Draft Document for Review December 11, 2019 1:55 pm 8459ch05.fm the lifecycle management of the virtualization for Power Systems, it has 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 do have the  same architecture, network configuration, or storage, or hosts in the same rack or datacenter. When a host group is created through 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) have the following features: GLYPH<SM590000> Every 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. GLYPH<SM590000> Virtual 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. GLYPH<SM590000> Placement 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. GLYPH<SM590000> Automated Remote Restart . If is 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. GLYPH<SM590000> Dynamic Resource Optimizer (DRO) . If is 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 tries 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. Chapter 5. Red Hat OpenShift installation planning and considerations  77 Note:  A host can only belong to one host group (availability zone).