Fix stacktrace in DataSourceRbxCloud if no metadata disk is found.

[smoser]

Proposed Commit Message

Fix stacktrace in DataSourceRbxCloud if no metadata disk is found.

Largely speaking, ds-identify protects from this scenario being
hit, but if DataSourceRbxCloud ran and there was no metadata
disks found (LABEL=CLOUDMD), then it would stacktrace.

The fix is just to clean up the get_md function a little
bit, and the explicitly check for False as a return value in _get_data.

Additional Context

This was seen in a log attached to LP: #1901831.

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

[igalic]

🙋🏻‍♀️

[igalic]

instead of (or in addition to) this long-winded doc-string, we could add a type annotation

[OddBloke]

instead of (or in addition to) this long-winded doc-string, we could add a type annotation

The return type is Union[dict, bool] which we can't express in our still-supporting-3.4 codebase.

[TheRealFalcon]

Do you think it makes sense to have get_md return an empty dictionary rather than false if nothing is found and then in generate_network_config check if rbx_data is truthy? Either way, I think this looks good.

[OddBloke]

Thanks, Scott!

[OddBloke]

instead of (or in addition to) this long-winded doc-string, we could add a type annotation

The return type is Union[dict, bool] which we can't express in our still-supporting-3.4 codebase.

[mitechie]

@smoser we're looking at SRU verification for this, do you have access to test this or was this a side fix that is not easily verifiable?

Thanks

[smoser]

Recreating the failure can be done like:

# force-enable cloud-init with ds-identify.cfg and put RbxCloud in the search list before NoCloud
$ lxc init ubuntu-daily:bionic b1
$ echo "datasource_list: [ RbxCloud, NoCloud ]" | lxc file push - b1/etc/cloud/cloud.cfg.d/90_dpkg.cfg
$ echo policy: enabled | lxc file push - b1/etc/cloud/ds-identify.cfg

# start the system and wait till cloud-init is done.  cloud-init shoudl run to completion and find the
# lxc provided NoCloud
$ lxc start b1
$ lxc exec b1 -- cloud-init status --wait

# but, there will be a stack trace and warnings in the log from when RbxCloud did not find anything.
$ lxc exec b1 -- grep WARN /var/log/cloud-init.log
2020-12-10 00:31:50,348 - util.py[WARNING]: Failed to load metadata and userdata
2020-12-10 00:31:50,348 - util.py[WARNING]: Getting data from <class 'cloudinit.sources.DataSourceRbxCloud.DataSourceRbxCloud'> failed