Set Azure to only update metadata on BOOT_NEW_INSTANCE (SC-386)

[TheRealFalcon]

Proposed Commit Message

Set Azure to only update metadata on BOOT_NEW_INSTANCE

In #834, we refactored the handling of events for fetching new metadata.
Previously, in Azure's __init__, the BOOT event was added to the
update_events, so it was assumed that Azure required the standard BOOT
behavior, which is to apply metadata twice every boot: once during
local-init, then again during standard init phase.
https://github.com/canonical/cloud-init/blob/21.2/cloudinit/sources/DataSourceAzure.py#L356

However, this line was effectively meaningless. After the metadata was
fetched in local-init, it was then pickled out to disk. Because
"update_events" was a class variable, the EventType.BOOT was not
persisted into the pickle. When the pickle was then unpickled in the
init phase, metadata did not get re-fetched because EventType.BOOT was
not present, so Azure is effectely only BOOT_NEW_INSTANCE.

Fetching metadata twice during boot causes some issue for
pre-provisioning on Azure because updating metadata during
re-provisioning will cause cloud-init to poll for reprovisiondata again
in DataSourceAzure, which will infinitely return 404(reprovisiondata
is deleted from IMDS after health signal was sent by cloud-init during
init-local). This makes cloud-init stuck in 'init'

Additional Context

Note that the default update events are defined in the base class, so Azure doesn't need a separate definition here.

Found by Azure during SRU testing.

Test Steps

Run the updated integration test.

Additionally, manually verified with:

DEB_BUILD_OPTIONS=nocheck packages/bddeb -d
scp cloud-init_all.deb <launched_azure_instance>:/tmp/cloud-init.deb
ssh ubuntu@<azure_instance>
sudo dpkg -i /tmp/cloud-init.deb
cloud-init clean --reboot --logs
ssh ubuntu@<azure_instance>

Examine /var/log/cloud-init.log and verify Applying network configuration appears exactly once, then later we see:

Event Denied: scopes=['network'] EventType=boot-legacy
No network config applied. Neither a new instance nor datasource network update allowed

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

[anhvoms]

LGTM

[TheRealFalcon]

@blackboxsw , if you approve, don't merge right away. Looking at an integration test issue.

[TheRealFalcon]

I removed the integration test update. It conflicts with what I've done in #1001 so any necessary changes will go there. I posted my manual test steps, and that should be sufficient here.

[blackboxsw]

generally looks good. Want some manual test time on this thought tomorrow. base class update events look good at just EventType.BOOT_NEW_INSTANCE.

[blackboxsw]

Manual testing upgrade clean and existing systems looking good and re-applying network only when expected on 21.3-11-g843eb94b-1~bddeb