Nova weigher (optional)

The Aicerine weigher is an optional, open-source Nova weigher. You do not need it: the lifecycle works through the Placement and Nova APIs alone.

When it helps

Live migration corrects a hot host after the fact. For VMs that cannot move, initial placement is the only chance to place them well:

• VMs on local disks;
• VMs with PCI passthrough;
• bursts of VM creation.

On those fleets, the weigher lets Nova's scheduler ask the appliance for a score on the hosts Nova already found admissible.

What it does and does not do

• It only weighs candidates Nova already filtered. It cannot add a host, remove one, or bypass a rule.
• Nova combines its score with its own weighers and keeps the final selection.
• When the appliance is late, unavailable or stopped, the weigher's contribution is neutral and Nova decides alone.

The weigher runs inside nova-scheduler, which the rest of Aicerine never does. That is why it is optional.

Documentation

The weigher's integration documentation is shared with pilot partners until the weigher is released: join the pilot program.