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Automatically Initialize RegistryOverrides with Image Content Type Policies

General

The HyperShift Operator (HO) will automatically initialize the control plane operator (CPO) with any image registry override information from any ImageContentSourcePolicy (ICSP) or any ImageDigestMirrorSet (IDMS) instances from an OpenShift management cluster.

!!! note

OpenShift management clusters do not allow both ICSP and IDMS CR instances.
IDMS CRs should be used with OpenShift release image versions 4.13 or higher.
ICSPs will be deprecated in future OpenShift release versions.

Technical Implementation Details

General

In hypershift-operator/main.go, the HO will look to see if its management cluster has either ICSP or IDMS capabilities. If so, it will retrieve the image registry information from the appropriate ICSP or IDMS instances and store them in a variable called imageRegistryOverrides. This variable is then provided to a custom release image provider called ProviderWithOpenShiftImageRegistryOverrides.

ProviderWithOpenShiftImageRegistryOverrides

The Lookup function for ProviderWithOpenShiftImageRegistryOverrides will use the source and mirror information in imageRegistryOverrides when attempting to look up release images. The ProviderWithOpenShiftImageRegistryOverrides is also provided to the HostedClusterReconciler as its ReleaseProvider. When the HostedClusterReconciler is reconciling, it will pass any image registry overrides to the ignition server reconciler and the CPO deployment specification.

Ignition Server

The ignition server reconciler forwards this information on to the ignition-server container as an environment variable called OPENSHIFT_IMG_OVERRIDES. hypershift/ignition-server/cmd/start.go retrieves this information for the ReleaseProvider for the TokenSecretReconciler. An important caveat for the ignition server, it cannot follow the ImageContentSourcePolicy or ImageDigestMirrorSet rules because there is not a runtime running inside the pod to do the transformations. So, it's necessary to do the image URL live translation to the custom registry address.

Control Plane Operator

The HostedClusterReconciler passes on the image registry override information as an environment variable in the CPO called OPENSHIFT_IMG_OVERRIDES. The CPO will check for the existence of this environment variable when it runs. If the variable exists, it's used to build the HostedControlPlaneReconciler's releaseProvider.