VMPlacement

VMPlacement is the process of selecting a physical host for a virtual machine within a virtualization cluster. It encompasses the evaluation of available resources, constraints, and policies to determine where to instantiate or migrate a VM. The aim is to satisfy the VM’s resource requirements (CPU, memory, storage I/O, and network capacity) while balancing load, meeting service-level objectives, and reducing operational costs. Placement decisions occur at VM creation and during ongoing management through live migration and rebalancing.

Key factors include resource capacity and utilization, NUMA locality, storage and network topology, and hardware features such as GPUs or PCI devices. Affinity rules (co-locate related VMs) and anti-affinity rules (separate VMs for fault tolerance) influence placement. Licensing constraints, maintenance windows, and power considerations can also shape decisions. Reliability and fault domains, such as rack or blade server boundaries, may be taken into account to improve availability.

Common approaches employ scheduling algorithms that trade off consolidation against performance. Bin-packing strategies try to minimize the number of hosts used, while load-balancing aims to distribute VMs evenly. Many platforms offer automation through a built-in placement engine, sometimes called a scheduler or distributed resource scheduler, that continuously evaluates the cluster state and migrates VMs to satisfy policies. Examples include VMware vSphere DRS, OpenStack Nova scheduler, and other cloud or virtualization platforms.