The implemented architecture fallback mechanism is not transparent to the user

[Heinrich Schuchardt]

On my SiFive Unmatched I have lxd 5.0.0-b0287c1 22933.

$ lxc launch images:ubuntu/22.04 ubuntu-container
Creating ubuntu-container
Error: Failed instance creation: Failed creating instance record: Requested architecture isn't supported by this host

$ snapcraft --use-lxd
Launching a container.
Build environment is in unknown state, cleaning first.
An error occurred with the instance when trying to launch with 'LXD': Failed creating instance record: Requested architecture isn't supported by this host.
Ensure that 'LXD' is setup correctly and try again.

[Heinrich Schuchardt (xypron)]

lxd git-0c77815 22946 (latest/edge) is also broken.

[Stéphane Graber (stgraber)]

This is normal behavior when no image can be found for the local architecture.

images: doesn't have any riscv64 images.
ubuntu: only has 21.10
ubuntu-daily: has 22.04

[Heinrich Schuchardt (xypron)]

It is not the download of the image that is failing:

$ lxc launch images:ubuntu/21.10 ubuntu-container
Creating ubuntu-container
Error: Failed instance creation: Failed creating instance record: Requested architecture isn't supported by this host

You get a different error if the image does not exist:
Error: Failed instance creation: Failed getting remote image info: Failed getting image: The requested image couldn't be found

[Stéphane Graber (stgraber)]

`images:` never had any riscv64 image. When that happens, the image selector downloads the closest image available which in this case is an amd64 image.

[Heinrich Schuchardt (xypron)]

When an architecture is specified the expected error is thrown:

lxc launch images:ubuntu/21.10/riscv64 ubuntu-container
Creating ubuntu-container
Error: Failed instance creation: Failed getting remote image info: Failed getting image: The requested image couldn't be found

But the following still needs to be addressed.

The implemented architecture fallback mechanism is not transparent to the user.
* lxc should notify the user.
* A fallback should only occur if the foreign architecture is supported.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Isaac True (itrue)]

+1 @xypron - it fallbacks to x86_64 and downloads the image if the riscv64 image is not found:

ubuntu@itrue-riscv64:~$ sudo lxc launch ubuntu:20.04 focal
Creating focal
Error: Failed instance creation: Failed creating instance record: Requested architecture isn't supported by this host
ubuntu@itrue-riscv64:~$ sudo lxc image list
+-------+--------------+--------+---------------------------------------------+--------------+-----------+----------+-----------------------------+
| ALIAS | FINGERPRINT | PUBLIC | DESCRIPTION | ARCHITECTURE | TYPE | SIZE | UPLOAD DATE |
+-------+--------------+--------+---------------------------------------------+--------------+-----------+----------+-----------------------------+
| | 4ca869945db4 | no | ubuntu 20.04 LTS amd64 (release) (20221018) | x86_64 | CONTAINER | 399.15MB | Nov 8, 2022 at 2:07pm (UTC) |
+-------+--------------+--------+---------------------------------------------+--------------+-----------+----------+-----------------------------+

Running "launch" first downloads the x86_64 image, then reports that it's not compatible.