cloud-init team mailing list archive

[Daniel Watkins <daniel.watkins@xxxxxxxxxxxxx>]

Hi Denis,

Thanks for using cloud-init, and for reaching out!

On Tue, May 12, 2020 at 10:06:25AM +0200, Denis Krienbühl wrote:
> Everything works great, and it seems as though cloud-init considers
> the config drive first. The logs tell me as much as cloud-init now
> uses the drive as a source, and not the metadata service.
> 
> I was wondering though, in what order does cloud-init consider
> sources? Say with cloud-init 19.2, Ubuntu 18.04, OpenStack.

The order in which datasources are considered is configurable.  You'll
want to look for datasource_list configuration setting in
/etc/cloud/cloud.cfg and /etc/cloud/cloud.cfg.d/* to discover if this is
configured on your system.  (On Ubuntu, you should see this configured
in /etc/cloud/cloud.cfg.d/90_dpkg.cfg, which is populated based on
debconf selections).

If no such configuration is present, then cloud-init will fall back to
using its builtin configuration:
https://github.com/canonical/cloud-init/blob/master/cloudinit/settings.py#L20-L59

In both the shipped Ubuntu config and the fallback config, ConfigDrive
is the second datasource that will be considered (before everything but
NoCloud).

> Everything works, but it would be nice to know if this is by accident
> or for good reason :-).

It's not by accident, certainly. :)  Generally, we prefer local data
sources over network data sources.  One example of why: datasources can
provide network configuration, which means we have a chicken/egg problem
with network data sources.  We (usually; this is datasource-specific
behaviour) have to bring up an ephemeral DHCP connection to fetch the
metadata, and mounting an ISO locally is more robust (and I would guess
quicker, though I have no data to back that up), so we'll do that
instead given the option.


Cheers,

Dan

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