How can I define flavor vCPU topology?

You can define flavor vCPU topology, for example, you can prevent a flavor from exceeding 2 sockets but still have 4 cores, on any Juno or higher stack, as noted at Virt driver guest vCPU topology configuration.

Use these commands:

nova flavor-create m1.windowsdesktop auto 8192 40 4
nova flavor-key m1.windowsdesktop set hw:cpu_max_sockets=2
nova flavor-list --extra-specs

The virtualization driver will calculate the exact number of cores/sockets/threads based on the flavor vCPU count and this maximum sockets constraint.

You can define:

• hw:cpu_sockets=NN - preferred number of sockets to expose to the guest
• hw:cpu_cores=NN - preferred number of cores to expose to the guest
• hw:cpu_threads=NN - preferred number of threads to expose to the guest
• hw:cpu_max_sockets=NN - maximum number of sockets to expose to the guest
• hw:cpu_max_cores=NN - maximum number of cores to expose to the guest
• hw:cpu_max_threads=NN - maximum number of threads to expose to the guest