Add high level documentation for disconnected envs

Signed-off-by: Brendan Shephard <[email protected]>

docs/assemblies/proc_deploying-in-disconnected-environments.adoc

@@ -0,0 +1,46 @@
+[id="proc_deploying-in-disconnected-environments"]
+= Deploying OpenStack in a disconnected environment
+
+[role="_abstract"]
+Deploying in diconnected environments can be achieved largely by following the OpenShift documentation for mirroring OLM Operators: https://docs.openshift.com/container-platform/4.17/disconnected/mirroring/installing-mirroring-installation-images.html#olm-mirror-catalog_installing-mirroring-installation-images
+
+The `openstack-operator` contains a list of related images that will ensure all required images for the deployment are mirrored following the above OpenShift process. Once images are mirrored, the `ImageContentSourcePolicy` custom resource (CR) is created. This process results in the `machine-config-operator` rendering a `MachineConfig` called `99-master-genereted-registries`. This `MachineConfig` contains a `registries.conf` file that is applied to all of the OpenShift nodes in the cluster.
+
+In order to integrate cleanly with this process. The dataplane controller will check for the existence of the `ImageContentSourcePolicy`. If one is found, we will read the `registries.conf` file from the `99-master-generated-registries` `MachineConfig`. The dataplane controller will then set two variables in the Ansible inventory for the nodes.
+
+[,yaml]
+----
+        edpm_podman_disconnected_ocp: true
+        edpm_podman_registries_conf: |
+----
+
+`edpm_podman_disconnected_ocp` is used to conditionally render `registries.conf` on the dataplane nodes during the deployment. While `edpm_podman_registries_conf` is the contents of the `registries.conf` that we acquired from the `MachineConfig` in the cluster.
+
+This ensures that our EDPM nodes are configured in a consistent manner with the OpenShift nodes.
+
+These mirrors are configured to work specifically with image digests rather than tags:
+
+[,yaml]
+----
+        edpm_podman_registries_conf: |
+            unqualified-search-registries = ["registry.access.redhat.com", "docker.io"]
+            short-name-mode = ""
+
+            [[registry]]
+              prefix = ""
+              location = "gcr.io/kubebuilder/kube-rbac-proxy"
+
+              [[registry.mirror]]
+                location = "quay-mirror-registry.example.net:8443/olm/kubebuilder-kube-rbac-proxy"
+                pull-from-mirror = "digest-only"
+----
+
+We can see that the `pull-from-mirror` parameter is set to `digest-only`. This means that any attempt by podman to pull an image by a digest will result in the image being pulled from the specified mirror.
+
+Accordingly, we can see that image references in the `OpenStackVersion` CR are provided in the digest format, for example the multipathd image:
+
+[,bash]
+----
+$ oc get openstackversion -o yaml | yq '.items[].status.containerImages.edpmMultipathdImage'
+"quay.io/podified-antelope-centos9/openstack-multipathd@sha256:7df2e1ebe4ec6815173e49157848a63d28a64ffb0db8de6562c4633c0fbcdf3f"
+----