VM host networking (deb/2.7/UI)

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In order to deploy a VM host in your MAAS network, you first need to set up a bridge to connect between your VM host and MAAS itself. This section explains several ways of accomplishing this.

Four questions you may have:

  1. How do I set up a VM host bridge with the web UI?
  2. How do I set up a VM host bridge with netplan?
  3. How do I set up a VM host bridge with libvirt?
  4. How do I set up SSH for use by libvirt?

To enable VM host networking features, MAAS must match the VM host IP address of a potential VM host with a known device (a machine or controller). For example, if a machine not known to MAAS is set up as a VM host, enhanced interface selection features will not be available.

It’s essential to enforce usage of IP addresses to avoid domain name conflicts, should different controllers resolve the same domain name with different IP addresses. You should also avoid using 127.0.0.1 when running multiple controllers, as it would confuse MAAS.

Set up VM host bridge with MAAS UI

You can use the MAAS UI to configure a bridge to connect a VM host to MAAS:

Select the machine you want to use as a VM host, switch to the “Network” tab. Select the network where you want to create the bridge and click “Create bridge:”

Configure the bridge on a subnet MAAS controls. You may use any IP mode for the bridge:

When you’re done, it should look something like this:

Then you can deploy Ubuntu.

Use netplan to configure a bridge

You can also use netplan to configure a VM host bridge:

Open your netplan configuration file. This should be in /etc/netplan. It could be called 50-cloud-init.yaml, netplan.yaml, or something else. Modify the file to add a bridge, using the example below to guide you:

network:
    bridges:
        br0:
            addresses:
            - 10.0.0.101/24
            gateway4: 10.0.0.1
            interfaces:
            - enp1s0
            macaddress: 52:54:00:39:9d:f9
            mtu: 1500
            nameservers:
                addresses:
                - 10.0.0.2
                search:
                - maas
            parameters:
                forward-delay: 15
                stp: false
    ethernets:
        enp1s0:
            match:
                macaddress: 52:54:00:39:9d:f9
            mtu: 1500
            set-name: enp1s0
        enp2s0:
            match:
                macaddress: 52:54:00:df:87:ac
            mtu: 1500
            set-name: enp2s0
        enp3s0:
            match:
                macaddress: 52:54:00:a7:ac:46
            mtu: 1500
            set-name: enp3s0
    version: 2

Apply the new configuration with netplan apply.

Use libvirt to configure a bridge

It is also possible to use libvirt to configure a virtual bridge. This method will also work for LXD VM hosts running on Ubuntu. Be aware that other methods may be required if you are configuring LXD on an OS other than Ubuntu.

By default, libvirt creates a virtual bridge, virbr0, through which VMs communicate with each other and the Internet. DHCP, supplied by libvirt, automatically assigns an IP address to each VM. However, to enable network booting in MAAS, you’ll need to provide DHCP in MAAS and either:

  1. Disable DHCP on libvirt’s default network, or
  2. Create a new libvirt network maas with DHCP disabled.

You can set up such a maas network like this:

cat << EOF > maas.xml
<network>
 <name>maas</name>
 <forward mode='nat'>
   <nat>
     <port start='1024' end='65535'/>
   </nat>
 </forward>
 <dns enable="no" />
 <bridge name='virbr1' stp='off' delay='0'/>
 <domain name='testnet'/>
 <ip address='172.16.99.1' netmask='255.255.255.0'>
 </ip>
</network>
EOF
virsh net-define maas.xml

Note that this network also has NAT port forwarding enabled to allow VMs to communicate with the Internet at large. Port forwarding is very useful in test environments.

Set up SSH

For MAAS to successfully communicate with libvirt on your VM host machine – whether you’re running from snap or package, or running rack controllers in LXD containers or on localhost – this example command must succeed from every rack controller:

virsh -c qemu+ssh://$USER@$VM_HOST_IP/system list --all

Here, $USER is a user on your VM host who is a member of the libvirtd Unix group on the VM host, and $VM_HOST_IP is the IP of your VM host. Note that insufficient permissions for $USER may cause the virsh command to fail with an error such as failed to connect to the hypervisor. Check the $USER group membership to make sure $USER is a member of the libvirtd group.

Set up SSH (libvirt only)

The maas user on your rack controllers will issue all libvirt commands. Therefore, you’ll need to set up SSH public keys on every rack controller for user maas. First create SSH keys on all rack controllers:

$ sudo -i
root@maas:~$ mkdir -p /var/snap/maas/current/root/.ssh
root@maas:~$ cd /var/snap/maas/current/root/.ssh
root@maas:~$ ssh-keygen -f id_rsa

Next, add the contents of ~maas/.ssh/id_rsa.pub to the VM host user’s ~$USER/.ssh/authorized_keys. To accomplish this, log into your VM host node, via SSH, from a host for which MAAS has a matching public SSH key.