Chapter 13. OCI Support and Red Hat Quay

Container registries such as Red Hat Quay were originally designed to support container images in the Docker image format. To promote the use of additional runtimes apart from Docker, the Open Container Initiative (OCI) was created to provide a standardization surrounding container runtimes and image formats. Most container registries support the OCI standardization as it is based on the Docker image manifest V2, Schema 2 format.

In addition to container images, a variety of artifacts have emerged that support not just individual applications, but the Kubernetes platform as a whole. These range from Open Policy Agent (OPA) policies for security and governance to Helm charts and Operators to aid in application deployment.

Red Hat Quay is a private container registry that not only stores container images, but supports an entire ecosystem of tooling to aid in the management of containers. Support for OCI based artifacts in 3 has extended from solely Helm to include cosign and ztsd compression schemes by default. As such, FEATURE_HELM_OCI_SUPPORT has been deprecated.

When Red Hat Quay 3 is deployed using the OpenShift Operator, support for Helm and OCI artifacts is now enabled by default under the FEATURE_GENERAL_OCI_SUPPORT configuration. If you need to explicitly enable the feature, for example, if it has previously been disabled or if you have upgraded from a version where it is not enabled by default, see the section Explicitly enabling OCI and Helm support.

13.1. Helm and OCI prerequisites

  • Trusted certificates: Communication between the Helm client and Quay is facilitated over HTTPS and as of Helm 3.5, support is only available for registries communicating over HTTPS with trusted certificates. In addition, the operating system must trust the certificates exposed by the registry. Support in future Helm releases will allow for communicating with remote registries insecurely. With that in mind, ensure that your operating system has been configured to trust the certificates used by Quay, for example:

    $ sudo cp rootCA.pem   /etc/pki/ca-trust/source/anchors/
    $ sudo update-ca-trust extract
  • Experimental feature: Many of the commands for interacting with Helm and OCI registries make use of the helm chart subcommand. At the time of writing, OCI support in Helm is still marked as an “experimental” feature and must be enabled explicitly. This is accomplished by setting the environment variable HELM_EXPERIMENTAL_OCI=1.
  • Install Helm client: Download your desired version from, for example, Unpack it and move the helm binary to its desired destination:

    $ tar -zxvf helm-v3.5.3-linux-amd64.tar.gz
    $ mv linux-amd64/helm /usr/local/bin/helm
  • Create organization in Quay: Create a new organization for storing the Helm charts, using the Quay registry UI. For example, create an organization named helm.

13.2. Using Helm charts with Quay

Helm, as a graduated project of the Cloud Native Computing Foundation (CNCF), has become the de facto package manager for Kubernetes as it simplifies how applications are packaged and deployed. Helm uses a packaging format called Charts which contain the Kubernetes resources representing an application. Charts can be made available for general distribution and consumption in repositories. A Helm repository is an HTTP server that serves an index.yaml metadata file and optionally a set of packaged charts. Beginning with Helm version 3, support was made available for distributing charts in OCI registries as an alternative to a traditional repository. To demonstrate how Quay can be used as a registry for Helm charts, an existing chart from a Helm repository will be used to showcase the interaction with OCI registries for chart developers and users.

In the following example, a sample etherpad chart is downloaded from from the Red Hat Community of Practice (CoP) repository and pushed to a local Red Hat Quay repository using the following steps:

  • Add the appropriate repository
  • Update the repository with the latest metadata
  • Download and untar the chart to create a local directory called etherpad

For example:

$ helm repo add redhat-cop
$ helm repo update
$ helm pull redhat-cop/etherpad --version=0.0.4 --untar

Tagging the chart requires use of the helm chart save command - this corresponds to using podman tag for tagging images.

