I guess it is not a bug but a thing that needs to be fixed.
LXD creates all the interfaces as the physical machine has whenever I create or deploy services or LXD containers when using MAAS. I thought it will only create the interfaces I specified with '--constraints spaces=' option but it does not. I think it should be able to create the interfaces that we only specified with constraints so that we can save the IP resources and not create unnecessary resource and configurations.
dpkg -l '*maas*' | cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-===============================-====================================-============-=================================================
ii maas 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all "Metal as a Service" is a physical cloud and IPAM
ii maas-cli 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS client and command-line interface
un maas-cluster-controller <none> <none> (no description available)
ii maas-common 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS server common files
ii maas-dhcp 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS DHCP server
ii maas-dns 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS DNS server
ii maas-proxy 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS Caching Proxy
ii maas-rack-controller 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all Rack Controller for MAAS
ii maas-region-api 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all Region controller API service for MAAS
ii maas-region-controller 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all Region Controller for MAAS
un maas-region-controller-min <none> <none> (no description available)
un python-django-maas <none> <none> (no description available)
un python-maas-client <none> <none> (no description available)
un python-maas-provisioningserver <none> <none> (no description available)
ii python3-django-maas 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS server Django web framework (Python 3)
ii python3-maas-client 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS python API client (Python 3)
ii python3-maas-provisioningserver 2.0.0~beta5+bzr5026-0ubuntu1~xenial1 all MAAS server provisioning libraries (Python 3)
dpkg -l '*juju*' | cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============-================================-============-============================================
ii juju 2.0-beta7-0ubuntu1~16.04.2~juju1 all next generation service orchestration system
ii juju-2.0 2.0-beta7-0ubuntu1~16.04.2~juju1 amd64 Juju is devops distilled - client
un juju-core <none> <none> (no description available)
un juju2 <none> <none> (no description available)
juju add-machine --constraints spaces=mgmt,^public-api,^tunnel,^storage lxd:0
ubuntu@ac1:~$ sudo lxc list
+----------------------+---------+--------------------------------+------+------------+-----------+
| NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS |
+----------------------+---------+--------------------------------+------+------------+-----------+
| juju-machine-0-lxd-3 | RUNNING | 10.192.228.56 (eth0) | | PERSISTENT | 0 |
| | | 192.168.101.56 (eth1) | | | |
| | | 192.168.102.56 (eth2) | | | |
| | | 10.192.229.56 (eth3) | | | |
+----------------------+---------+--------------------------------+------+------------+-----------+
FWIW spaces constraints (or any other kind for that matter) do not apply to containers, only to machines. The `juju deploy --bind` command is meant to be the way to specify required connectivity (e.g. --bind '<name>=<space> ...') and thus imply the minimum number of NICs needed. However, --bind does not (yet) work like that for containers.