VM host networking (snap/2.7/CLI)

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 MAAS CLI/API?
  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 when running multiple controllers, as it would confuse MAAS.

Use the MAAS API to configure a bridge

You can also use the MAAS CLI/API to configure a VM host bridge, with the following procedure:

  1. Select the interface you wish to configure the bridge on. This example uses the boot interface, since the boot interface must be connected to a MAAS controlled network – but any interface is allowed:

     INTERFACE_ID=$(maas $PROFILE machine read $SYSTEM_ID | jq .boot_interface.id)
  2. Create the bridge:

      BRIDGE_ID=$(maas $PROFILE interfaces create-bridge $SYSTEM_ID name=br0 parent=$INTERFACE_ID | jq .id)
  3. Select the subnet where you want the bridge (this should be a MAAS controlled subnet):

     SUBNET_ID=$(maas $PROFILE subnets read | jq -r '.[] | select(.cidr == "" and .managed == true).id')
  4. Connect the bridge to the subnet:

       maas $PROFILE interface link-subnet $SYSTEM_ID $BRIDGE_ID subnet=$SUBNET_ID mode="STATIC" ip_address=""

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:

            - enp1s0
            macaddress: 52:54:00:39:9d:f9
            mtu: 1500
                - maas
                forward-delay: 15
                stp: false
                macaddress: 52:54:00:39:9d:f9
            mtu: 1500
            set-name: enp1s0
                macaddress: 52:54:00:df:87:ac
            mtu: 1500
            set-name: enp2s0
                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
 <forward mode='nat'>
     <port start='1024' end='65535'/>
 <dns enable="no" />
 <bridge name='virbr1' stp='off' delay='0'/>
 <domain name='testnet'/>
 <ip address='' netmask=''>
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)

If you installed MAAS via snap, then create the needed SSH keys this way:

sudo mkdir -p /var/snap/maas/current/root/.ssh
cd /var/snap/maas/current/root/.ssh
sudo ssh-keygen -f id_rsa

Finally, you’ll need to add id_rsa.pub to the authorized_keys file in /home/<vm-host-user-homedir-name>/.ssh/, where <vm-host-user-homedir-name> is the name of your VM host user.