Fill out OCP 3.4 release notes

Author: adellape

Diff for: _topic_map.yml

@@ -660,8 +660,6 @@ Topics:
     File: daemonsets
   - Name: Pod Autoscaling
     File: pod_autoscaling
-  - Name: Pod Disruption Budget
-    File: pod_disruption_budget
   - Name: Managing Volumes
     File: volumes
   - Name: Using Persistent Volumes

Diff for: admin_guide/managing_pods.adoc

@@ -403,3 +403,76 @@ annotations. For example, to limit both pod egress and ingress bandwidth to 10M/
 ----
 oc create -f <file_or_dir_path>
 ----
+
+[[managing-pods-poddisruptionbudget]]
+== Setting Pod Disruption Budgets
+
+A _pod disruption budget_ is part of the
+link:http://kubernetes.io/docs/admin/disruptions/[Kubernetes] API, which can be
+managed with `oc` commands like other
+xref:../cli_reference/basic_cli_operations.adoc#object-types[object types]. They
+allow the specification of safety constraints on pods during operations, such as
+draining a node for maintenance.
+
+ifdef::openshift-enterprise[]
+[NOTE]
+====
+Starting in {product-title} 3.4, pod disruption budgets is a feature in
+link:https://access.redhat.com/support/offerings/techpreview[Technology Preview], available only for users with *cluster-admin* privileges.
+====
+endif::[]
+
+`PodDisruptionBudget` is an API object that specifies the minimum number or
+percentage of replicas that must be up at a time. Setting these in projects can
+be helpful during node maintenance (such as scaling a cluster down or a cluster
+upgrade) and is only honored on voluntary evictions (not on node failures).
+
+A `PodDisruptionBudget` object's configuration consists of the following key
+parts:
+
+* A label selector, which is a label query over a set of pods.
+* An availability level, which specifies the minimum number of pods that must be
+ available simultaneously.
+
+The following is an example of a `PodDisruptionBudget` resource:
+
+====
+[source,yaml]
+----
+apiVersion: policy/v1alpha1 <1>
+kind: PodDisruptionBudget
+metadata:
+  name: my-pdb
+spec:
+  selector:  <2>
+    matchLabels:
+      foo: bar
+  minAvailable: 2  <3>
+----
+
+<1> `PodDisruptionBudget` is part of the `policy/v1alpha` API group.
+<2> A label query over a set of resources. The result of `matchLabels` and
+ `matchExpressions` are logically conjoined.
+<3> The minimum number of pods that must be available simultaneously. This can
+be either an integer or a string specifying a percentage (for example, `20%`).
+====
+
+If you created a YAML file with the above object definition, you could add it to project with the following:
+
+----
+$ oc create -f </path/to/file> -n <project_name>
+----
+
+You can check for pod disruption budgets across all projects with the following:
+
+----
+$ oc get poddisruptionbudget --all-namespaces
+
+NAMESPACE         NAME          MIN-AVAILABLE   SELECTOR
+another-project   another-pdb   4               bar=foo
+test-project      my-pdb        2               foo=bar
+----
+
+The `PodDisruptionBudget` is considered healthy when there are at least
+`minAvailable` pods running in the system. Every pod above that limit can be
+xref:../admin_guide/out_of_resource_handling.adoc#out-of-resource-eviction-policy[evicted].