[OSDOCS-13450]: Isolation details for HCP

Author: lahinson

hosted_control_planes/hcp-prepare/hcp-distribute-workloads.adoc

@@ -10,11 +10,11 @@ Before you get started with {hcp} for {product-title}, you must properly label n
 
 * To ensure high availability and proper workload deployment. For example, you can set the `node-role.kubernetes.io/infra` label to avoid having the control-plane workload count toward your {product-title} subscription.
 * To ensure that control plane workloads are separate from other workloads in the management cluster.
-//lahinson - sept. 2023 - commenting out the following lines until those levels are supported for self-managed hypershift
-//* To ensure that control plane workloads are configured at one of the following multi-tenancy distribution levels:
-//** Everything shared: Control planes for hosted clusters can run on any node that is designated for control planes.
-//** Request serving isolation: Serving pods are requested in their own dedicated nodes.
-//** Nothing shared: Every control plane has its own dedicated nodes.
+* To ensure that control plane workloads are configured at one of the following multi-tenancy distribution levels:
+
+** Everything shared: Control planes for hosted clusters can run on any node that is designated for control planes.
+** Request serving isolation: Serving pods are requested in their own dedicated nodes.
+** Nothing shared: Every control plane has its own dedicated nodes.
 
 [IMPORTANT]
 ====
@@ -24,3 +24,4 @@ Do not use the management cluster for your workload. Workloads must not run on n
 include::modules/hcp-labels-taints.adoc[leveloffset=+1]
 include::modules/hcp-priority-classes.adoc[leveloffset=+1]
 include::modules/hcp-virt-taints-tolerations.adoc[leveloffset=+1]
+include::modules/hcp-isolation.adoc[leveloffset=+1]

modules/hcp-isolation.adoc

@@ -0,0 +1,42 @@
+// Module included in the following assemblies:
+//
+// * hosted_control_planes/hcp-prepare/hcp-distribute-workloads.adoc
+
+:_mod-docs-content-type: CONCEPT
+[id="hcp-isolation_{context}"]
+= Control plane isolation
+
+You can configure {hcp} to isolate network traffic or control plane pods.
+
+== Network policy isolation
+
+Each hosted control plane is assigned to run in a dedicated Kubernetes namespace. By default, the Kubernetes namespace denies all network traffic.
+
+The following network traffic is allowed through the network policy that is enforced by the Kubernetes Container Network Interface (CNI):
+
+* Ingress pod-to-pod communication in the same namespace (intra-tenant)
+* Ingress on port 6443 to the hosted `kube-apiserver` pod for the tenant
+* Metric scraping from the management cluster Kubernetes namespace with the `network.openshift.io/policy-group: monitoring` label is allowed for monitoring
+
+== Control plane pod isolation
+
+In addition to network policies, each hosted control plane pod is run with the `restricted` security context constraint. This policy denies access to all host features and requires pods to be run with a UID and with SELinux context that is allocated uniquely to each namespace that hosts a customer control plane.  
+
+The policy ensures the following constraints:
+* Pods cannot run as privileged.
+* Pods cannot mount host directory volumes.
+* Pods must run as a user in a pre-allocated range of UIDs.  
+* Pods must run with a pre-allocated MCS label.
+* Pods cannot access the host network namespace.
+* Pods cannot expose host network ports.
+* Pods cannot access the host PID namespace.  
+* By default, pods drop the following Linux capabilities: `KILL`, `MKNOD`, `SETUID`, and `SETGID`.
+
+The management components, such as `kubelet` and `crio`, on each management cluster worker node are protected by an SELinux label that is not accessible to the SELinux context for pods that support {hcp}.
+
+The following SELinux labels are used for key processes and sockets:
+
+* *kubelet*: `system_u:system_r:unconfined_service_t:s0`
+* *crio*: `system_u:system_r:container_runtime_t:s0`
+* *crio.sock*: `system_u:object_r:container_var_run_t:s0` 
+* *<example user container processes>*: `system_u:system_r:container_t:s0:c14,c24`