Image configuration resources | Images | OpenShift Container Platform 4.7

Image controller configuration parameters
Configuring image registry settings

Use the following procedure to configure image registries.

Image controller configuration parameters

The image.config.openshift.io/cluster resource holds cluster-wide information about how to handle images. The canonical, and only valid name is cluster. Its spec offers the following configuration parameters.

Parameters such as DisableScheduledImport, MaxImagesBulkImportedPerRepository, MaxScheduledImportsPerMinute, ScheduledImageImportMinimumIntervalSeconds, InternalRegistryHostname are not configurable.

Parameter Description

Parameter	Description
`allowedRegistriesForImport`	Limits the container image registries from which normal users can import images. Set this list to the registries that you trust to contain valid images, and that you want applications to be able to import from. Users with permission to create images or `ImageStreamMappings` from the API are not affected by this policy. Typically only cluster administrators have the appropriate permissions. Every element of this list contains a location of the registry specified by the registry domain name. `domainName`: Specifies a domain name for the registry. In case the registry uses a non-standard `80` or `443` port, the port should be included in the domain name as well. `insecure`: Insecure indicates whether the registry is secure or insecure. By default, if not otherwise specified, the registry is assumed to be secure.
`additionalTrustedCA`	A reference to a config map containing additional CAs that should be trusted during `image stream import`, `pod image pull`, `openshift-image-registry pullthrough`, and builds. The namespace for this config map is `openshift-config`. The format of the config map is to use the registry hostname as the key, and the PEM-encoded certificate as the value, for each additional registry CA to trust.
`externalRegistryHostnames`	Provides the hostnames for the default external image registry. The external hostname should be set only when the image registry is exposed externally. The first value is used in `publicDockerImageRepository` field in image streams. The value must be in `hostname[:port]` format.
`registrySources`	Contains configuration that determines how the container runtime should treat individual registries when accessing images for builds and pods. For instance, whether or not to allow insecure access. It does not contain configuration for the internal cluster registry. `insecureRegistries`: Registries which do not have a valid TLS certificate or only support HTTP connections. `blockedRegistries`: Registries for which image pull and push actions are denied. All other registries are allowed. `allowedRegistries`: Registries for which image pull and push actions are allowed. All other registries are blocked. `containerRuntimeSearchRegistries`: Registries for which image pull and push actions are allowed using image short names. All other registries are blocked. Either `blockedRegistries` or `allowedRegistries` can be set, but not both.

allowedRegistriesForImport

Limits the container image registries from which normal users can import images. Set this list to the registries that you trust to contain valid images, and that you want applications to be able to import from. Users with permission to create images or ImageStreamMappings from the API are not affected by this policy. Typically only cluster administrators have the appropriate permissions.

Every element of this list contains a location of the registry specified by the registry domain name.

domainName: Specifies a domain name for the registry. In case the registry uses a non-standard 80 or 443 port, the port should be included in the domain name as well.

insecure: Insecure indicates whether the registry is secure or insecure. By default, if not otherwise specified, the registry is assumed to be secure.

additionalTrustedCA

A reference to a config map containing additional CAs that should be trusted during image stream import, pod image pull, openshift-image-registry pullthrough, and builds.

The namespace for this config map is openshift-config. The format of the config map is to use the registry hostname as the key, and the PEM-encoded certificate as the value, for each additional registry CA to trust.

externalRegistryHostnames

Provides the hostnames for the default external image registry. The external hostname should be set only when the image registry is exposed externally. The first value is used in publicDockerImageRepository field in image streams. The value must be in hostname[:port] format.

registrySources

Contains configuration that determines how the container runtime should treat individual registries when accessing images for builds and pods. For instance, whether or not to allow insecure access. It does not contain configuration for the internal cluster registry.

insecureRegistries: Registries which do not have a valid TLS certificate or only support HTTP connections.

blockedRegistries: Registries for which image pull and push actions are denied. All other registries are allowed.

allowedRegistries: Registries for which image pull and push actions are allowed. All other registries are blocked.

containerRuntimeSearchRegistries: Registries for which image pull and push actions are allowed using image short names. All other registries are blocked.

Either blockedRegistries or allowedRegistries can be set, but not both.

