Libvirt

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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

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