cloud-init fails for minimal images (can't find locale-gen)

I launched a xenial minimal cloud-image (20180321) via LXD:

$ lxc remote add minimal-ubuntu-daily https://cloud-images.ubuntu.com/minimal/daily --protocol simplestreams

$ lxc image list minimal-ubuntu-daily
+-------+--------------+--------+---------------------------------------------+--------+---------+-------------------------------+
| ALIAS | FINGERPRINT | PUBLIC | DESCRIPTION | ARCH | SIZE | UPLOAD DATE |
+-------+--------------+--------+---------------------------------------------+--------+---------+-------------------------------+
| | 4278883fd349 | yes | ubuntu 16.04 LTS amd64 (daily) (20180321) | x86_64 | 92.16MB | Mar 21, 2018 at 12:00am (UTC) |

$ lxc launch minimal-ubuntu-daily:4278883fd349 x-min

Failure is:

2018-03-26 18:34:13,191 - stages.py[DEBUG]: Running module locale (<module 'cloudinit.config.cc_locale' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_locale.py'>) with frequency once-per-instance
2018-03-26 18:34:13,191 - handlers.py[DEBUG]: start: modules-config/config-locale: running config-locale with frequency once-per-instance
2018-03-26 18:34:13,191 - util.py[DEBUG]: Writing to /var/lib/cloud/instances/x-min/sem/config_locale - wb: [644] 24 bytes
2018-03-26 18:34:13,192 - helpers.py[DEBUG]: Running config-locale using lock (<FileLock using file '/var/lib/cloud/instances/x-min/sem/config_locale'>)
2018-03-26 18:34:13,192 - cc_locale.py[DEBUG]: Setting locale to en_US.UTF-8
2018-03-26 18:34:13,192 - debian.py[DEBUG]: Generating locales for en_US.UTF-8
2018-03-26 18:34:13,192 - util.py[DEBUG]: Running command ['locale-gen', 'en_US.UTF-8'] with allowed return codes [0] (shell=False, capture=False)
2018-03-26 18:34:13,194 - handlers.py[DEBUG]: finish: modules-config/config-locale: FAIL: running config-locale with frequency once-per-instance
2018-03-26 18:34:13,194 - util.py[WARNING]: Running module locale (<module 'cloudinit.config.cc_locale' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_locale.py'>) failed
2018-03-26 18:34:13,194 - util.py[DEBUG]: Running module locale (<module 'cloudinit.config.cc_locale' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_locale.py'>) failed
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 1871, in subp
    env=env, shell=shell)
  File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'locale-gen'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/cloudinit/stages.py", line 793, in _run_modules
    freq=freq)
  File "/usr/lib/python3/dist-packages/cloudinit/cloud.py", line 54, in run
    return self._runners.run(name, functor, args, freq, clear_on_fail)
  File "/usr/lib/python3/dist-packages/cloudinit/helpers.py", line 187, in run
    results = functor(*args)
  File "/usr/lib/python3/dist-packages/cloudinit/config/cc_locale.py", line 45, in handle
    cloud.distro.apply_locale(locale, locale_cfgfile)
  File "/usr/lib/python3/dist-packages/cloudinit/distros/debian.py", line 97, in apply_locale
    regenerate_locale(locale, out_fn, keyname=keyname)
  File "/usr/lib/python3/dist-packages/cloudinit/distros/debian.py", line 299, in regenerate_locale
    util.subp(['locale-gen', locale], capture=False)
  File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 1877, in subp
    stderr="-" if decode else b"-")
cloudinit.util.ProcessExecutionError: Unexpected error while running command.
Command: ['locale-gen', 'en_US.UTF-8']
Exit code: -
Reason: [Errno 2] No such file or directory: 'locale-gen'
Stdout: -
Stderr: -

This bug was fixed in the package livecd-rootfs - 2.515

---------------
livecd-rootfs (2.515) bionic; urgency=medium

  * Set the default locale to C.UTF-8 in all server and cloud images.
   (LP: #1751051, #1759003)

 -- Michael Hudson-Doyle <email address hidden> Tue, 27 Mar 2018 09:59:02 +1300

mwhudson, if you're bringing this back to xenial could you ensure this affects ubuntu-cpc/minimized only but not the rest of ubuntu-cpc? We'd like that as a first pass.

I wasn't planning on doing the xenial back port myself, but I can if you want...

A back-port that affects ubuntu-cpc:minimized (but not non-minimized) would be great because cloud-init does explode in the minimal images without the fix. We just don't want to see a change in the standard images.

> There is no regression as this change is scoped to ubuntu-cpc minimal images only, which have not been announced.

This sounds reasonable, but please could you check during SRU verification that the change has correctly affected this subset of images only? It seems to be that the largest risk here is that the change ends up being wider than intended by accident.

Hello Robert, or anyone else affected,

Accepted livecd-rootfs into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/livecd-rootfs/2.408.30 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

I'm going to perform verification of this now.

I have just performed two livefs builds using the proposed version (i.e. 2.408.30), one with the minimized subproject and one without.

In the minimized image, /etc/default/locale contains "LANG=C.UTF-8". In the non-minimized image, it contains "# File generated by update-locale".

This looks as expected to me, but I'm performing a non-minimized build using the updates version (i.e. 2.408.29) to confirm that.

The -updates version produces the same content as the -proposed version for non-minimized builds.

This bug was fixed in the package livecd-rootfs - 2.408.30

---------------
livecd-rootfs (2.408.30) xenial; urgency=medium

  * Set the default locale to C.UTF-8 in minimized cloud images.
    (LP: #1759003)

 -- Robert C Jennings <email address hidden> Tue, 08 May 2018 11:32:29 -0500

The verification of the Stable Release Update for livecd-rootfs has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.