When the allowedRegistries parameter is defined, all registries, including registry.redhat.io and quay.io registries and the default internal image registry, are blocked unless explicitly listed. When using the parameter, to prevent pod failure, add all registries including the registry.redhat.io and quay.io registries and the internalRegistryHostname to the allowedRegistries list, as they are required by payload images within your environment. For disconnected clusters, mirror registries should also be added.

The status field of the image.config.openshift.io/cluster resource holds observed values from the cluster.

Parameter Description

Parameter	Description
`internalRegistryHostname`	Set by the Image Registry Operator, which controls the `internalRegistryHostname`. It sets the hostname for the default internal image registry. The value must be in `hostname[:port]` format. For backward compatibility, you can still use the `OPENSHIFT_DEFAULT_REGISTRY` environment variable, but this setting overrides the environment variable.
`externalRegistryHostnames`	Set by the Image Registry Operator, provides the external hostnames for the image registry when it is exposed externally. The first value is used in `publicDockerImageRepository` field in image streams. The values must be in `hostname[:port]` format.

internalRegistryHostname

Set by the Image Registry Operator, which controls the internalRegistryHostname. It sets the hostname for the default internal image registry. The value must be in hostname[:port] format. For backward compatibility, you can still use the OPENSHIFT_DEFAULT_REGISTRY environment variable, but this setting overrides the environment variable.

externalRegistryHostnames

Set by the Image Registry Operator, provides the external hostnames for the image registry when it is exposed externally. The first value is used in publicDockerImageRepository field in image streams. The values must be in hostname[:port] format.

Configuring image registry settings

You can configure image registry settings by editing the image.config.openshift.io/cluster custom resource (CR). The Machine Config Operator (MCO) watches the image.config.openshift.io/cluster CR for any changes to the registries and reboots the nodes when it detects changes.

Procedure

Edit the image.config.openshift.io/cluster custom resource:

$ oc edit image.config.openshift.io/cluster

The following is an example image.config.openshift.io/cluster CR:

apiVersion: config.openshift.io/v1
kind: Image (1)
metadata:
  annotations:
    release.openshift.io/create-only: "true"
  creationTimestamp: "2019-05-17T13:44:26Z"
  generation: 1
  name: cluster
  resourceVersion: "8302"
  selfLink: /apis/config.openshift.io/v1/images/cluster
  uid: e34555da-78a9-11e9-b92b-06d6c7da38dc
spec:
  allowedRegistriesForImport: (2)
    - domainName: quay.io
      insecure: false
  additionalTrustedCA: (3)
    name: myconfigmap
  registrySources: (4)
    allowedRegistries:
    - example.com
    - quay.io
    - registry.redhat.io
    - image-registry.openshift-image-registry.svc:5000
    insecureRegistries:
    - insecure.com
status:
  internalRegistryHostname: image-registry.openshift-image-registry.svc:5000

1	`Image`: Holds cluster-wide information about how to handle images. The canonical, and only valid name is `cluster`.
2	`allowedRegistriesForImport`: Limits the container image registries from which normal users may import images. Set this list to the registries that you trust to contain valid images, and that you want applications to be able to import from. Users with permission to create images or `ImageStreamMappings` from the API are not affected by this policy. Typically only cluster administrators have the appropriate permissions.
3	`additionalTrustedCA`: A reference to a config map containing additional certificate authorities (CA) that are trusted during image stream import, pod image pull, `openshift-image-registry` pullthrough, and builds. The namespace for this config map is `openshift-config`. The format of the config map is to use the registry hostname as the key, and the PEM certificate as the value, for each additional registry CA to trust.
4	`registrySources`: Contains configuration that determines whether the container runtime allows or blocks individual registries when accessing images for builds and pods. Either the `allowedRegistries` parameter or the `blockedRegistries` parameter can be set, but not both. You can also define whether or not to allow access to insecure registries or registries that allow registries that use image short names. This example uses the `allowedRegistries` parameter, which defines the registries that are allowed to be used. The insecure registry `insecure.com` is also allowed. The `registrySources` paramter does not contain configuration for the internal cluster registry.

