This reduces how much cloud-init is explicitly involved in what "vendor-data"
could accomplish. The goal of vendor-data was to provide the vendor with a
channel to run arbitrary code that accomodate for their specific platform.
Much of those accomodations are currently being done in cloud-init.
However, this now moves some of those things to default "vendor-data", instead
of cloud-init proper.
Basically, now we have an 'sdc:vendor-data' key in the metadata.
If that does not exist, then cloud-init will use the default.
The default, provides a boothook. That boothook writes a file into
/var/lib/cloud/per-boot/ . That file will be both written on every boot
and then executed at rc.local time frame (by 'scripts-per-boot').
It will then execute /var/lib/cloud/instance/data/user-script
and /var/lib/cloud/instance/data/operator-script if they exist.
So, the things that cloud-init is now doing outside of the default vendor-data
that I would rather be done in vendor-data is:
* managing the population of instance/data/user-script and
instance/data/operator-script. These could very easily be done
from the boothook, but doing them in cloud-init removes the necessity
for having a 'mdata-get' command in the image (or some other way for
the boothook script to query the datasource).
* managing the LEGACY things.
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