Comment 0 for bug 1681531

When cloud-init configures networking, it uses `ifup`. However, after cloud-init is done, networking.service runs and attempts an `ifup -a --read-environment` it fails since the devices are already configured with a "RTNETLINK answers: File exists" (return code of 1).

The end result is that any service with a dependency of networking fails to start.

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From /var/log/cloud-init.log:

2017-04-10 17:36:11,608 - util.py[DEBUG]: Running command ['ip', 'link', 'set', 'ens3', 'down'] with allowed return codes [0] (shell=False, capture=True)
2017-04-10 17:36:11,615 - util.py[DEBUG]: Running command ['ip', 'link', 'set', 'ens3', 'name', 'eth0'] with allowed return codes [0] (shell=False, capture=True)
2017-04-10 17:36:11,635 - util.py[DEBUG]: Running command ['ip', 'link', 'set', 'ens4', 'name', 'eth1'] with allowed return codes [0] (shell=False, capture=True)
2017-04-10 17:36:11,651 - util.py[DEBUG]: Running command ['ip', 'link', 'set', 'eth0', 'up'] with allowed return codes [0] (shell=False, capture=True)
2017-04-10 17:36:11,654 - stages.py[INFO]: Applying network configuration from ds bringup=False: {'version': 1, 'config': [{'name': 'eth0', 'subnets': [{'address': '138.197.88.85', 'netmask': '255.255.240.0', 'gateway': '138.197.80.1', 'type': 'static', 'control': 'auto'}, {'address': '2604:A880:0800:0010:0000:0000:2ECE:D001/64', 'gateway': '2604:A880:0800:0010:0000:0000:0000:0001', 'type': 'static', 'control': 'auto'}, {'address': '10.17.0.10', 'netmask': '255.255.0.0', 'type': 'static', 'control': 'auto'}], 'mac_address': 'ee:90:f2:c6:dc:db', 'type': 'physical'}, {'name': 'eth1', 'subnets': [{'address': '10.132.92.131', 'netmask': '255.255.0.0', 'gateway': '10.132.0.1', 'type': 'static', 'control': 'auto'}], 'mac_address': '1a:b6:7c:24:5e:cd', 'type': 'physical'}, {'address': ['2001:4860:4860::8844', '2001:4860:4860::8888', '8.8.8.8'], 'type': 'nameserver'}]}
2017-04-10 17:36:11,668 - util.py[DEBUG]: Writing to /etc/network/interfaces.d/50-cloud-init.cfg - wb: [420] 868 bytes
2017-04-10 17:36:11,669 - main.py[DEBUG]: [local] Exiting. datasource DataSourceDigitalOcean not in local mode.
2017-04-10 17:36:11,674 - util.py[DEBUG]: Reading from /proc/uptime (quiet=False)

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From 'dmesg':
Apr 10 17:36:11 ubuntu systemd[1]: Started Initial cloud-init job (pre-networking).
Apr 10 17:36:12 ubuntu systemd[1]: Started LSB: AppArmor initialization.
Apr 10 17:36:12 ubuntu systemd[1]: Reached target Network (Pre).
Apr 10 17:36:12 ubuntu systemd[1]: Starting Raise network interfaces...
Apr 10 17:36:13 ubuntu ifup[1099]: Waiting for DAD... Done
Apr 10 17:36:13 ubuntu ifup[1099]: RTNETLINK answers: File exists
Apr 10 17:36:13 ubuntu ifup[1099]: Failed to bring up eth1.

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$ sudo journalctl -xe -u networking
Apr 10 17:36:12 ubuntu systemd[1]: Starting Raise network interfaces...
-- Subject: Unit networking.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit networking.service has begun starting up.
Apr 10 17:36:13 ubuntu ifup[1099]: Waiting for DAD... Done
Apr 10 17:36:13 ubuntu ifup[1099]: RTNETLINK answers: File exists
Apr 10 17:36:13 ubuntu ifup[1099]: Failed to bring up eth1.
Apr 10 17:36:13 ubuntu systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
Apr 10 17:36:13 ubuntu systemd[1]: Failed to start Raise network interfaces.
-- Subject: Unit networking.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit networking.service has failed.
--