test(hotplug): fix race getting ipv6

[aciba90]

Proposed Commit Message

test(hotplug): fix race getting ipv6

Add retry logic for _get_ip_addr to properly get the ipv6 address.

The  output of `ip --brief addr` can show
ens6 UP 192.168.13.34/20 metric 200 fe80::8fd:afff:fea3:f4ad/64 instead of
ens6 UP 192.168.13.34/20 metric 200 2a05:d012:ea0:c500:1373:45f4:aa83:517c/128 fe80::8fd:afff:fea3:f4ad/64 if executed so early that the kernel didn't expose the wanted ipv6 address.

Additional Context

https://jenkins.canonical.com/server-team/view/cloud-init/job/cloud-init-integration-jammy-ec2/lastCompletedBuild/testReport/tests.integration_tests.modules/test_hotplug/test_multi_nic_hotplug_vpc/

...
            assert "routing-policy" in new_nic_cfg
>           assert [
                {"from": secondary_priv_ip4, "table": 101},
                {"from": secondary_priv_ip6, "table": 101},
            ] == new_nic_cfg["routing-policy"]
E           AssertionError: assert [{'from': '192.168.1.57', 'table': 101}, {'from': 'fe80::f5:aeff:fe8a:d7d', 'table': 101}] == [{'from': '192.168.1.57', 'table': 101}, {'from': '2600:1f16:7b9:e900:ab5a:a297:8501:714', 'table': 101}]
E             
E             At index 1 diff: {'from': 'fe80::f5:aeff:fe8a:d7d', 'table': 101} != {'from': '2600:1f16:7b9:e900:ab5a:a297:8501:714', 'table': 101}
E             
E             Full diff:
E               [
E                   {
E                       'from': '192.168.1.57',
E                       'table': 101,
E                   },
E                   {
E             -         'from': '2600:1f16:7b9:e900:ab5a:a297:8501:714',
E             +         'from': 'fe80::f5:aeff:fe8a:d7d',
E                       'table': 101,
E                   },
E               ]

Test Steps

#!/bin/bash
set -euxo pipefail

export CLOUD_INIT_PLATFORM=ec2
export CLOUD_INIT_OS_IMAGE=jammy

for i in $(seq 1 10); do
        tox -e integration-tests -- --pdb tests/integration_tests/modules/test_hotplug.py::test_multi_nic_hotplug_vpc
done

Checklist

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[a-dubs]

Looks great!

[holmanb]

@aciba90 Nice, thanks for fixing this!

A couple of minor questions, but this looks good to me!

1. I don't remember why we call the .launch() context manager twice, is that intentional?

2. We already have _wait_till_hotplug_complete(), and the purpose of this operation is to wait for hotplug to complete (the outcome of hotplug, if not necessarily the systemd service). Would the fix make more sense in that function maybe?

[aciba90]

Thanks for the reviews!

1. I don't remember why we call the `.launch()` context manager twice, is that intentional?

We need a second instance in the same subnet to test that connectivity works properly from there. It is explained in the test docstring.

2. We already have _wait_till_hotplug_complete(), and the purpose of this operation is to wait for hotplug to complete (the outcome of hotplug, if not necessarily the systemd service). Would the fix make more sense in that function maybe?

I do not think so, as if so, _wait_till_hotplug_complete would:

1. Grow a lot of logic, regarding NICs, interfaces state, etc, that IMO would make the function more complex.
2. While I also think that the fix (retry-logic) does not 100% belong to the current function, I think it fits more natural than in _wait_till_hotplug_complete.

Thoughts?

[github-actions]

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