Virtual Machine Applications

The vm universe facilitates an HTCondor job that matches and then lands a disk image on an execute machine within an HTCondor pool. This disk image is intended to be a virtual machine. In this manner, the virtual machine is the job to be executed.

This section describes this type of HTCondor job. See Configuration File Entries Relating to Virtual Machines for details of configuration variables.

The Submit Description File

Different than all other universe jobs, the vm universe job specifies a disk image, not an executable. Therefore, the submit commands input, output, and error do not apply. If specified, condor_submit rejects the job with an error. The executable command changes definition within a vm universe job. It no longer specifies an executable file, but instead provides a string that identifies the job for tools such as condor_q. Other commands specific to the type of virtual machine software identify the disk image.

Xen and KVM virtual machine software are supported. As these differ from each other, the submit description file specifies one of

vm_type = xen

or

vm_type = kvm

The job is required to specify its memory needs for the disk image with vm_memory, which is given in Mbytes. HTCondor uses this number to assure a match with a machine that can provide the needed memory space.

Virtual machine networking is enabled with the command

vm_networking = true

And, when networking is enabled, a definition of vm_networking_type as bridge matches the job only with a machine that is configured to use bridge networking. A definition of vm_networking_type as nat matches the job only with a machine that is configured to use NAT networking. When no definition of vm_networking_type is given, HTCondor may match the job with a machine that enables networking, and further, the choice of bridge or NAT networking is determined by the machine’s configuration.

Modified disk images are transferred back to the machine from which the job was submitted as the vm universe job completes. Job completion for a vm universe job occurs when the virtual machine is shut down, and HTCondor notices (as the result of a periodic check on the state of the virtual machine). Should the job not want any files transferred back (modified or not), for example because the job explicitly transferred its own files, the submit command to prevent the transfer is

vm_no_output_vm = true

The required disk image must be identified for a virtual machine. This vm_disk command specifies a list of comma-separated files. Each disk file is specified by colon-separated fields. The first field is the path and file name of the disk file. The second field specifies the device. The third field specifies permissions, and the optional fourth specifies the format. Here is an example that identifies a single file:

vm_disk = swap.img:sda2:w:raw

If HTCondor will be transferring the disk file, then the file name given in vm_disk should not contain any path information. Otherwise, the full path to the file should be given.

Setting values in the submit description file for some commands have consequences for the virtual machine description file. These commands are

HTCondor uses these values when it produces the description file.

If any files need to be transferred from the access point to the machine where the vm universe job will execute, HTCondor must be explicitly told to do so with the standard file transfer attributes:

should_transfer_files = YES
when_to_transfer_output = ON_EXIT
transfer_input_files = /myxen/diskfile.img,/myxen/swap.img

Any and all needed files that will not accessible directly from the machines where the job may execute must be listed.

Further commands specify information that is specific to the virtual machine type targeted.

Xen-Specific Submit Commands

A Xen vm universe job requires specification of the guest kernel. The xen_kernel command accomplishes this, utilizing one of the following definitions.

  1. xen_kernel = included implies that the kernel is to be found in disk image given by the definition of the single file specified in vm_disk.

  2. xen_kernel = path-to-kernel gives the file name of the required kernel. If this kernel must be transferred to machine on which the vm universe job will execute, it must also be included in the transfer_input_files command.

    This form of the xen_kernel command also requires further definition of the xen_root command. xen_root defines the device containing files needed by root.

Checkpoints

Creating a checkpoint is straightforward for a virtual machine, as a checkpoint is a set of files that represent a snapshot of both disk image and memory. The checkpoint is created and all files are transferred back to the $(SPOOL) directory on the machine from which the job was submitted. The submit command to create checkpoints is

vm_checkpoint = true

Without this command, no checkpoints are created (by default). With the command, a checkpoint is created any time the vm universe jobs is evicted from the machine upon which it is executing. This occurs as a result of the machine configuration indicating that it will no longer execute this job.

Periodic creation of checkpoints is not supported at this time.

Enabling both networking and checkpointing for a vm universe job can cause networking problems when the job restarts, particularly if the job migrates to a different machine. condor_submit will normally reject such jobs. To enable both, then add the command

when_to_transfer_output = ON_EXIT_OR_EVICT

Take care with respect to the use of network connections within the virtual machine and their interaction with checkpoints. Open network connections at the time of the checkpoint will likely be lost when the checkpoint is subsequently used to resume execution of the virtual machine. This occurs whether or not the execution resumes on the same machine or a different one within the HTCondor pool.

Disk Images

Xen and KVM

While the following web page contains instructions specific to Fedora on how to create a virtual guest image, it should provide a good starting point for other platforms as well.

http://fedoraproject.org/wiki/Virtualization_Quick_Start

Job Completion in the vm Universe

Job completion for a vm universe job occurs when the virtual machine is shut down, and HTCondor notices (as the result of a periodic check on the state of the virtual machine). This is different from jobs executed under the environment of other universes.