When the allowedRegistries parameter is defined, all registries, including the registry.redhat.io and quay.io registries and the default internal image registry, are blocked unless explicitly listed. If you use the parameter, to prevent pod failure, you must add the registry.redhat.io and quay.io registries and the internalRegistryHostname to the allowedRegistries list, because they are required by payload images within your environment. Do not add the registry.redhat.io and quay.io registries to the blockedRegistries list.

Insecure external registries should be avoided to reduce possible security risks.

To check that the changes are applied, list your nodes:

$ oc get nodes

Example output

NAME                                       STATUS                     ROLES    AGE   VERSION
ci-ln-j5cd0qt-f76d1-vfj5x-master-0         Ready                         master   98m   v1.19.0+7070803
ci-ln-j5cd0qt-f76d1-vfj5x-master-1         Ready,SchedulingDisabled      master   99m   v1.19.0+7070803
ci-ln-j5cd0qt-f76d1-vfj5x-master-2         Ready                         master   98m   v1.19.0+7070803
ci-ln-j5cd0qt-f76d1-vfj5x-worker-b-nsnd4   Ready                         worker   90m   v1.19.0+7070803
ci-ln-j5cd0qt-f76d1-vfj5x-worker-c-5z2gz   NotReady,SchedulingDisabled   worker   90m   v1.19.0+7070803
ci-ln-j5cd0qt-f76d1-vfj5x-worker-d-stsjv   Ready                         worker   90m   v1.19.0+7070803

Adding specific registries

You can add a list of registries that are permitted for image pull and push actions by editing the image.config.openshift.io/cluster custom resource (CR). OpenShift Container Platform applies the changes to this CR to all nodes in the cluster.

When pulling or pushing images, the container runtime searches the registries listed under the registrySources parameter in the image.config.openshift.io/cluster CR. If you created a list of registries under the allowedRegistries parameter, the container runtime searches only those registries. Registries not in the list are blocked.

When the allowedRegistries parameter is defined, all registries, including the registry.redhat.io and quay.io registries and the default internal image registry, are blocked unless explicitly listed. If you use the parameter, to prevent pod failure, add the registry.redhat.io and quay.io registries and the internalRegistryHostname to the allowedRegistries list, as they are required by payload images within your environment. For disconnected clusters, mirror registries should also be added.

Procedure

Edit the image.config.openshift.io/cluster CR:

$ oc edit image.config.openshift.io/cluster

The following is an example image.config.openshift.io/cluster CR with an allowed list:

apiVersion: config.openshift.io/v1
kind: Image
metadata:
  annotations:
    release.openshift.io/create-only: "true"
  creationTimestamp: "2019-05-17T13:44:26Z"
  generation: 1
  name: cluster
  resourceVersion: "8302"
  selfLink: /apis/config.openshift.io/v1/images/cluster
  uid: e34555da-78a9-11e9-b92b-06d6c7da38dc
spec:
  registrySources: (1)
    allowedRegistries: (2)
    - example.com
    - quay.io
    - registry.redhat.io
    - reg1.io
    - image-registry.openshift-image-registry.svc:5000
status:
  internalRegistryHostname: image-registry.openshift-image-registry.svc:5000

1	`registrySources`: Contains configurations that determine how the container runtime should treat individual registries when accessing images for builds and pods. It does not contain configuration for the internal cluster registry.
2	`allowedRegistries`: Registries to use for image pull and push actions. All other registries are blocked.

Either the allowedRegistries parameter or the blockedRegistries parameter can be set, but not both.

To check that the registries have been added to the policy file, use the following command on a node:

$ cat /host/etc/containers/policy.json

The following policy indicates that only images from the example.com, quay.io, and registry.redhat.io registries are permitted for image pulls and pushes:

Example image signature policy file

{
   "default":[
      {
         "type":"reject"
      }
   ],
   "transports":{
      "atomic":{
         "example.com":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "image-registry.openshift-image-registry.svc:5000":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "insecure.com":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "quay.io":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "reg4.io/myrepo/myapp:latest":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "registry.redhat.io":[
            {
               "type":"insecureAcceptAnything"
            }
         ]
      },
      "docker":{
         "example.com":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "image-registry.openshift-image-registry.svc:5000":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "insecure.com":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "quay.io":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "reg4.io/myrepo/myapp:latest":[
            {
               "type":"insecureAcceptAnything"
            }
         ],
         "registry.redhat.io":[
            {
               "type":"insecureAcceptAnything"
            }
         ]
      },
      "docker-daemon":{
         "":[
            {
               "type":"insecureAcceptAnything"
            }
         ]
      }
   }
}

If your cluster uses the registrySources.insecureRegistries parameter, ensure that any insecure registries are included in the allowed list.

For example:

spec:
  registrySources:
    insecureRegistries:
    - insecure.com
    allowedRegistries:
    - example.com
    - quay.io
    - registry.redhat.io
    - insecure.com
    - image-registry.openshift-image-registry.svc:5000

Blocking specific registries

You can block any registry by editing the image.config.openshift.io/cluster custom resource (CR). OpenShift Container Platform applies the changes to this CR to all nodes in the cluster.

When pulling or pushing images, the container runtime searches the registries listed under the registrySources parameter in the image.config.openshift.io/cluster CR. If you created a list of registries under the blockedRegistries parameter, the container runtime does not search those registries. All other registries are allowed.

To prevent pod failure, do not add the registry.redhat.io and quay.io registries to the blockedRegistries list, as they are required by payload images within your environment.

Procedure

Edit the image.config.openshift.io/cluster CR:

$ oc edit image.config.openshift.io/cluster

The following is an example image.config.openshift.io/cluster CR with a blocked list:

apiVersion: config.openshift.io/v1
kind: Image
metadata:
  annotations:
    release.openshift.io/create-only: "true"
  creationTimestamp: "2019-05-17T13:44:26Z"
  generation: 1
  name: cluster
  resourceVersion: "8302"
  selfLink: /apis/config.openshift.io/v1/images/cluster
  uid: e34555da-78a9-11e9-b92b-06d6c7da38dc
spec:
  registrySources: (1)
    blockedRegistries: (2)
    - untrusted.com
status:
  internalRegistryHostname: image-registry.openshift-image-registry.svc:5000

1	`registrySources`: Contains configurations that determine how the container runtime should treat individual registries when accessing images for builds and pods. It does not contain configuration for the internal cluster registry.
2	Specify registries that should not be used for image pull and push actions. All other registries are allowed.

Either the blockedRegistries registry or the allowedRegistries registry can be set, but not both.

To check that the registries have been added to the policy file, use the following command on a node:
```
$ cat /host/etc/containers/registries.conf
```
The following example indicates that images from the untrusted.com registry are prevented for image pulls and pushes:
Example output
```
unqualified-search-registries = ["registry.access.redhat.com", "docker.io"]

[[registry]]
  prefix = ""
  location = "untrusted.com"
  blocked = true
```

Allowing insecure registries

You can add insecure registries by editing the image.config.openshift.io/cluster custom resource (CR). OpenShift Container Platform applies the changes to this CR to all nodes in the cluster.

Registries that do not use valid SSL certificates or do not require HTTPS connections are considered insecure.

Insecure external registries should be avoided to reduce possible security risks.

Procedure

Edit the image.config.openshift.io/cluster CR:

$ oc edit image.config.openshift.io/cluster

The following is an example image.config.openshift.io/cluster CR with an insecure registries list:

apiVersion: config.openshift.io/v1
kind: Image
metadata:
  annotations:
    release.openshift.io/create-only: "true"
  creationTimestamp: "2019-05-17T13:44:26Z"
  generation: 1
  name: cluster
  resourceVersion: "8302"
  selfLink: /apis/config.openshift.io/v1/images/cluster
  uid: e34555da-78a9-11e9-b92b-06d6c7da38dc
spec:
  registrySources: (1)
    insecureRegistries: (2)
    - insecure.com
    allowedRegistries:
    - example.com
    - quay.io
    - registry.redhat.io
    - insecure.com (3)
    - reg4.io
    - image-registry.openshift-image-registry.svc:5000
status:
  internalRegistryHostname: image-registry.openshift-image-registry.svc:5000

1	`registrySources`: Contains configurations that determine how the container runtime should treat individual registries when accessing images for builds and pods. It does not contain configuration for the internal cluster registry.
2	Specify an insecure registry.
3	Ensure that any insecure registries are included in the allowedRegistries list.

When the allowedRegistries parameter is defined, all registries, including the registry.redhat.io and quay.io registries and the default internal image registry, are blocked unless explicitly listed. If you use the parameter, to prevent pod failure, add all registries including the registry.redhat.io and quay.io registries and the internalRegistryHostname to the allowedRegistries list, as they are required by payload images within your environment. For disconnected clusters, mirror registries should also be added.

The Machine Config Operator (MCO) watches the image.config.openshift.io/cluster CR for any changes to the registries, then drains and uncordons the nodes when it detects changes. After the nodes return to the Ready state, changes to the insecure and blocked registries appear in the /etc/containers/registries.conf file on each node.

To check that the registries have been added to the policy file, use the following command on a node:
```
$ cat /host/etc/containers/registries.conf
```
The following example indicates that images from the insecure.com registry is insecure and is allowed for image pulls and pushes.
Example output
```
unqualified-search-registries = ["registry.access.redhat.com", "docker.io"]

[[registry]]
  prefix = ""
  location = "insecure.com"
  insecure = true
```

Adding registries that allow image short names

You can add registries to search for an image short name by editing the image.config.openshift.io/cluster custom resource (CR). OpenShift Container Platform applies the changes to this CR to all nodes in the cluster.

An image short name enables you to search for images without including the fully qualified domain name in the pull spec. For example, you could use rhel7/etcd instead of registry.access.redhat.com/rhe7/etcd.

You might use short names in situations where using the full path is not practical. For example, if your cluster references multiple internal registries whose DNS changes frequently, you would need to update the fully qualified domain names in your pull specs with each change. In this case, using an image short name might be beneficial.

When pulling or pushing images, the container runtime searches the registries listed under the registrySources parameter in the image.config.openshift.io/cluster CR. If you created a list of registries under the containerRuntimeSearchRegistries parameter, when pulling an image with a short name, the container runtime searches those registries.

Using image short names with public registries is strongly discouraged. You should use image short names with only internal or private registries.

If you list public registries under the containerRuntimeSearchRegistries parameter, you expose your credentials to all the registries on the list and you risk network and registry attacks. You should always use fully-qualified image names with public registries.

The Machine Config Operator (MCO) watches the image.config.openshift.io/cluster resource for any changes to the registries. When the MCO detects a change, it drains the nodes, applies the change, and uncordons the nodes. After the nodes return to the Ready state, if the containerRuntimeSearchRegistries parameter is added, the MCO creates a file in the /etc/containers/registries.conf.d directory on each node with the listed registries. The file overrides the default list of unqualified search registries in the /host/etc/containers/registries.conf file. There is no way to fall back to the default list of unqualified search registries.

The containerRuntimeSearchRegistries parameter works only with the Podman and CRI-O container engines. The registries in the list can be used only in pod specs, not in builds and image streams.

Procedure

Edit the image.config.openshift.io/cluster custom resource:

$ oc edit image.config.openshift.io/cluster

The following is an example image.config.openshift.io/cluster CR:

apiVersion: config.openshift.io/v1
kind: Image
metadata:
  annotations:
    release.openshift.io/create-only: "true"
  creationTimestamp: "2019-05-17T13:44:26Z"
  generation: 1
  name: cluster
  resourceVersion: "8302"
  selfLink: /apis/config.openshift.io/v1/images/cluster
  uid: e34555da-78a9-11e9-b92b-06d6c7da38dc
spec:
  allowedRegistriesForImport:
    - domainName: quay.io
      insecure: false
  additionalTrustedCA:
    name: myconfigmap
  registrySources:
    containerRuntimeSearchRegistries: (1)
    - reg1.io
    - reg2.io
    - reg3.io
    allowedRegistries: (2)
    - example.com
    - quay.io
    - registry.redhat.io
    - reg1.io
    - reg2.io
    - reg3.io
    - image-registry.openshift-image-registry.svc:5000
...
status:
  internalRegistryHostname: image-registry.openshift-image-registry.svc:5000

1	Specify registries to use with image short names. You should use image short names with only internal or private registries to reduce possible security risks.
2	Ensure that any registries listed under `containerRuntimeSearchRegistries` are included in the `allowedRegistries` list.

