Revise cluster management task

After removing the sections of the page that are not in line with the
content guide, there is little left.

Edit pages that link to removed task to no longer link there.
Redirect using 302 status so that there is a future opportunity to reinstate
the page or something like it.

- Avoid links to removed cluster management task
- Broaden applicability of “Safely Drain A Node”
- Add (stub) cluster upgrade task page
- Add a basic page about upgrading your cluster.
- Add a task page about enabling or disabling HTTP APIs

content/en/docs/tasks/administer-cluster/safely-drain-node.md

@@ -4,14 +4,14 @@ reviewers:
 - mml
 - foxish
 - kow3ns
-title: Safely Drain a Node while Respecting the PodDisruptionBudget
+title: Safely Drain a Node
 content_type: task
 min-kubernetes-server-version: 1.5
 ---
 
 <!-- overview -->
 This page shows how to safely drain a {{< glossary_tooltip text="node" term_id="node" >}},
-respecting the PodDisruptionBudget you have defined.
+optionally respecting the PodDisruptionBudget you have defined.
 
 ## {{% heading "prerequisites" %}}
 
@@ -27,6 +27,15 @@ This task also assumes that you have met the following prerequisites:
 
 <!-- steps -->
 
+## (Optional) Configure a disruption budget {#configure-poddisruptionbudget}
+
+To endure that your workloads remain available during maintenance, you can
+configure a [PodDisruptionBudget](/docs/concepts/workloads/pods/disruptions/).
+
+If availability is important for any applications that run or could run on the node(s)
+that you are draining, [configure a PodDisruptionBudgets](/docs/tasks/run-application/configure-pdb/)
+first and the continue following this guide.
+
 ## Use `kubectl drain` to remove a node from service
 
 You can use `kubectl drain` to safely evict all of your pods from a
@@ -158,7 +167,4 @@ application owners and cluster owners to establish an agreement on behavior in t
 
 
 * Follow steps to protect your application by [configuring a Pod Disruption Budget](/docs/tasks/run-application/configure-pdb/).
-* Learn more about [maintenance on a node](/docs/tasks/administer-cluster/cluster-management/#maintenance-on-a-node).
-
-