$ helm chart save ./etherpad

digest:  6850d9b21dd4b87cf20ad49f2e2c7def9655c52ea573e1ddb9d1464eeb6a46a6
size:    3.5 KiB
name:    etherpad
version: 0.0.4
0.0.4: saved

Use the helm chart list command to see the local instance of the chart:

helm chart list

REF                                                                               NAME     VERSION DIGEST SIZE   CREATED etherpad 0.0.4   ce0233f 3.5 KiB 23 seconds

Before pushing the chart, log in to the repository using the helm registry login command:

$ helm registry login
Username: quayadmin
Login succeeded

Push the chart to your local Quay repository using the helm chart push command:

$ helm chart push

The push refers to repository []
digest:  ce0233fd014992b8e27cc648cdabbebd4dd6850aca8fb8e50f7eef6f2f49833d
size:    3.5 KiB
name:    etherpad
version: 0.0.4
0.0.4: pushed to remote (1 layer, 3.5 KiB total)

To test that the push worked, delete the local copy and then pull the chart from the repository:

$ helm chart rm
$ rm -rf etherpad
$ helm chart pull

0.0.4: Pulling from
digest:  6850d9b21dd4b87cf20ad49f2e2c7def9655c52ea573e1ddb9d1464eeb6a46a6
size:    3.5 KiB
name:    etherpad
version: 0.0.4
Status: Downloaded newer chart for

Use the helm chart export command to extract the chart files:

$ helm chart export

digest:  ce0233fd014992b8e27cc648cdabbebd4dd6850aca8fb8e50f7eef6f2f49833d
size:    3.5 KiB
name:    etherpad
version: 0.0.4
Exported chart to etherpad/

13.3. OCI and Helm configuration

Support for Helm is now supported under the FEATURE_GENERAL_OCI_SUPPORT property. If you need to explicitly enable the feature, for example, if it has previously been disabled or if you have upgraded from a version where it is not enabled by default, you need to add two properties in the Quay configuration to enable the use of OCI artifacts:


Table 13.1. OCI and Helm configuration




Enable support for OCI artifacts

Default: True



Enable support for Helm artifacts

Default: True


As of Red Hat Quay 3, FEATURE_HELM_OCI_SUPPORT has been deprecated and will be removed in a future version of Red Hat Quay. In Red Hat Quay 3, Helm artifacts are supported by default and included under the FEATURE_GENERAL_OCI_SUPPORT property. Users are no longer required to update their config.yaml files to enable support.

13.4. Cosign OCI support with Red Hat Quay

Cosign is a tool that can be used to sign and verify container images. It uses the ECDSA-P256 signature algorithm and Red Hat’s Simple Signing payload format to create public keys that are stored in PKIX files. Private keys are stored as encrypted PEM files.

Cosign currently supports the following:

  • Hardware and KMS Signing
  • Bring-your-own PKI
  • Built-in binary transparency and timestamping service

13.5. Using cosign with quay

If you have Go 1.16+, you can directly install cosign with the following command:

$ go install
go: downloading v1.0.0
go: downloading v3.1.0

Next, generate a keypair:

$ cosign generate-key-pair
Enter password for private key:
Enter again:
Private key written to cosign.key
Public key written to

Sign the keypair with the following command:

$ cosign sign -key cosign.key
Enter password for private key:
Pushing signature to:

Some users may experience the following error:

error: signing getting remote image: GET UNAUTHORIZED: access to the requested resource is not authorized; map[]

Because cosign relies on ~/.docker/config.json for authorization, you might need to execute the following command:

$ podman login --authfile ~/.docker/config.json
Login Succeeded!

You can see the updated authorization configuration using the following command:

$ cat ~/.docker/config.json
	"auths": {
		"": {
			"auth": "cXVheWFkbWluOnBhc3N3b3Jk"

13.6. Adding other OCI media types to Quay

Helm, cosign, and ztsd compression scheme artifacts are built into Red Hat Quay 3 by default. For any other OCI media type that is not supported by default, you can add them to the ALLOWED_OCI_ARTIFACT_TYPES configuration in Quay’s config.yaml using the following format:

  <oci config type 1>:
  - <oci layer type 1>
  - <oci layer type 2>

  <oci config type 2>:
  - <oci layer type 3>
  - <oci layer type 4>

For example, you can add Singularity (SIF) support by adding the following to your config.yaml:

  - application/
  - application/tar+gzip
  - application/vnd.sylabs.sif.layer.v1+tar

When adding OCI media types that are not configured by default, users will also need to manually add support for cosign and Helm if desired. The ztsd compression scheme is supported by default, so users will not need to add that OCI media type to their config.yaml to enable support.

13.7. Disabling OCI artifacts in Quay

If you want to disable OCI artifact support, you can set FEATURE_GENERAL_OCI_SUPPORT to False in your config.yaml: