How to manage VM hosts (deb/3.0/CLI)

2.9 3.0 3.1

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. Once that’s done, you can add and manage VM hosts – and subsequently, create VMs to act as MAAS machines. This article explains:

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.

How to 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
  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=""

How to set up a VM host bridge with netplan

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.

How to set up a VM host bridge with libvirt

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.

How to set up SSH for use by libvirt

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.

How to 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/ 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.

How to add a VM host

Upon selecting “Authenticate” (assuming successful authentication), you will receive a project selection screen similar to this:

You must either enter a new project name (which cannot contain spaces or special characters), or you must select an existing project. If you’re not really planning on using projects, selecting the “default” project will allow you to continue working as you have in the past.

To add a VM host:

maas $PROFILE vm-host create type=$VM_HOST_TYPE power_address=$POWER_ADDRESS \
    [power_user=$USERNAME] power_pass=$PASSWORD {project=$PROJECT} \
    [zone=$ZONE] [tags=$TAG1,$TAG2,...]

$VM_HOST_TYPE can currently take two values: virsh and lxd.

$POWER_ADDRESS typically looks like the following for libvirt:

qemu+ssh://<vm host IP>/system

of like this for LXD (Beta):

Both $USERNAME and $PASSWORD are optional for the virsh power type. $ZONE and $TAGS are optional for all VM hosts.

The power_... parameters will vary with power type. See the API reference for a listing of available power types.

For example, to create a LXD VM host, enter the following:

maas $PROFILE vm-hosts create type=lxd power_address=$LXD_BRIDGE_ADDRESS \
   power_pass=$LXD_TRUST_PASSWORD project=$PROJECT_NAME

Note that for LXD VM hosts, a project name is not optional. Project names cannot contain spaces or special characters. If you enter a project name which doesn’t exist, MAAS will create the LXD project for you.

MAAS will automatically discover and store the resources your VM host contains. Any existing machines will also appear on the ‘Machines’ page, and MAAS will automatically attempt to commission them.

How to configure a VM host

Using the CLI, it’s possible to update the configuration of a VM host. You can change these configurable parameters with an update command – but first, you’ll want to know how to check the values of configurable parameters, both before and after the change.

How to list VM-hosts

To begin, you can list your available KVM-hosts with the following command:

maas admin vm-hosts read | jq -r '(["ID, "VM-HOST","SYSID","CORES",
"USED","RAM", "USED","STORAGE", "USED"] | (., map(length*"-"))),
(.[]| [.id,.name,.host.system_id,.total.cores, .used.cores, .total.memory, .used.memory,.total.local_storage, .used.local_storage])
| @tsv' | column -t

How to list configurable VM host parameters

There are just a few parameters that you can change for a VM host. You can list these, on a per-host basis, using the following two-step procedure:

  1. Run the command above to get the VM host ID (different from the System ID, see the first column in the listing).

  2. Enter the following command to list configurable parameters:

maas admin vm-host read $ID | jq -r '(["ID","NAME","POOL","ZONE",
"CPU-O/C", "RAM-O/C", "TAGS"] | (., map(length*"-"))), (.| [.id,.name,,,.cpu_over_commit_ratio, 
.memory_over_commit_ratio, .tags[]]) | @tsv' | column -t

where $ID is the ID (not System ID) of the VM-host.

How to change a VM host’s name

You can change the VM host’s name very simply, with this command:

maas admin vm-host update $ID name=$NEW_NAME

where $ID is the VM host’s ID (not System ID), and $NEW_NAME is the new name you want to assign. You can check that the change was successful by just printing out the ID and name, like this:

maas admin vm-host read $ID | jq -r '(["ID","NAME"] 
| (., map(length*"-"))), (.| [.id,.name]) 
| @tsv' | column -t

How to change a VM host’s pool

You can also change the VM host’s pool with a simple command:

maas admin vm-host update $ID pool=$VALID_POOL

where $ID is the VM host’s ID (not System ID), and $VALID_POOL is the name of a pool that already exists. If you mention a pool you haven’t created yet, you’ll get an error like this:

{"pool": ["Select a valid choice. That choice is not one of the available choices."]}
maas admin resource-pools read | jq -r '.[] | (.name)'

If you really want to set your VM host to a new one, you just need to create a new one with this command:

maas admin resource-pools create name=$NEW_POOL_NAME

Then double-check it with catvmpools, and assign your VM host to it using the earlier command.

How to list the resources of all VM hosts

maas $PROFILE vm-hosts read

A portion of the sample output:

        "id": 93,
        "capabilities": [
        "name": "civil-hermit",

How to list the resources of a single VM host

To list an individual VM host’s resources:

maas $PROFILE vm-host read $VM_HOST_ID

How to update a VM host’s configuration

Update overcommit ratios for a KVM host:

maas $PROFILE vm-host update $VM_HOST_ID power_address=qemu+ssh://ubuntu@ \
        power_pass=example cpu_over_commit_ratio=2.5 memory_over_commit_ratio=10.0

Update the default storage pool used by a KVM host:

maas $PROFILE vm-host update $VM_HOST_ID power_address=qemu+ssh://ubuntu@ \
        power_pass=example default_storage_pool=pool2

How to list a VM host’s connection parameters

To list a VM host’s connection parameters:

maas $PROFILE vm-host parameters $VM_HOST_ID

Example output:

    "power_address": "",
    "power_pass": "admin",
    "power_user": "admin"