[stable/zed] Add evacuate notes (#1206)
This is an automated cherry-pick of #1205
/assign mnaser
diff --git a/doc/source/admin/maintenance.rst b/doc/source/admin/maintenance.rst
index 362b152..f1998c8 100644
--- a/doc/source/admin/maintenance.rst
+++ b/doc/source/admin/maintenance.rst
@@ -5,6 +5,90 @@
This guide provides instructions for regular maintenance tasks necessary to
ensure the smooth and secure operation of the system.
+********************************
+Evacuating Nodes for Maintenance
+********************************
+
+When you need to perform maintenance on a node, you will need to evacuate the
+node to ensure that no workloads are running on it. Depending on the type of
+node you are evacuating, you will need to use different commands.
+
+Control Plane Node
+==================
+
+To evacuate a control plane node, you will need to drain the node. This will
+cause all the control plane components to be moved to other nodes in the
+cluster. To drain a control plane node, run the following command against
+the node you want to drain:
+
+.. code-block:: console
+
+ $ kubectl drain <node-name> --ignore-daemonsets --delete-local-data <node-name>
+
+In the example above, you would replace ``<node-name>`` with the name of the
+node you want to drain. Once this process is complete, you can safely perform
+maintenance on the node.
+
+When you are done with the maintenance, you can uncordon the node by running
+the following command:
+
+.. code-block:: console
+
+ $ kubectl uncordon <node-name>
+
+Compute Node
+============
+
+In order to evacuate a compute node, you will need to start by disabling the
+OpenStack compute service on the node. This will prevent new workloads from
+being scheduled on the node. To disable the OpenStack compute service, run
+the following command against the node you want to evacuate:
+
+.. code-block:: console
+
+ $ openstack compute service set --disable <node-name> nova-compute
+
+In the example above, you would replace ``<node-name>`` with the name of the
+node you want to evacuate. Once the OpenStack compute service has been
+disabled, you will need to evacuate all the virtual machines running on the
+node. To do this, run the following command:
+
+.. code-block:: console
+
+ $ nova host-evacuate-live <node-name>
+
+In the example above, you would replace ``<node-name>`` with the name of the
+node you want to evacuate. This command will live migrate all the virtual
+machines running on the node to other nodes in the cluster.
+
+.. admonition:: Note
+
+ It is generally not recommended to use the ``nova`` client however the
+ ``nova host-evacuate-live`` command is not available in the ``openstack``
+ client (see `bug 2055552 <https://bugs.launchpad.net/python-openstackclient/+bug/2055552>`_).
+
+You can monitor the progress of this operation by seeing if there are any VMs
+left on the node by running the following command:
+
+.. code-block:: console
+
+ $ openstack server list --host <node-name>
+
+Once all the virtual machines have been evacuated, you can safely perform
+maintenance on the node. When you are done with the maintenance, you can
+reenable the OpenStack compute service by running the following command:
+
+.. code-block:: console
+
+ $ openstack compute service set --enable <node-name> nova-compute
+
+.. admonition:: Note
+
+ Once you enable the compute service, the node will start accepting new
+ VMs but it will not automatically move the VMs back to the node. You will
+ need to manually move the VMs back to the node if you want them to run
+ there.
+
*********************
Renewing Certificates
*********************