When the allowedRegistries parameter is defined, all registries, including the registry.redhat.io and quay.io registries and the default internal image registry, are blocked unless explicitly listed. If you use this parameter, to prevent pod failure, add all registries including the registry.redhat.io and quay.io registries and the internalRegistryHostname to the allowedRegistries list, as they are required by payload images within your environment. For disconnected clusters, mirror registries should also be added.

To check that the registries have been added, when a node returns to the Ready state, use the following command on the node:

$ cat /host/etc/containers/registries.conf.d/01-image-searchRegistries.conf

Example output

unqualified-search-registries = ['reg1.io', 'reg2.io', 'reg3.io']

Configuring additional trust stores for image registry access

The image.config.openshift.io/cluster custom resource can contain a reference to a config map that contains additional certificate authorities to be trusted during image registry access.

Prerequisites

The certificate authorities (CA) must be PEM-encoded.

Procedure

You can create a config map in the openshift-config namespace and use its name in AdditionalTrustedCA in the image.config.openshift.io custom resource to provide additional CAs that should be trusted when contacting external registries.

The config map key is the hostname of a registry with the port for which this CA is to be trusted, and the base64-encoded certificate is the value, for each additional registry CA to trust.

Image registry CA config map example

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-registry-ca
data:
  registry.example.com: |
    -----BEGIN certificate-----
    ...
    -----END certificate-----
  registry-with-port.example.com..5000: | (1)
    -----BEGIN certificate-----
    ...
    -----END certificate-----

1	If the registry has the port, such as `registry-with-port.example.com:5000`, `:` should be replaced with `..`.

You can configure additional CAs with the following procedure.

To configure an additional CA:

$ oc create configmap registry-config --from-file=<external_registry_address>=ca.crt -n openshift-config

$ oc edit image.config.openshift.io cluster

spec:
  additionalTrustedCA:
    name: registry-config

Configuring image registry repository mirroring

Setting up container registry repository mirroring enables you to do the following:

Configure your OpenShift Container Platform cluster to redirect requests to pull images from a repository on a source image registry and have it resolved by a repository on a mirrored image registry.
Identify multiple mirrored repositories for each target repository, to make sure that if one mirror is down, another can be used.

The attributes of repository mirroring in OpenShift Container Platform include:

Image pulls are resilient to registry downtimes.
Clusters in restricted networks can pull images from critical locations, such as quay.io, and have registries behind a company firewall provide the requested images.
A particular order of registries is tried when an image pull request is made, with the permanent registry typically being the last one tried.
The mirror information you enter is added to the /etc/containers/registries.conf file on every node in the OpenShift Container Platform cluster.
When a node makes a request for an image from the source repository, it tries each mirrored repository in turn until it finds the requested content. If all mirrors fail, the cluster tries the source repository. If successful, the image is pulled to the node.

Setting up repository mirroring can be done in the following ways:

At OpenShift Container Platform installation:

By pulling container images needed by OpenShift Container Platform and then bringing those images behind your company’s firewall, you can install OpenShift Container Platform into a datacenter that is in a restricted network.
After OpenShift Container Platform installation:

Even if you don’t configure mirroring during OpenShift Container Platform installation, you can do so later using the ImageContentSourcePolicy object.

The following procedure provides a post-installation mirror configuration, where you create an ImageContentSourcePolicy object that identifies:

The source of the container image repository you want to mirror.
A separate entry for each mirror repository you want to offer the content requested from the source repository.

You can only configure global pull secrets for clusters that have an ImageContentSourcePolicy object. You cannot add a pull secret to a project.

Prerequisites

Access to the cluster as a user with the cluster-admin role.

Procedure

Configure mirrored repositories, by either:
- Setting up a mirrored repository with Red Hat Quay, as described in Red Hat Quay Repository Mirroring. Using Red Hat Quay allows you to copy images from one repository to another and also automatically sync those repositories repeatedly over time.
- Using a tool such as skopeo to copy images manually from the source directory to the mirrored repository.
  
