Libvirt

1. Libvirt Python API

• Compute manager calls the driver
• `self.driven.pause(instance)`
• It will suspend the instance
• Nova Libvirt Driver

2. Libvirt Domain 

• Libvirt domains are defined via XML
• Domains defined by Nova are persistent
• XML is re-generated on Hard Reboot
• Manual costomerizations will be overriden
• Logging occurs per-domain
• /var/log/libvirt/qemu/instance_name.log

3. Virsh 

• virsh is the command line tool for Libvirt
• Consumes the same API referenced earlier via C
• virsh list
• List all domains by name
• virsh domname uuid
• Returns the instance_name
• virsh dumpxml uuid
• Configuration for an individual domain

4.  Libvirt Domain XML

• Translated by Libvirt to ultimately call QEMU with the right arguments
• The XML generated by Nova ends up being modified, fairly heavility, by Libvirt upon definition
• Key difference between "active" and "inactive" XML
• Numerous values are derived at time of instance start
• Output from an active "dumpxml" will likely fail to define
• Use `virsh dumpxml --inactive uuid `

5. Libvirtd Configuration

• Critically important information tuning for Libvirt 1.1.x and newer, example
• max_clients = 50