Minishift and the Enterprise: Disconnected Image Registry

Posted: May 31st, 2018 | Author: | Filed under: Technology | Tags: , , , | No Comments »

Security continues to be a priority in most organizations. Any breach may result in intellectual or financial losses. Reducing access to external systems by internal resources is one was to limit the threat potential. One such method is to place a middleman, or proxy, between internal and external resources to govern the types of traffic. Considerations for how the Container Development Kit (CDK) can traverse proxy servers were covered in a prior blog. However, many organizations are further reducing the need for communicating with remote systems and placing all resources within their infrastructure. Systems operating in a manner where access to external resources is completely restricted is known as running in a disconnected environment. OpenShift supports operating in a disconnected environment and cluster operators can take steps to prepare for normal operation. A full discussion on managing OpenShift in a disconnected environment is beyond the scope of this discussion, but can be found here. While there are several areas the must be accounted for when operating in a disconnected environment, having access to the container images that reside in external image registries is essential. The CDK, like the full platform is driven by container images sourced from external locations. Fortunately, the CDK does contain the functionality to specify an alternate location for which images that control the execution can originate from.

OpenShift’s container images are stored by default in the Red Hat Container Catalog (RHCC). Many organizations operate their own container registry internally for providing content either from remote locations or created in house. Common registry examples in use include a standalone docker registry (docker distribution), Sonatype Nexus, JFrog Artifactory and Red Hat Quay. Since the same container images that are used by OpenShift Container Platform are used by the CDK, organizations can serve them using an internal registry and satisfy both sets of consumers. One requirement that must be adhered to is that the name of the image repository, name and tag must match the source from the Red Hat Container Catalog (it can differ, however several manual changes would then be required).

export MINISHIFT_ENABLE_EXPERIMENTAL=y

With experimental features enabled, the CDK can now be started. For this example, let’s assume that there is an image registry located at registry.mycorp.com which has been seeded with the images to support OpenShift. Execute the following command to utilize the CDK with images sourced from this internal registry:

minishift start --insecure-registry registry.mycorp.com --docker-opt add-registry=registry.mycorp.com --docker-opt block-registry=registry.access.redhat.com --extra-clusterup-flags --image=registry.mycorp.com/openshift3/ose

Note: Concepts from both prior blogs on Proxies and Registration can also be used when running in a fully disconnected environment.

Note: Due to a regression in version 3.4 of the CDK, the –extra-clusterup-flags parameter is not accepted

Phew, that was a long command. Let’s take a moment to break it down.

  • minishift start

This is the primary command and subcommand used to start the CDK

  • –insecure-registry registry.mycorp.com

While the registry may be served using trusted SSL certificates, many organizations have their own Certificate Authority instead of leveraging a public CA, such as Comodo. Since the VM running the CDK only trusts certificates from public CA’s, this will allow docker to be able to communicate with the registry

  • –docker-opt add-registry= registry.mycorp.com

Many OpenShift components do not include the registry portion of the image and instead rely on the configuration of the underlying Docker daemon to provide a default set of registries to use. Both the OpenShift Container Platform and the Container Development Kit have the RHCC configured by default. By specifying the location of the internal registry, the CDK will be able to reference it when images are specified without the value of the registry.

  • –docker-opt block-registry=registry.access.redhat.com

To ensure images are only being sourced from the corporate registry not the default location (RHCC), the CDK VM can be configured to place a restriction at the docker daemon level.

  • –extra-clusterup-flags –image= registry.mycorp.com/openshift3/ose

OpenShift in the context of the CDK as of OpenShift version 3.9 utilizes the same image as containerized installation and contains all of the necessary logic to manage an OpenShift cluster. Under the covers of the CDK, the “oc cluster up” utility is leveraged to deploy OpenShift. By default, “oc cluster up” references the full path of the image, including registry. This experimental feature flag allows this value to be overridden with the location of the image from the enterprise registry.

The CDK will now start by pulling the container image and once this image is started, all dependent images by the platform will be retrieve. After the CDK has started fully, verify all running images are using the enterprise container registry.

First, check the names of the images currently running at a Docker level using the minishift ssh command:

minishift ssh "docker images --format '{{.Repository}}:{{.Tag}}'"

The final component that requires modification to support leveraging an enterprise registry is to update all of the ImageStreams that are populated in OpenShift. By default, they reference images from the RHCC. The Ansible based OpenShift installer does contain logic to update ImageStreams if the location differs from the RHCC. Unfortunately, the CDK does not contain this logic. Fortunately, this issue can be corrected with only a few commands.

First, make sure you are logged into OpenShift as a user with `cluster-admin` rights. By default, the `admin` user contains these privileges.

oc login -u admin

Similar to all other accounts in the CDK, any password can be specified.

Next replace the RHCC with the location of the enterprise registry for all ImageStreams by executing the following command:

oc get is -n openshift -o json | sed -e 's|registry.access.redhat.com|registry.mycorp.com|g' | oc replace -n openshift -f-

Make sure to replace registry.mycorp.com with the address of the enterprise registry.

With the ImageStreams now utilizing all of the enterprise registry as the source, reimport all of the ImageStreams:

for x in `oc get is -n openshift -o name`; do oc import-image $x -n openshift --all --insecure=true; done

After the command completes, all ImageStreams will be updated.

At this point the CDK is fully functional with images being referenced from the enterprise registry, thus enabling productivity in environments where security is a high priority.