Comment 1 for bug 2067022

afaik this is not supported. You can turn this into a feature request on Discourse.

ATM you can only specify multiple interfaces at compose time like

maas admin vm-host compose 1389 cores=32 memory=65535 storage=default:512 architecture=amd64/generic interfaces='eth0:name=br_vlan_2,type=bridge;eth1:name=br_vlan_3,type=bridge' -k

However, you can achieve your goal using LXD directly. Just login to the LXD server and do something like

lxc config device add THE_LXD_VM_NAME eth1 nic network=br_vlan_2 name=eth1 nictype=bridged ..

(see https://discuss.linuxcontainers.org/t/how-to-add-a-network-interface-in-lxc/437)

and then report back the interface to maas.