Unable to Start Instance With Error "Cannot allocate memory"

Problem

Starting an instance from a SHUTDOWN state results in the following error being observed in the pf9-ostackhost log located under /var/log/pf9 directory.

Environment

• Platform9 Managed OpenStack - All versions

• Nova

• Libvirt

Cause

The instance fails to start because the libvirt process is not able to allocate the required memory being requested by the instance.

Resolution

1. Try migrating a few running instances to a different host.

2. If there is no hosts available to accommodate the running VMs, provision additional physical memory on the host.