Our maas lan can't access internet and have a internal apt-mirror site 192.168.3.6. I changed mirror set of maas server's snippets/maas_proxy file like:

d-i     mirror/country string manual
d-i     mirror/http/hostname string 192.168.3.6
d-i     mirror/http/directory string /ubuntu
d-i     mirror/http/proxy string

I deployed two maas node ok. Dashboard show the two node's state are ready. But node's cloud-init client changed the apt's sources.list like this:

## Note, this file is written by cloud-init on first boot of an instance
## modifications made here will not survive a re-bundle.
## if you wish to make changes you can:
## a.) add 'apt_preserve_sources_list: true' to /etc/cloud/cloud.cfg
##     or do the same in user-data
...
deb http://archive.ubuntu.com/ubuntu precise main
deb-src http://archive.ubuntu.com/ubuntu precise main
...

Directly use cobbler install node(without maas), the node apt's sources.list like:

...
deb http://192.168.3.6/ubuntu precise main
deb-src http://192.168.3.6/ubuntu precise main
...

My question is:

1. How to set user-data in maas? So that I can set cloud-init's mirror's url to 192.168.3.6 or prevent cloud-init to change mirror's url.
2. Maas node's file /home/ubuntu/.ssh/authorized_keys is empty. Is it caused by the mirror's setup?