cloud-init crashes with IPv6 routes

[Michael Camilli]

I have static routes specified for two networks, and during cloud-init an error occurs as it tries to make use of NETMASK1.

  # Network 2
  eth1:
    addresses: # List of IP[v4,v6] addresses to assign to this interface
      - 2001:db8:abcd:abce:fe::1000/96

    routes: # List of static routes for this interface
      - to: 2001:db8:abcd:abce:fe::0/96
        via: 2001:db8:abcd:bbce:fe::2

  # Network 3
  eth2:
    addresses: # List of IP[v4,v6] addresses to assign to this interface
      - 2001:db8:abcd:abcf:fe::1000/96

    routes: # List of static routes for this interface
      - to: 2001:db8:abcd:abcf:fe::0/96
        via: 2001:db8:abcd:bbcf:fe::2

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/cloudinit/cmd/main.py", line 761, in status_wrapper
    ret = functor(name, args)
  File "/usr/lib/python3.6/site-packages/cloudinit/cmd/main.py", line 433, in main_init
    init.apply_network_config(bring_up=bring_up_interfaces)
  File "/usr/lib/python3.6/site-packages/cloudinit/stages.py", line 926, in apply_network_config
    netcfg, bring_up=bring_up
  File "/usr/lib/python3.6/site-packages/cloudinit/distros/__init__.py", line 233, in apply_network_config
    self._write_network_state(network_state)
  File "/usr/lib/python3.6/site-packages/cloudinit/distros/__init__.py", line 129, in _write_network_state
    renderer.render_network_state(network_state)
  File "/usr/lib/python3.6/site-packages/cloudinit/net/sysconfig.py", line 1011, in render_network_state
    base_sysconf_dir, network_state, self.flavor, templates=templates
  File "/usr/lib/python3.6/site-packages/cloudinit/net/sysconfig.py", line 1002, in _render_sysconfig
    contents[cpath] = iface_cfg.routes.to_string(proto)
  File "/usr/lib/python3.6/site-packages/cloudinit/net/sysconfig.py", line 199, in to_string
    netmask_value = str(self._conf["NETMASK" + index])
KeyError: 'NETMASK1'

Additional Info:
1. Using KVM on a private server
2. See above configuration details that cause an issue. Note in the documentation I could only find an example of an ipv4 route, so maybe you could enhance the documentation with an example for ipv6 if possible.

[Chad Smith (chad.smith)]

Thanks for filing a bug and making cloud-init better and for the documentation request plug as well.
I'm adding a docs tag to the bug so it could be looked at from a documentation standpoint as well.

This bug looks conspicuously like the former bug https://bugs.launchpad.net/cloud-init/+bug/1958506 which was fixed in cloud-init version 22.2. If possible, would you be able to try reproducing this issue with a newer version of cloud-init?

You may be able to install cloud-init upstream's latest approved upstream release of 23.1 from our copr repo
https://copr.fedorainfracloud.org/coprs/g/cloud-init/el-testing/packages/

Once cloud-init is upgraded to 23.1 try running `sudo cloud-init clean --logs --reboot` to force cloud-init to try to reconfigure the system and network from scratch across reboot. If the KeyError still persists, then we know this is a new bug and not one formerly fixed.
I'm marking it 'incomplete' status above. Please set back to 'New' if you get a chance to confirm that latest cloud-init 23.1 still exhibits this issue.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/4094