What happened if compute node machine restarts?

asked 2014-11-03 10:44:11 -0600

minherz gravatar image

Hello, I wonder what is happening when a machine that runs computation node with active VMs is shutdown due hardware malfunction or power outage and after some time restarting and returns back? Does OpenStack somehow manage "to move" VMs that were configured to that node to run on another node? What happened to networking between VMs on other nodes trying to reach VMs that were running on the shutdown node?

Thank you

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answered 2014-11-03 17:35:51 -0600

updated 2014-11-03 17:48:38 -0600

You can use resume_guests_state_on_host_boot=true value on your nova.conf to force nova resume your VMs when the host machine becomes available after restarting.

But about the automatic VM migration: I think currently openstack has no mechanism to detect host failure and automatic migration of all running VMs to other healthy hosts. This is a point where third parties doing business(They provide HA mechanism to openstack for legacy and non-cloud ready applications(stateful apps)).

Live migration(with shared storage) is a good method for compute node maintenance with zero down time for all services(VMs) running on the compute server. But is not a way to provide service high availability and automatic fail-over in the case of host failure. To have succesful live migration, both source and destination hypervisors must be on running(healthy) state.

In general, OpenStack tries to target applications that support recovery and resiliency in the application itself. This is a new paradigm on the application development(Stateless cloud-ready application development).

(You can configure openstack to work with vmware vcenter to provide automatic VM recovery in the case of host failure. But this is propertary solution as I said before)

About the networking between VMs when migrated to other hosts due to live migration: if you setup and confgure your openstack networking service properly with right configuration values, no networking problems will be in the case of VM migration. But some limitation exists(e.g. your both compute nodes need to be in the same network/subnet)

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Asked: 2014-11-03 10:43:32 -0600

Seen: 1,583 times

Last updated: Nov 03 '14