed through to the client.
This guide follows the steps as described here so please read that and understand its prerequisites.
When working directly with the Notary client, it uses its own set of environment variables.
Add a delegation private key
To automate importing a delegation private key to the local Docker trust store, we need to pass a passphrase for the new key. This passphrase will be required everytime that delegation signs a tag.
$ export DOCKER_CONTENT_TRUST_REPOSITORY_PASSPHRASE="mypassphrase123" $ docker trust key load delegation.key --name jeff Loading key from "delegation.key"... Successfully imported key from delegation.key
Add a delegation public key
If you initialising a repository at the same time as adding a Delegation public key, then you will need to use the local Notary Canonical Root Key’s passphrase to create the repositories trust data. If the repository has already been initiated then you only need the repositories passphrase.
# Export the Local Root Key Passphrase if required. $ export DOCKER_CONTENT_TRUST_ROOT_PASSPHRASE="rootpassphrase123" # Export the Repository Passphrase $ export DOCKER_CONTENT_TRUST_REPOSITORY_PASSPHRASE="repopassphrase123" # Initialise Repo and Push Delegation $ docker trust signer add --key delegation.crt jeff registry.example.com/admin/demo Adding signer "jeff" to registry.example.com/admin/demo... Initializing signed repository for registry.example.com/admin/demo... Successfully initialized "registry.example.com/admin/demo" Successfully added signer: registry.example.com/admin/demo
Sign an image
Finally when signing an image, we will need to export the passphrase of the
signing key. This was created when the key was loaded into the local Docker
trust store with
$ docker trust key load.
$ export DOCKER_CONTENT_TRUST_REPOSITORY_PASSPHRASE="mypassphrase123" $ docker trust sign registry.example.com/admin/demo:1 Signing and pushing trust data for local image registry.example.com/admin/demo:1, may overwrite remote trust data The push refers to repository [registry.example.com/admin/demo] 428c97da766c: Layer already exists 2: digest: sha256:1a6fd470b9ce10849be79e99529a88371dff60c60aab424c077007f6979b4812 size: 524 Signing and pushing trust metadata Successfully signed registry.example.com/admin/demo:1
Build with content trust
You can also build with content trust. Before running the
docker build command,
you should set the environment variable
DOCKER_CONTENT_TRUST either manually or
in a scripted fashion. Consider the simple Dockerfile below.
# syntax=docker/dockerfile:1 FROM docker/trusttest:latest RUN echo
FROM tag is pulling a signed image. You cannot build an image that has a
FROM that is not either present locally or signed. Given that content trust
data exists for the tag
latest, the following build should succeed:
$ docker build -t docker/trusttest:testing . Using default tag: latest latest: Pulling from docker/trusttest b3dbab3810fc: Pull complete a9539b34a6ab: Pull complete Digest: sha256:d149ab53f871
If content trust is enabled, building from a Dockerfile that relies on tag without trust data, causes the build command to fail:
$ docker build -t docker/trusttest:testing . unable to process Dockerfile: No trust data for notrust
- Delegations for content trust
- Content trust in Docker
- Manage keys for content trust
- Play in a content trust sandbox