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How does live migration works , how it make seamless migration to another compute without data traffic loss ?

asked 2015-02-06 12:35:45 -0500

raviinroorkee.7 gravatar image

updated 2015-02-06 12:36:27 -0500

Hi ,

I was looking into code for live migration in ice-house release. As per my understanding during live migration , nova compute instruct to do plug vif on destination host in pre live migration and then it pause VM and stop VM in source host in live migration. After successful live migration , it does post live migration at destination host where it resume VM and boot it. Once done it unplug vif on source host and tear off network on source host. What i could not get it when VM is paused on source host , how traffic packet does not get lost ? Also there are calls to setup_network_on_host and network_migrate_instance_start/finish via nova-network api but could not get pointer , how does it setup network,when port change goes to neutron . As most of function above does not have calls implemented in neutron ?

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answered 2015-02-10 04:18:31 -0500

raviinroorkee.7 gravatar image

Hi , Thanks for your reply. I check that link it only talks about function flow , i also described. However here below i have logs of compute node when doing live_migration .

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*2015-02-09 17:38:23.186 9978 INFO nova.compute.manager [-] [instance: f859b75e-86af-4926-92a1-90e4ae301d36] VM Paused (Lifecycle Event) 2015-02-09 17:38:23.275 9978 INFO nova.compute.manager [-] [instance: f859b75e-86af-4926-92a1-90e4ae301d36] During sync_power_state the instance has a pending task (migrating). Skip. 2015-02-09 17:38:23.534 9978 DEBUG nova.virt.driver [-] Emitting event <lifecycleevent: 1423483703.53,="" f859b75e-86af-4926-92a1-90e4ae301d36="&gt;" stopped=""> emit_event /usr/lib/python2.7/dist-packages/nova/virt/driver.py:1208

2015-02-09 17:38:23.534 9978 INFO nova.compute.manager [-] [instance: f859b75e-86af-4926-92a1-90e4ae301d36] VM Stopped (Lifecycle Event) 2015-02-09 17:38:23.539 9978 INFO nova.compute.manager [-] [instance: f859b75e-86af-4926-92a1-90e4ae301d36] _post_live_migration() is started..

############################################################################################### In logs, it talks about VM pause and VM stop state before starting post live migration. where it resume VM on destination host. It makes me think about no packet loss when VM is paused on stop before post live migration.

Also do you find how setup_network_on_host and network_migrate_instance_start/finish via nova-network api works ?

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I am not sure how that will work with nova-network. Honestly, you'll probably need to walk the code if the link I posted doesn't answer your question.

SamYaple gravatar imageSamYaple ( 2015-02-10 07:09:23 -0500 )edit
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answered 2015-02-08 23:20:51 -0500

SamYaple gravatar image

updated 2015-02-08 23:21:12 -0500

Hello, you seem to be talking about regular migration, or "cold" migration. During live migration the instances never shutdown (though it is paused for a short amount of time).

I think you will get a better understanding of the migration workflow by looking at this link. It describes the process well.

http://bodenr.blogspot.com/2014/03/op...

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Asked: 2015-02-06 12:35:45 -0500

Seen: 1,933 times

Last updated: Feb 10 '15