Virtualization Driver 4.4

The component that deals with the hypervisor to create, manage and get information about virtual machine objects is called Virtual Machine Manager (VMM for short). This component has two parts. The first one resides in the core and holds most of the general functionality common to all the drivers (and some specific), the second is the driver that is the one able to translate basic VMM actions to the hypervisor.

inlinetoc

Driver Configuration

There are two main drivers one_vmm_exec and one_vmm_sh. Both take commands from OpenNebula and execute a set of scripts for those actions, the main difference is that one_vmm_exec executes the commands remotely (logging into the host where VM is being or is going to be executed) and one_vmm_sh does the execution of the scripts in the frontend.

The driver takes some parameters, described here:

parameter description
-r <num> number of retries when executing an action
-t <num number of threads, i.e. number of actions done at the same time
-l <actions> (one_vmm_exec only) actions executed locally, command can be overridden for each action
<driver_directory> where in the remotes directory the driver can find the action scripts

These are the actions valid in the -l parameter:

  • attach_disk
  • attach_nic
  • cancel
  • deploy
  • detach_disk
  • detach_nic
  • kvmrc
  • migrate
  • migrate_local
  • poll
  • reboot
  • reset
  • restore
  • save
  • shutdown
  • snapshot_create
  • snapshot_delete
  • snapshot_revert

You can also provide an alternative script name for local execution, by default the script is called the same as the action, in this fashion action=script_name. As an example: 

-l migrate,poll=poll_ganglia,save

These arguments are specified in the oned.conf file, arguments variable: 

VM_MAD = [
    name       = "kvm",
    executable = "one_vmm_exec",
    arguments  = "-t 15 -r 0 -l migrate,save kvm",
    default    = "vmm_exec/vmm_exec_kvm.conf",
    type       = "kvm" ]

Actions

Every action should have an executable program (mainly scripts) located in the remote dir (remotes/vmm/<driver_directory>) that performs the desired action. These scripts receive some parameters (and in the case of DEPLOY also STDIN) and give back the error message or information in some cases writing to STDOUT.

VMM actions, they are the same as the names of the scripts:

  • attach_disk: Attaches a new DISK in the VM
    • Arguments
      • DOMAIN: Domain name: one-101
      • SOURCE: Image path
      • TARGET: Device in the guest: hda, sdc, vda, xvdc
      • TARGET_INDEX: Position in the list of disks
      • DRV_ACTION: action xml. Base: /VMM_DRIVER_ACTION_DATA/VM/TEMPLATE/DISK[ATTACH='YES']
        • DRIVER: Disk format: raw, qcow2
        • TYPE: Disk type: block, cdrom, rbd, fs or swap
        • READONLY: The value is YES when it's read only
        • CACHE: Cache mode: none, writethrough, writeback
        • SOURCE: Image source, used for ceph
    • Response
      • Success: -
      • Faulure: Error message
  • attach_nic: Attaches a new NIC in the VM
    • Arguments
      • DOMAIN: Domain name: one-808
      • MAC: MAC address of the new NIC
      • BRIDGE: Bridge where to attach the new NIC
      • MODEL: NIC model to emulate, ex: e1000
      • NET_DRV: Network driver used, ex: ovswitch
    • Response
      • Success: -
      • Failure: Error message
  • cancel: Destroy a VM
    • Arguments:
      • DOMAIN: Domain name: one-909
    • Response
      • Success: -
      • Failure: Error message
  • deploy: Deploy a new VM
    • Arguments:
      • DEPLOYMENT_FILE: where to write de deployment file. You have to write whatever comes from STDIN to a file named like this parameter. In shell script you can do: cat > $domain
    • Response
      • Success: Deploy id, ex: one-303
      • Failure: Error message
  • detach_disk: Detaches a DISK from a VM
    • Arguments
      • DOMAIN: Domain name: one-286
      • SOURCE: Image path
      • TARGET: Device in the guest: hda, sdc, vda, xvdc
      • TARGET_INDEX: Position in the list of disks
    • Response
      • Success: -
      • Failure: Error message
  • detach_nic: Detaches a NIC from a VM
    • Arguments
      • DOMAIN: Domain name: one-286
      • MAC: MAC address of the NIC to detach
    • Response
      • Success: -
      • Failure: Error message
  • migrate: Live migrate a VM to another host
    • Arguments:
      • DOMAIN: Domain name: one-286
      • DESTINATION_HOST: Host where to migrate the VM
      • HOST: Host where the VM is currently running
    • Response
      • Success: -
      • Failure: Error message
  • poll: Get information from a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • HOST: Host where the VM is running
    • Response
      • Success: -
      • Failure: Error message
  • reboot: Orderly reboots a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • HOST: Host where the VM is running
    • Response
      • Success: -
      • Failure: Error message
  • reset: Hard reboots a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • HOST: Host where the VM is running
    • Response
      • Success: -
      • Failure: Error message
  • restore: Restores a previously saved VM
    • Arguments:
      • FILE: VM save file
      • HOST: Host where to restore the VM
    • Response
      • Success: -
      • Failure: Error message
  • save: Saves a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • FILE: VM save file
      • HOST: Host where the VM is running
    • Response
      • Success: -
      • Failure: Error message
  • shutdown: Orderly shutdowns a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • HOST: Host where the VM is running
    • Response
      • Success: -
      • Failure: Error message
  • snapshot_create: Makes a new snapshot of a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • ONE_SNAPSHOT_ID: OpenNebula snapshot identifier
    • Response
      • Success: Snapshot name for the hypervisor. Used later to delete or revert
      • Failure: Error message
  • snapshot_delete: Deletes a snapshot of a VM
    • Arguments:
      • DOMAIN: Domain name: one-286
      • SNAPSHOT_NAME: Name used to refer the snapshot in the hypervisor
    • Response
      • Success: -
      • Failure: Error message
  • snapshot_revert: Returns a VM to an saved state
    • Arguments:
      • DOMAIN: Domain name: one-286
      • SNAPSHOT_NAME: Name used to refer the snapshot in the hypervisor
    • Response
      • Success: -
      • Failure: Error message