Shut down of a virtual machine occurs from within the virtual machine environment. A script, executed with the proper authorization level, is the likely source of the shut down commands.

Under a Windows 2000, Windows XP, or Vista virtual machine, an administrator issues the command

> shutdown -s -t 01

Under a Linux virtual machine, the root user executes

$ /sbin/poweroff

The command /sbin/halt will not completely shut down some Linux distributions, and instead causes the job to hang.

Since the successful completion of the vm universe job requires the successful shut down of the virtual machine, it is good advice to try the shut down procedure outside of HTCondor, before a vm universe job is submitted.

Failures to Launch

It is not uncommon for a vm universe job to fail to launch because of a problem with the execute machine. In these cases, HTCondor will reschedule the job and note, in its user event log (if requested), the reason for the failure and that the job will be rescheduled. The reason is unlikely to be directly useful to you as an HTCondor user, but may help your HTCondor administrator understand the problem.

If the VM fails to launch for other reasons, the job will be placed on hold and the reason placed in the job ClassAd’s HoldReason attribute. The following table may help in understanding such reasons.

VMGAHP_ERR_JOBCLASSAD_NO_VM_MEMORY_PARAM

The attribute JobVMMemory was not set in the job ad sent to the VM GAHP. HTCondor will usually prevent you from submitting a VM universe job without JobVMMemory set. Examine your job and verify that JobVMMemory is set. If it is, please contact your administrator.

VMGAHP_ERR_JOBCLASSAD_KVM_NO_DISK_PARAM

The attribute VMPARAM_vm_Disk was not set in the job ad sent to the VM GAHP. HTCondor will usually set this attribute when you submit a valid KVM job (it is derived from vm_disk). Examine your job and verify that VMPARAM_vm_Disk is set. If it is, please contact your administrator.

VMGAHP_ERR_JOBCLASSAD_KVM_INVALID_DISK_PARAM

The attribute vm_disk was invalid. Please consult the manual, or the condor_submit man page, for information about the syntax of vm_disk. A syntactically correct value may be invalid if the on-disk permissions of a file specified in it do not match the requested permissions. Presently, files not transferred to the root of the working directory must be specified with full paths.

VMGAHP_ERR_JOBCLASSAD_KVM_MISMATCHED_CHECKPOINT

KVM jobs can not presently checkpoint if any of their disk files are not on a shared filesystem. Files on a shared filesystem must be specified in vm_disk with full paths.

VMGAHP_ERR_JOBCLASSAD_XEN_NO_KERNEL_PARAM

The attribute VMPARAM_Xen_Kernel was not set in the job ad sent to the VM GAHP. HTCondor will usually set this attribute when you submit a valid Xen job (it is derived from xen_kernel). Examine your job and verify that VMPARAM_Xen_Kernel is set. If it is, please contact your administrator.

VMGAHP_ERR_JOBCLASSAD_MISMATCHED_HARDWARE_VT

Don’t use ‘vmx’ as the name of your kernel image. Pick something else and change xen_kernel to match.

VMGAHP_ERR_JOBCLASSAD_XEN_KERNEL_NOT_FOUND

HTCondor could not read from the file specified by xen_kernel. Check the path and the file’s permissions. If it’s on a shared filesystem, you may need to alter your job’s requirements expression to ensure the filesystem’s availability.

VMGAHP_ERR_JOBCLASSAD_XEN_INITRD_NOT_FOUND

HTCondor could not read from the file specified by xen_initrd. Check the path and the file’s permissions. If it’s on a shared filesystem, you may need to alter your job’s requirements expression to ensure the filesystem’s availability.

VMGAHP_ERR_JOBCLASSAD_XEN_NO_ROOT_DEVICE_PARAM

The attribute VMPARAM_Xen_Root was not set in the job ad sent to the VM GAHP. HTCondor will usually set this attribute when you submit a valid Xen job (it is derived from xen_root). Examine your job and verify that VMPARAM_Xen_Root is set. If it is, please contact your administrator.

VMGAHP_ERR_JOBCLASSAD_XEN_NO_DISK_PARAM

The attribute VMPARAM_vm_Disk was not set in the job ad sent to the VM GAHP. HTCondor will usually set this attribute when you submit a valid Xen job (it is derived from vm_disk). Examine your job and verify that VMPARAM_vm_Disk is set. If it is, please contact your administrator.

VMGAHP_ERR_JOBCLASSAD_XEN_INVALID_DISK_PARAM

The attribute vm_disk was invalid. Please consult the manual, or the condor_submit man page, for information about the syntax of vm_disk. A syntactically correct value may be invalid if the on-disk permissions of a file specified in it do not match the requested permissions. Presently, files not transferred to the root of the working directory must be specified with full paths.

VMGAHP_ERR_JOBCLASSAD_XEN_MISMATCHED_CHECKPOINT

Xen jobs can not presently checkpoint if any of their disk files are not on a shared filesystem. Files on a shared filesystem must be specified in vm_disk with full paths.