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

:_mod-docs-content-type: CONCEPT
[id="cpmso-failure-domains-balancing_{context}"]
= Balancing control plane machines

[role="_abstract"]
The control plane machine set balances control plane machines across failure domains to ensure fault tolerance and high availability.

//If failure domains must be reused, they are selected alphabetically by name.
When possible, the control plane machine set uses each failure domain equally to ensure appropriate fault tolerance. If there are fewer failure domains than control plane machines, failure domains are selected for reuse alphabetically by name. For clusters with no failure domains specified, all control plane machines are placed within a single failure domain.

Some changes to the failure domain configuration cause the control plane machine set to rebalance the control plane machines. For example, if you add failure domains to a cluster with fewer failure domains than control plane machines, the control plane machine set rebalances the machines across all available failure domains.