// Module included in the following assemblies:
//
// * machine_management/control_plane_machine_management/cpmso-configuration.adoc

:_mod-docs-content-type: PROCEDURE
[id="cpmso-config-prefix_{context}"]
= Adding a custom prefix to control plane machine names

[role="_abstract"]
Customize the prefix of control plane machine names to distinguish machines across environments or match your naming conventions.

.Procedure

. Edit the `ControlPlaneMachineSet` CR by running the following command:
+
[source,terminal]
----
$ oc edit controlplanemachineset.machine.openshift.io cluster \
  -n openshift-machine-api
----

. Edit the `.spec.machineNamePrefix` field of the `ControlPlaneMachineSet` CR:
+
[source,yaml]
----
apiVersion: machine.openshift.io/v1
kind: ControlPlaneMachineSet
metadata:
  name: cluster
  namespace: openshift-machine-api
spec:
  machineNamePrefix: <machine_prefix>
# ...
----
+
where `<machine_prefix>` specifies a prefix name that follows the requirements for a lowercase RFC 1123 subdomain.
+
[IMPORTANT]
====
A lowercase RFC 1123 subdomain must consist of only lowercase alphanumeric characters, hyphens ('-'), and periods ('.').
Each block, separated by periods, must start and end with an alphanumeric character.
Hyphens are not allowed at the start or end of a block, and consecutive periods are not permitted.
====

. Save your changes.

.Next steps

* If you changed only the value of the `machineNamePrefix` parameter, clusters that use the default `RollingUpdate` update strategy are not automatically updated.
To propagate this change, you must replace your control plane machines manually, regardless of the update strategy for the cluster.
For more information, see "Replacing a control plane machine".