Comment 7 for bug 1599886

cloud-init on trusty has no functionality for security repository. (0.7.5-0ubuntu1.21)

below commit on upstream is related but there are a lot of dependencies. so i'm not sure it's fixable.

commit d861415ff9ab816b1183b8c58ec35348be4fd458
Author: Christian Ehrhardt <email address hidden>
Date: Wed Aug 10 16:43:14 2016 +0200

    Apt: add new apt configuration format

    This adds an improved apt configuration format that is fully backwards
    compatible with previous behavior. This is mostly copied from curtin's
    implementation.

    It does:
     * clean up and centralizes many of the top level 'apt_*' values that
       previously existed into a single top level 'apt'key.
     * support a 'source' in apt/sources/entry that has only a key
     * documents new features and adds tests.

    See the added doc/examples/cloud-config-apt.txt for more information.