When running as an instance with a config-drive attached, cirros first copies the full content of the config-drive to /run/cirros/datasource/raw before processing it's contents. Since the /run partition is limited to a size of 200k, this fills up the partition almost completely even in a minimal environment. As soon as there is a bit more data on the config-drive than usual, e.g. because there are multiple ssh keys in the metadata or an extended userdata section, parsing the config-drive will fail completely. In the console-log there will be some errors like
2018-12-11 11:17:44.637794 | controller | b"cirros-ds 'local' up at 13.40"
2018-12-11 11:17:44.637907 | controller | b'cp: write error: No space left on device'
2018-12-11 11:17:44.638006 | controller | b'cp: write error: No space left on device'
2018-12-11 11:17:44.638104 | controller | b'cp: write error: No space left on device'
2018-12-11 11:17:44.638201 | controller | b'cp: write error: No space left on device'
2018-12-11 11:17:44.638299 | controller | b'cp: write error: No space left on device'
2018-12-11 11:17:44.638396 | controller | b'cp: write error: No space left on device'
2018-12-11 11:17:44.638531 | controller | b'failed to copy results from configdrive to /run/cirros/datasource'
We should increase the available space on the /run tmpfs so that we are not that close to the limit. Maybe we can also avoid doing the initial copy of the config-drive.
"Since the /run partition is limited to a size of 200k, this fills up the partition almost completely even in a minimal environment."
How/where did you see that limit?
I think /run is just mounted via the etc/fstab entry:
tmpfs /run tmpfs rw,nosuid,