A multi-network friendly Openstack VM image with netplugd

barakme
A while (long while. Sorry about that) ago, I posted about setting up a VM in an Openstack cloud so that it worked nicely with multiple networks. I also promised that I would explain how to automate this process.
So, in this post, I will explain how to create an Openstack VM image that will automatically set up networking for all of the Openstack networks that are connected to the VM.
The principles and techniques explained here should work similarly in other clouds that support multiple networks (like Amazon VPC)

TL;DR

  • Create a VM from your base image, with a single network. 
  • SSH into the instance and install netplugd.
  • Configure netplugd with an appropriate script, tweaked for your choice of Linux distribution.
  • Delete files that are not required, stop the instance and create a new image from the instance.
  • The new image will work correctly with all connected networks.

The Problem – VM Images with one configured NIC

As discussed in the previous post, setting up the networks in Neutron and starting a VM that is attached to them is not enough. The VM has to cooperate with the network setup, somehow. 
In many of the images provided by cloud vendors and Linux distributions, only one Network Interface Card – eth0 – is defined, so only the first network is available to the VM.
You can set up the other NICs using ssh (it network access is possible with only one NIC), or with a user-data script that runs during the VM start-up (I’m not a fan of this approach – more on that in a different post). But the best way (in my opinion, anyway) is by baking this behavior into your image.

The Solution – VM Images with NICs configured by netplugd

netplugd is “a daemon that notifies the status of one or more ethernet interfaces, calling an external script when something changes.” 
And that is exactly what we need. (Another option is ifupd). 

Let’s get to work.

Network Setup
I’ll be using the same network setup as in the previous post.
Base VM
Start by creating a VM that is attached to a single network, and attach a floating IP to the instance. The command line is similar to the ‘nova boot’ command from the previous post, you’ll just need to pass a single network ID instead of two. We’ll be using the same security group and key-pair as well.
And ssh into the instance:
ssh -i demo-keypair.pem ubuntu@<Floating-IP>
Now to setup netplugd:
sudo apt-get install netplug
sudo mv netplug /etc/netplug/netplug
sudo chmod +x /etc/netplug/netplug
You should read the netplug file. It is a straightforward script that detects network cards that are plugged in/out, and then edits the interfaces file accordingly.
Note: your choice of Linux distribution might keep the interfaces configuration in a different location or file format. Some tweaking of this file might be necessary. The script as provided works on Ubuntu 12.04. Feel free to send in a pull request if you want to add your configuration to the repo.
Now, let’s clean up the VM and close the session:
rm ~/.ssh/authorized_keys
exit
Power off the instance
nova stop demo-vm
Wait until the VM fully shuts down. It should look something like this:
nova list –name demo-vm
Create a snapshot of the image:
nova image-create demo-vm “Ubuntu 12.04 with netplugd”
 
We can now delete the VM
nova delete demo-vm
 
Your image is now ready!
Let’s  take it out for a spin. We’ll use both networks this time:
nova boot –flavor standard.medium –image “Ubuntu 12.04 with netplugd” –security-groups demo-security-group –key-name demo-keypair –nic net-id=XXXXX-XXXX-XXXX-XXXX-XXXXXXXX –nic net-id=YYYYYY-YYYY-YYYY-YYYY-YYYYYYYYYYYY demo-vm
 Attach a floating IP to the instance and ssh into it.
 ssh -i demo-keypair.pem ubuntu@<Floating-IP> ifconfig
 
 
Note how both NICs are up and running? You now have a multi-network friendly Openstack Image. Enjoy.

One last thing, and this one always gets first-time users.
Just cause the NICs are up, doesn’t mean all is well in networking land. You are probably going to need to set up routing rules to determine which NIC should be used for each of your network packets. These rules depend on what you are trying to accomplish in this network configuration. But we’ll leave that for another post. For now, consult with your sysadmin.

 

7 thoughts on “A multi-network friendly Openstack VM image with netplugd”

  1. Hi Barakme,

    There is one question is that can we just implement the netplug in base image?
    Why we need to create a new image by a VM which has been implemented by netplug?

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  2. As long as netplugd is in the image you use when the VM starts, it will work fine. Most base images people use are the ones provided by the linux distribution vendors. This is usually a good idea, as you get a safe, cloud-ready, linux distro. But they usually do not include netplugd, or something similar to it.

    So you usually have to create a new image from your preferred starting point.

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  4. Hi, thank you for sharing the knowledge. I am trying to find the interface names in Openstack instance, which is defined before by Neutron, i can attach multiple interfaces but i want to have these names(net_a, net_x..) instead of eth or ens. I assume Nova only transfers the MAC address of port to the virtual instance. So the instances get IPs but with that ‘eth’ ‘ens’ names.

    Have you seen that with netplugd, interface names will be same also, or is there a way to find Neutron specific custom interface names in machine?

    Thanks in advance

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    • As far as I know, Neutron does not specify interface names. I know that some cloud infrastructures allow for a recommended interface name, but the OS image has to cooperate and load this meta-data. And this is fairly rare. Usually, the interface name is set by the OS.

      The best way to do this is probably with a start-up script baked into the image or set in the user-data configuration of the image. Have that script set the interface names as you require them.

      If you find a better way of doing this, do post it here. It’s an interesting question.

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