Enforcing the Use of Signed Images from Registry

For compliance and security reasons, system administrators often want to deploy software into a production system only when they are satisfied that:

  • the software comes from a trusted source
  • the software has not been modified since it was published, compromising its integrity

To meet these requirements, you can sign images stored in Oracle Cloud Infrastructure Registry. Signed images provide a way to verify both the source of an image and its integrity. Oracle Cloud Infrastructure Registry enables users or systems to push images to the registry and then sign them creating an image signature. An image signature associates an image with a master encryption key obtained from Oracle Cloud Infrastructure Vault.

Users or systems pulling a signed image from Oracle Cloud Infrastructure Registry can be confident both that the source of the image is trusted, and that the image's integrity has not been compromised. For more information, see Signing Images for Security.

To further enhance security, you can configure clusters you've created with Container Engine for Kubernetes to only allow the deployment of images from Oracle Cloud Infrastructure Registry that have been signed by particular master encryption keys. At a high level, these are the steps to follow:

  • Sign images in Oracle Cloud Infrastructure Registry with image signatures that use master encryption keys from Oracle Cloud Infrastructure Vault (see Signing Images for Security).
  • Create an image verification policy for a cluster that specifies which master encryption key(s) must have been used to sign images.
  • Enable the cluster to use the image verification policy to enforce the use of suitably signed images.

Note the following:

  • An image in Oracle Cloud Infrastructure Registry can be signed using multiple signatures, each associated with a different master encryption key. Provided a cluster's image verification policy includes at least one of the master encryption keys, the cluster allows the image to be pulled from Oracle Cloud Infrastructure Registry.
  • You can specify up to five master encryption keys in a cluster's image verification policy.
  • If you enable a cluster to use its image verification policy but do not specify the master encryption key(s) that must have been used to sign an image:
    • any signed image can be pulled from Oracle Cloud Infrastructure Registry, regardless of the master encryption keys used to sign it
    • any unsigned image can be pulled from Oracle Cloud Infrastructure Registry
  • If you enable a cluster to use its image verification policy but Container Engine for Kubernetes cannot connect to Oracle Cloud Infrastructure Registry, no images can be pulled from Oracle Cloud Infrastructure Registry.
  • Having enabled a cluster to use its image verification policy, you might later have an urgent requirement for a particular pod to pull an image that violates the policy. In this case, you can add the alpha.image-policy.k8s.io/break-glass: "true" annotation to the pod spec. Having added the annotation to the pod spec, the pod can pull any signed and unsigned images from Oracle Cloud Infrastructure Registry, regardless of the cluster's image verification policy.
  • A cluster enforces the use of images signed by master encryption keys included in its image verification policy, provided:
    • images are pulled from Oracle Cloud Infrastructure Registry (rather than from other registries)
    • images are signed using master encryption keys obtained from Oracle Cloud Infrastructure Vault

Required IAM Policies for Enforcing the Use of Signed Images

To enable clusters to include master encryption keys in image verification policies, you must give clusters permission to use keys from Oracle Cloud Infrastructure Vault. To grant this permission to all clusters in the tenancy:

Allow any-user to use keys in tenancy where request.user.id=<CLUSTER_OCID>

To enable clusters to pull signed images from Oracle Cloud Infrastructure Registry, you must give clusters permission to access repositories in Oracle Cloud Infrastructure Registry. To grant this permission to all clusters in the tenancy:

Allow any-user to read repos in tenancy where request.user.id=<CLUSTER_OCID>

For examples of how to create more granular policies, see Encrypting Kubernetes Secrets at Rest in Etcd.

Enforcing the Use of Signed Images

To enable a cluster to allow applications to pull only those images from Oracle Cloud Infrastructure Registry that have been signed using specific master encryption keys:

  1. If you don't already have access to an RSA asymmetric key in Oracle Cloud Infrastructure Vault, create one or more master encryption keys as RSA asymmetric keys. See To create a new master encryption key.
  2. Define an image verification policy for the cluster and specify at least one master encryption key that must have been used to sign images:
    1. In the Console, open the navigation menu and click Developer Services. Under Containers, click Kubernetes Clusters (OKE).
    2. Choose a Compartment you have permission to work in.
    3. On the Cluster List page, select the cluster for which you want to define an image verification policy.
    4. Under Resources, click Image Verification.
    5. Click Add Encryption Key.
    6. Select a master encryption key in Oracle Cloud Infrastructure Vault that must have been used to sign images.
    7. Click Add Key.

      If you want to allow images signed by different keys to be pulled, you can specify multiple master encryption keys.

    8. (Optional) Click Add Encryption Key and specify additional master encryption keys, if required.

      Note that if you do specify multiple master encryption keys, an image need only be signed by one of those keys. An image does not have to be signed by all of the master encryption keys you specify. You can specify up to five master encryption keys in the cluster's image verification policy.

  3. Select Enable image verification policies on this cluster to enable the cluster to use the image verification policy you've defined.

    From now on, the cluster allows applications to pull only those images from Oracle Cloud Infrastructure Registry that have been signed using master encryption keys included in the image verification policy. Attempts to pull disallowed images are recorded in application logs (see Viewing Application Logs on Worker Nodes).

  4. Sign the images that you want the cluster to allow, using image signatures that associate the images with one or more of the master encryption keys in the image verification policy you've defined. See Signing Images for Security.
  5. (optional) To deploy an application that pulls a signed image from Oracle Cloud Infrastructure Registry, follow the steps in Pulling Images from Registry during Deployment and specify the image in the application's manifest file.