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How to configure VM to have only one network interface

asked 2013-12-24 18:19:50 -0500

amitg gravatar image

updated 2013-12-27 14:19:06 -0500

smaffulli gravatar image

I have setup Openstack using Centos 6.4 controller (havana, RDO) and 4 compute nodes (KVM) using nova-network. 2 compute nodes are in 10.77.1.0/24 and remaining 2 are in 10.77.2.0/24 networks. I have created 2 networks as well using "nova-manage network create". Network uses FlatManager and instances get IP from external DHCP. No firewall. eth0 is the interface on controller while compute nodes use br100 (bridged into eth0).

All compute nodes and instances are able to talk with each other however after adding the second network, I have started seeing following issue:

Issue: when I create instance from dashboard, they show 2 IPs on the dashboard. Instance created this way gets 2 eth devices also however only 1 is configured from my external DHCP server. I want to be able to create instance with just 1 network-interface. one that is connected and configured by external DHCP on the eth0 of compute host.

I have tried playing with nova aggregates, de-associate commands but am not able to set it right. Please help. I have 2 clusters and can try anything in my dev. env.

PS: Instances from CLI "nova boot --nic ..." command look fine and show only 1 IP assigned in dashboard.

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answered 2013-12-30 14:34:36 -0500

Cristi Falcas gravatar image

The second interface doesn't have an IP most probably because is not configured in the guest OS for this.

Are you using nova-network or neutron? For neutron I know that you can select the attached networks from the dashboard.

If you're using nova-network try to switch to ml2 and neutron.

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Thank you for your reply. I'm using nova-network. main motivation is multi_host design. I want to be able to create instance with just 1 network-interface. ie. I do not want 2 network interfaces on almost all my VMs.

amitg ( 2013-12-30 22:01:10 -0500 )edit

Do you have a Networking tab when you create a new instance (here you can select where to attach the VM). Something like this: http://www.sebastien-han.fr/images/horizon-instance-boot.jpg

Cristi Falcas ( 2013-12-31 02:10:22 -0500 )edit

I do not have network tab in dashboard. How do I get this tab? I guess if I got this tab and a way to bind associate a network to a host or host aggregate then it would work great!

amitg ( 2013-12-31 10:06:13 -0500 )edit

I think that it's only available when using neutron. It's not that hard to switch to neutron, especially if you use flatmanager. But I think that the existing network can't be easily migrated: you will have to destroy it and recreate all your VMs.

Cristi Falcas ( 2013-12-31 12:01:59 -0500 )edit

I agree - I guess I can't have network-tab in nova-network. Thank you for the confirmation. Please let me know if you have a reference doc for me that is close to: No firewall, no GRA no VLAN, multi_hpst=True or equiv., no teneant network, All physical provider network for VMs & external gateway, and no single point of failure (requirement of network-controller node doing all network IO for VMs)

amitg ( 2013-12-31 17:32:39 -0500 )edit
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answered 2014-01-01 20:11:20 -0500

amitg gravatar image

Thank you Cristi and all people who replied.

Another possible alternative/solution: I did 'nova network-delete' of all defined networks. creating VMs after that had no eth0 device so I modified compute/manager.py (functions: run_instance and rebuild) to include a small script that virsh-attaches eth0 device (to bridge into br100). This seems to have done the trick for me now! dashboard also looks good with no confusing IPs :)

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Actually this is not very good from my point of view. It should work without modufying any code.

Cristi Falcas ( 2014-01-01 20:51:37 -0500 )edit

I'm doing tests so see if there are any side effects. Code change is minimal and should not hinder upgrades in significant way but time will tell. At moment I have happy customers

amitg ( 2014-01-01 21:03:56 -0500 )edit

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Asked: 2013-12-24 18:19:50 -0500

Seen: 240 times

Last updated: Jan 01