[openstack-dev] [nova] Enabling VM post-copy live migration

Luis Tomas luis at cs.umu.se
Thu Mar 12 08:41:13 UTC 2015


As part of an European (FP7) project, named ORBIT 
(http://www.orbitproject.eu/), I'm working on including the possibility 
of live-migrating VMs in OpenStack in a post-copy mode.
This way of live-migrating VMs basically moves the computation right 
away to the destination and then the VM starts working from there, while 
still copying the memory from the source to the new location of the VM. 
That way the memory pages are only copied as if the VM modifies them, 
they are already in the destination host. This basically ensures that 
migrations finish regardless of what the VM is doing, i.e., even 
extremely memory intensive VMs. Therefore removing the problem of having 
VMs hanging on in migrating state forever (as discussed in previous 
mails, e.g., 

So far, I have included and tested this new functionality at the JUNO 
version, and the code modifications can be found in the github 
repository of the project (branch named "post-copy"):
     - https://github.com/orbitfp7/nova/tree/post-copy --> mainly 
enabling the possibility of using the libvirt post-copy flag (libvirt 
driver.py). Note post-copy migration is not using "tunneling" as LibVirt 
patch for that is not yet ready.
     - https://github.com/orbitfp7/python-novaclient/tree/post-copy --> 
adding the possibility of using the post-copy mode when triggering the 
migration: nova live-migration [--block-migrate] [--post-copy] VM_ID
     - https://github.com/orbitfp7/horizon/tree/post-copy --> include a 
checkbox in the live-migration panel to perform the migration in 
post-copy mode. (like the one for enabling block-migration)

To be able to live-migrate VMs in a post-copy way, I'm relying on some 
kernel+qemu+libvirt modifications, not yet merged upstream (but in their 
way to it), also available at the project github:
     - Kernel: https://lkml.org/lkml/2015/3/5/576
     - Qemu: https://github.com/orbitfp7/qemu/tree/wp3-postcopy
     - LibVirt: https://github.com/orbitfp7/libvirt/tree/wp3-postcopy

If this is a nice feature to have in future versions of OpenStack, I'm 
happy to adapt the code for the next release (the one after KILO). Any 
comments are really welcome.

Best regards,

Dr. Luis Tomás
Postdoctoral Researcher
Department of Computing Science
Umeå University
luis at cs.umu.se

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