  For example, after installing the skopeo RPM package on a Red Hat Enterprise Linux (RHEL) 7 or RHEL 8 system, use the skopeo command as shown in this example:
  $ skopeo copy \ docker://registry.access.redhat.com/ubi8/ubi-minimal@sha256:5cfbaf45ca96806917830c183e9f37df2e913b187adb32e89fd83fa455ebaa6 \ docker://example.io/example/ubi-minimal
  In this example, you have a container image registry that is named example.io with an image repository named example to which you want to copy the ubi8/ubi-minimal image from registry.access.redhat.com. After you create the registry, you can configure your OpenShift Container Platform cluster to redirect requests made of the source repository to the mirrored repository.
Log in to your OpenShift Container Platform cluster.

Create an ImageContentSourcePolicy file (for example, registryrepomirror.yaml), replacing the source and mirrors with your own registry and repository pairs and images:

apiVersion: operator.openshift.io/v1alpha1
kind: ImageContentSourcePolicy
metadata:
  name: ubi8repo
spec:
  repositoryDigestMirrors:
  - mirrors:
    - example.io/example/ubi-minimal (1)
    source: registry.access.redhat.com/ubi8/ubi-minimal (2)
  - mirrors:
    - example.com/example/ubi-minimal
    source: registry.access.redhat.com/ubi8/ubi-minimal
  - mirrors:
    - mirror.example.com/redhat
    source: registry.redhat.io/openshift4 (3)

1	Indicates the name of the image registry and repository.
2	Indicates the registry and repository containing the content that is mirrored.
3	You can configure a namespace inside a registry to use any image in that namespace. If you use a registry domain as a source, the `ImageContentSourcePolicy` resource is applied to all repositories from the registry.

Create the new ImageContentSourcePolicy object:
```
$ oc create -f registryrepomirror.yaml
```
After the ImageContentSourcePolicy object is created, the new settings are deployed to each node and the cluster starts using the mirrored repository for requests to the source repository.

To check that the mirrored configuration settings, are applied, do the following on one of the nodes.

List your nodes:

$ oc get node

Example output

NAME                           STATUS                     ROLES    AGE  VERSION
ip-10-0-137-44.ec2.internal    Ready                      worker   7m   v1.20.0
ip-10-0-138-148.ec2.internal   Ready                      master   11m  v1.20.0
ip-10-0-139-122.ec2.internal   Ready                      master   11m  v1.20.0
ip-10-0-147-35.ec2.internal    Ready,SchedulingDisabled   worker   7m   v1.20.0
ip-10-0-153-12.ec2.internal    Ready                      worker   7m   v1.20.0
ip-10-0-154-10.ec2.internal    Ready                      master   11m  v1.20.0

You can see that scheduling on each worker node is disabled as the change is being applied.

Start the debugging process to access the node:

$ oc debug node/ip-10-0-147-35.ec2.internal

Example output

Starting pod/ip-10-0-147-35ec2internal-debug ...
To use host binaries, run `chroot /host`

Access the node’s files:
```
sh-4.2# chroot /host
```

Check the /etc/containers/registries.conf file to make sure the changes were made:

sh-4.2# cat /etc/containers/registries.conf

Example output

unqualified-search-registries = ["registry.access.redhat.com", "docker.io"]
[[registry]]
  location = "registry.access.redhat.com/ubi8/"
  insecure = false
  blocked = false
  mirror-by-digest-only = true
  prefix = ""

  [[registry.mirror]]
    location = "example.io/example/ubi8-minimal"
    insecure = false

  [[registry.mirror]]
    location = "example.com/example/ubi8-minimal"
    insecure = false

Pull an image digest to the node from the source and check if it is resolved by the mirror. ImageContentSourcePolicy objects support image digests only, not image tags.
```
sh-4.2# podman pull --log-level=debug registry.access.redhat.com/ubi8/ubi-minimal@sha256:5cfbaf45ca96806917830c183e9f37df2e913b187adb32e89fd83fa455ebaa6
```

Troubleshooting repository mirroring

If the repository mirroring procedure does not work as described, use the following information about how repository mirroring works to help troubleshoot the problem.

The first working mirror is used to supply the pulled image.
The main registry is only used if no other mirror works.
From the system context, the Insecure flags are used as fallback.
The format of the /etc/containers/registries.conf file has changed recently. It is now version 2 and in TOML format.

Additional resources

For more information about global pull secrets, see Updating the global cluster pull secret.