action xml parameter is a base64 encoded xml that holds information about the VM. To get one of the values explained in the documentation, for example from attach_disk READONLY you can add to the base XPATH the name of the parameter. XPATH: 

/VMM_DRIVER_ACTION_DATA/VM/TEMPLATE/DISK[ATTACH='YES']/READONLY

When using shell script there is a handy script that gets parameters for given XPATH in that XML. Example: 

XPATH="${DRIVER_PATH}/../../datastore/xpath.rb -b $DRV_ACTION"
 
unset i j XPATH_ELEMENTS
 
DISK_XPATH="/VMM_DRIVER_ACTION_DATA/VM/TEMPLATE/DISK[ATTACH='YES']"
 
while IFS= read -r -d '' element; do
    XPATH_ELEMENTS[i++]="$element"
done < <($XPATH     $DISK_XPATH/DRIVER \
                    $DISK_XPATH/TYPE \
                    $DISK_XPATH/READONLY \
                    $DISK_XPATH/CACHE \
                    $DISK_XPATH/SOURCE)
 
DRIVER="${XPATH_ELEMENTS[j++]:-$DEFAULT_TYPE}"
TYPE="${XPATH_ELEMENTS[j++]}"
READONLY="${XPATH_ELEMENTS[j++]}"
CACHE="${XPATH_ELEMENTS[j++]}"
IMG_SRC="${XPATH_ELEMENTS[j++]}"

one_vmm_sh has the same script actions and meanings but an argument more that is the host where the action is going to be performed. This argument is always the first one. If you use -p parameter in one_vmm_ssh the poll action script is called with one more argument that is the host where the VM resides, also it is the same parameter.

Poll Information

POLL is the action that gets monitoring info from the running VMs. The format it is supposed to give back information is a line with KEY=VALUE pairs separated by spaces. Like this: 

STATE=a USEDMEMORY=554632

The poll action can give back any information and it will be added to the VM information hold but there are some variables that should be given back as they are meaningful to OpenNebula:

Variable Description
STATE State of the VM (explained later)
USEDCPU Percentage of 1 CPU consumed (two fully consumed cpu is 200)
USEDMEMORY Memory consumption in kilobytes
NETRX Received bytes from the network
NETTX Sent bytes to the network

STATE is a single character that tells OpenNebula the status of the VM, the states are the ones in this table:

statedescription
-Detecting state error. The monitoring could be done, but it returned an unexpected output.
aActive. The VM is alive, but not necessary running. Could be blocked, booting, etc.
pPaused. Self-explanatory.
eError. The VM crashed or somehow its deployment failed.
dDisappeared. The VM is not known by the hypervisor anymore.

Deployment File

The deployment file is a text file written by OpenNebula core that holds the information of a VM. It is used when deploying a new VM. OpenNebula is able to generate three formats of deployment files:

  • xen: deployment file suitable to be used with xen tools
  • kvm: libvirt format used to create kvm VMs
  • xml: xml representation of the VM

If the target hypervisor is not xen nor libvirt/kvm the best format to use is xml as it holds more information than the two others. It has all the template information encoded as xml. This is an example: 

    <TEMPLATE>
      <CPU><![CDATA[1.0]]></CPU>
      <DISK>
        <DISK_ID><![CDATA[0]]></DISK_ID>
        <SOURCE><![CDATA[/home/user/vm.img]]></SOURCE>
        <TARGET><![CDATA[sda]]></TARGET>
      </DISK>
      <MEMORY><![CDATA[512]]></MEMORY>
      <NAME><![CDATA[test]]></NAME>
      <VMID><![CDATA[0]]></VMID>
    </TEMPLATE>

There are some information added by OpenNebula itself like the VMID and the DISK_ID for each disk. DISK_ID is very important as the disk images are previously manipulated by the TM driver and the disk should be accessible at VM_DIR/VMID/images/disk.DISK_ID.