Chapter 5. Red Hat OpenShift installation planning and considerations 81
5.3.2  Design considerations
This section discusses some design considerations.
PowerVC considerations
IBM PowerVC is an advanced virtualization and cloud management offering for IBM Power 
Systems. Built on OpenStack, it provides comprehensive virtualization management and 
cloud deployments for IBM AIX, IBM i, and Linux virtual machines (VMs). PowerVC simplifies 
the lifecycle management of the virtualization for Power Systems. It includes a deep 
integration with IBM PowerVM virtualization technologies.
Availability zones (host groups)
Host groups, also known as host aggregates in OpenStack’s terminology, allow you to create 
virtual boundaries around a group of hosts. It is a logical group of hosts, regardless of any 
features that they might or might not have in common. For example, the hosts feature the 
same architecture, network configuration, or storage, or hosts in the same rack or data center.
When a host group is created by using the user interface, an availability zone with the same 
name is created and assigned to the host group. PowerVC also supports the standard 
OpenStack APIs for host groups and availability zones.
Host groups (availability zones) include the following features:
/SM590000Every host must be in a host group
Any hosts that do not belong to a user-defined host group are members of the default host 
group. The default host group cannot be deleted.
/SM590000Virtual machines are kept within the host group
A virtual machine can be deployed to a specific host or to a host group. After deployment, 
that virtual machine must always be migrated or remote restarted within the host group.
/SM590000Placement policies are associated with host groups
Every host within a host group is subject to the host group’s placement policy. The default 
placement policy is striping.
/SM590000Automated Remote Restart
If enabled, the PowerVC monitors hosts for failure by using the Platform Resource 
Scheduler (PRS) HA service. If a host fails, PowerVC automatically remote restarts the 
VMs from the failed host to another host within a host group.
/SM590000Dynamic Resource Optimizer (DRO)
If enabled, DRO continuously monitors your cloud environment’s usage. You can specify 
that DRO monitors CPU usage or available memory. When a host is found to be overused, 
the DRO attempts to correct the situation by performing the action that you specified. It 
can migrate VMs to another host within a host group or, when applicable, work with 
Capacity on Demand (CoD) to activate mobile cores.
Note: A host can belong only to one host group (availability zone).