Comment 6 for bug 1677710

It's hard to reproduce the same error condition, as this happened during the development of a new feature (deploying ubuntu-core via MAAS). The closest I could get to it after some help from Ryan Harper was to run ds-identify on a normally deployed MAAS node with the current cloud-init and the proposed one, and check the results in /run/cloud-init/cloud.cfg.

Besides that, I also configured MAAS to enable the <release>-proposed pocket and the nodes deployed just fine, and with the new cloud-init from proposed installed.

For Yakkety:

With the current cloud-init, where the problem appears:
 *** 0.7.9-48-g1c795b9-0ubuntu1~16.10.1 500
        500 http://br.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 Packages

# remove generated files
root@15-89:/run/cloud-init# rm cloud.cfg ds-identify.log

# cloud-init configuration, set via dpkg-reconfigure cloud-init and unchecking all items:
root@15-89:/run/cloud-init# cat /etc/cloud/cloud.cfg.d/90_dpkg.cfg
# to update this file, run dpkg-reconfigure cloud-init
datasource_list: [ ]

# maas datasource config file, written to by MAAS:
root@15-89:/run/cloud-init# cat /etc/cloud/cloud.cfg.d/90_dpkg_maas.cfg
# written by cloud-init debian package per preseed entries
# cloud-init/{maas-metadata-url,/maas-metadata-credentials}
datasource:
  MAAS: {consumer_key: xCkt8HsCeFKXBgm5SD, metadata_url: 'http://10.0.5.5:5240/MAAS/metadata/',
    token_key: 9pjmU6kjNAfdhe3xsJ, token_secret: kARCFjDaswVYDRLTSCTg9rrvXMjB7cGb}

# let's call ds-identify:
root@15-89:/run/cloud-init# unset DS_MAIN
root@15-89:/run/cloud-init# /usr/lib/cloud-init/ds-identify

# and we have no MAAS in cloud.cfg (somehow it thinks ec2 could be a candidate):
root@15-89:/run/cloud-init# cat cloud.cfg
datasource_list: [ Ec2, None ]
datasource: {Ec2: {strict_id: "warn"}}

# the ds-identify log file has
root@15-89:/run/cloud-init# cat ds-identify.log
(...)
DSLIST=MAAS ConfigDrive NoCloud AltCloud Azure Bigstep CloudSigma CloudStack DigitalOcean Ec2 OpenNebula OpenStack OVF SmartOS
(...)
is_container=false
ec2 platform is 'Unknown'.
check for 'Ec2' returned maybe
1 datasources returned maybe: Ec2
[up 10525.51s] returning 0

Now I install the package from proposed:
 *** 0.7.9-90-g61eb03fe-0ubuntu1~16.10.1 500
        500 http://br.archive.ubuntu.com/ubuntu yakkety-proposed/main amd64 Packages

And repeat the steps. This time I get:
root@15-89:/run/cloud-init# cat cloud.cfg
datasource_list: [ MAAS, None ]

And the ds-identify log has:
root@15-89:/run/cloud-init# cat ds-identify.log
(...)
DSLIST=MAAS ConfigDrive NoCloud AltCloud Azure Bigstep CloudSigma CloudStack DigitalOcean Ec2 GCE OpenNebula OpenStack OVF SmartOS
(...)
is_container=false
check for 'MAAS' returned found
ec2 platform is 'Unknown'.
check for 'Ec2' returned maybe
Found single datasource: MAAS
[up 10721.60s] returning 0