is there a way to fallback on None Datasource None during ds-identify instead of disabling cloud-init

[grosbaloon]

Hello

when no data source is provided, is there a way to fallback on Datasource none during ds-identify instead of disabling cloud-init ?

Let me explain.

Download ubuntu cloud image and change root password (without using cloud init)

wget https://cloud-images.ubuntu.com/noble/current/noble-server-cloudimg-amd64.img
virt-customize -a noble-server-cloudimg-amd64.img --root-password password:pass

start image without data source :
qemu-system-x86_64 -m 2G -enable-kvm -cpu host -smp 4 -hda noble-server-cloudimg-amd64.img -netdev user,id=n1,hostfwd=tcp::60671-:22 -device virtio-net,netdev=n1,addr=03 -device e1000,netdev=n2,addr=04 -netdev user,id=n2 -device e1000,netdev=n3,addr=05 -netdev user,id=n3 -netdev user,id=n4 -net none -display none -nographic

ds-identify will not find any datasource and cloud init will be disabled
because of ds-identify default policy : search,found=all,maybe=none,notfound=disabled

root@ubuntu:~# cloud-id
disabled

I tried to change the policy to search,found=all,maybe=all,notfound=enabled in /etc/cloud/ds-identify.cfg
In that case, ds-identify will not find any datasource, cloud-init is enabled.
At runtime, cloud-init scan all possible datasources (takes a long time) and
finally fallback to datasource none.

root@ubuntu:~# cloud-id
none

and have the warning:

**************************************************************************
# A new feature in cloud-init identified possible datasources for        #
# this system as:                                                        #
#   []                                                                   #
# However, the datasource used was: None                                 #
#                                                                        #
# In the future, cloud-init will only attempt to use datasources that    #
# are identified or specifically configured.                             #
# For more information see                                               #
#   https://bugs.launchpad.net/bugs/1669675                              #
#                                                                        #
# If you are seeing this message, please file a bug against              #
# cloud-init at                                                          #
#    https://github.com/canonical/cloud-init/issues                      #
# Make sure to include the cloud provider your instance is               #
# running on.                                                            #
#                                                                        #
# After you have filed a bug, you can disable this warning by launching  #
# your instance with the cloud-config below, or putting that content     #
# into /etc/cloud/cloud.cfg.d/99-warnings.cfg                            #
#                                                                        #
# #cloud-config                                                          #
# warnings:                                                              #
#   dsid_missing_source: off                                             #
**************************************************************************

Is there any configuration option to fallback on datasource none during ds-identify instead ?

[holmanb]

Is there any configuration option to fallback on datasource none during ds-identify instead ?

It's in the docs. Look up datasource_list.

[CanReader]

datasource_list is the way, but there's a catch. ds-identify skips the whole search when the list has only one entry, or one entry plus None. So this gives you None right away with the default policy, no slow scan and no warning:

datasource_list: [ None ]

If you still want NoCloud when a seed is attached, use [ NoCloud, None ]. ds-identify passes both through without checking, and cloud-init falls back to None if there's no seed.

The catch is that ds-identify only reads it as a single line list like above. If you write it as a multi-line yaml list (- None) it ignores it, goes back to the default list and you get disabled again.

With your virt-customize setup:

virt-customize -a noble-server-cloudimg-amd64.img \
  --write /etc/cloud/cloud.cfg.d/99-datasource.cfg:'datasource_list: [ None ]'

You can put ds-identify.cfg back to the default policy too, you don't need notfound=enabled with this.

Ran ds-identify locally with both lists and the multi-line one to check this.