Apt install of python-dnspython can fail and there are no retries. This leads to the python module being absent:
[log snippet]
2016-03-17 06:34:20 INFO juju-log cloud-compute:53: Installing python-dnspython with options: ['--option=Dpkg::Options::=--force-confold']
2016-03-17 06:34:20 INFO cloud-compute-relation-changed Reading package lists...
2016-03-17 06:34:22 INFO cloud-compute-relation-changed Building dependency tree...
2016-03-17 06:34:22 INFO cloud-compute-relation-changed Reading state information...
2016-03-17 06:34:23 INFO cloud-compute-relation-changed The following packages were automatically installed and are no longer required:
2016-03-17 06:34:23 INFO cloud-compute-relation-changed libfreetype6 os-prober
2016-03-17 06:34:23 INFO cloud-compute-relation-changed Use 'apt-get autoremove' to remove them.
2016-03-17 06:34:23 INFO cloud-compute-relation-changed The following NEW packages will be installed:
2016-03-17 06:34:23 INFO cloud-compute-relation-changed python-dnspython
2016-03-17 06:34:23 INFO cloud-compute-relation-changed 0 upgraded, 1 newly installed, 0 to remove and 11 not upgraded.
2016-03-17 06:34:23 INFO cloud-compute-relation-changed E: Could not open file /var/lib/apt/lists/security.ubuntu.com_ubuntu_dists_trusty-security_main_i18n_Translation-en - open (2: No such file or directory)
2016-03-17 06:34:24 INFO cloud-compute-relation-changed Traceback (most recent call last):
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/cloud-compute-relation-changed", line 1134, in <module>
2016-03-17 06:34:24 INFO cloud-compute-relation-changed main()
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/cloud-compute-relation-changed", line 1127, in main
2016-03-17 06:34:24 INFO cloud-compute-relation-changed hooks.execute(sys.argv)
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/charmhelpers/core/hookenv.py", line 717, in execute
2016-03-17 06:34:24 INFO cloud-compute-relation-changed self._hooks[hook_name]()
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/cloud-compute-relation-changed", line 654, in compute_changed
2016-03-17 06:34:24 INFO cloud-compute-relation-changed ssh_compute_add(key, rid=rid, unit=unit)
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/nova_cc_utils.py", line 852, in ssh_compute_add
2016-03-17 06:34:24 INFO cloud-compute-relation-changed hosts.append(get_host_ip(private_address))
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/charmhelpers/contrib/network/ip.py", line 417, in get_host_ip
2016-03-17 06:34:24 INFO cloud-compute-relation-changed ip_addr = ns_query(hostname)
2016-03-17 06:34:24 INFO cloud-compute-relation-changed File "/var/lib/juju/agents/unit-nova-cloud-controller-0/charm/hooks/charmhelpers/contrib/network/ip.py", line 394, in ns_query
2016-03-17 06:34:24 INFO cloud-compute-relation-changed import dns.resolver
2016-03-17 06:34:24 INFO cloud-compute-relation-changed ImportError: No module named dns.resolver
2016-03-17 06:34:24 ERROR juju.worker.uniter.operation runhook.go:107 hook "cloud-compute-relation-changed" failed: exit status 1
