[Microstack] Overcommit Resources

Overcommit hypervisor and allocate more resources.

Just like Kubernetes's resource policy (requests and limits), OpenStack offers us options to overcommit. You can achieve this by using aggregate option.

Create Aggregation

microstack.openstack aggregate create extra-resources

This command will generate an aggregation named extra-resources.

Add Host to Aggregation

microstack.openstack aggregate add host extra-resources openstack

This command will allow the extra-resources aggregation connected to host named openstack. Then you can check if it was successfully set or not by

microstack.openstack aggregate show extra-resources

An example output will be:

+-------------------+-----------------------------------------------------------------------------------------------------------+
| Field             | Value                                                                                                     |
+-------------------+-----------------------------------------------------------------------------------------------------------+
| availability_zone | None                                                                                                      |
| created_at        | 2023-02-15T04:20:05.000000                                                                                |
| deleted           | False                                                                                                     |
| deleted_at        | None                                                                                                      |
| hosts             | openstack                                                                                                 |
| id                | 1                                                                                                         |
| name              | extra-resources                                                                                           |
| properties        |                                                                                                           |
| updated_at        | None                                                                                                      |
+-------------------+-----------------------------------------------------------------------------------------------------------+

As you can see, the host openstack was set as aggregation for extra-resources.

Set Property to Aggregation

openstack aggregate set --property cpu_allocation_ratio=2.0 extra-resources

You can apply 2x times vCPU than the physical CPU using cpu_allocation_ratio. There are a choice of options to use:

• cpu_allocation_ratio: This property sets the CPU allocation ratio for the hypervisor(s) in the aggregate. The CPU allocation ratio is the ratio of virtual CPU (vCPU) to physical CPU (pCPU) on the host. For example, setting --property cpu_allocation_ratio=2.0 doubles the amount of virtual CPU available to instances running on the hypervisor(s) in the aggregate.

• ram_allocation_ratio: This property sets the RAM allocation ratio for the hypervisor(s) in the aggregate. The RAM allocation ratio is the ratio of virtual RAM to physical RAM on the host. For example, setting --property ram_allocation_ratio=2.0 doubles the amount of virtual RAM available to instances running on the hypervisor(s) in the aggregate.

• disk_allocation_ratio: This property sets the disk allocation ratio for the hypervisor(s) in the aggregate. The disk allocation ratio is the ratio of virtual disk to physical disk on the host. For example, setting --property disk_allocation_ratio=2.0 doubles the amount of virtual disk available to instances running on the hypervisor(s) in the aggregate.

• availability_zone: This property sets the availability zone for the hypervisor(s) in the aggregate. The availability zone is a logical partition of the OpenStack environment that separates resources and isolates failure domains. For example, setting --property availability_zone=zone1 assigns the hypervisor(s) in the aggregate to the "zone1" availability zone.

• pci_passthrough_whitelist: This property sets a whitelist of PCI devices that are passed through to instances running on the hypervisor(s) in the aggregate. For example, setting --property pci_passthrough_whitelist="{"vendor_id":"8086","product_id":"100e"}" passes through PCI devices with a vendor ID of "8086" and a product ID of "100e" to instances running on the hypervisor(s) in the aggregate.

Openstack recommends overcommiting CPU ration 16, and RAM ratio as 1.5 according to here.

Creating Flavor for Aggregate

Also create flavor for aggregation by following command:

openstack flavor create --ram 8192 --disk 10 --vcpus 4 small-disk

Then apply aggregate extra-resources to small-disk using:

openstack aggregate set --property flavor=extra-large extra-resources