When adding a machine, min_hwe_kernel is not saved

[Alberto Donato]

When manually adding a machine from the UI, the min_hwe_kernel parameter is not persisted, even when a value is set.

The value is passed to the backend but it's not persisted in the database

[Alberto Donato (ack)]

This also happens when creating a machine from the API

[Alberto Donato (ack)]

It turns out the reason is that when start_commissioning is called, it sets the min_hwe_kernel unconditionally to the default one (which was empty in my case).

This behavior was changed in 4c0cf27391954e93fbfffed4d4f9a22f85ae289d

[Alberto Donato (ack)]

Also see https://code.launchpad.net/~newell-jensen/maas/+git/maas/+merge/327404 for reasons behind the chnage

[Newell Jensen (newell-jensen)]

Bjorn also pointed out that in the API documentation for commissioning there is no mention of setting the min_hwe_kernel.

[Lee Trager (ltrager)]

After discussing this in the SU I went through the code and some old reviews. We were mistaken that you can define the min_hwe_kernel during commissioning. You can only set it when creating a new machine or updating its settings. The min_hwe_kernel value is set to the value of default_min_hwe_kernel whenever commissioning is started. Before [1] min_hwe_kernel was only set if it wasn't set to something before. After [1] it was always set to the value of default_min_hwe_kernel regardless if the user had previously defined something. This means as of today if a user defines a min_hwe_kernel when adding a new machine it is always overwritten by the default_min_hwe_kernel even if that means no min_hwe_kernel will be set.

I think the min_hwe_kernel should only be set to the default_min_hwe_kernel value if min_hwe_kernel isn't defined. Users may want to have different min_hwe_kernels per host and always setting it to the global value during commissioning prevents that. If no min_hwe_kernel is set on the node and one is set globally commissioning will still set the min_hwe_kernel to default_min_hwe_kernel.

Alternatively we could just remove the ability to set a min_hwe_kernel when creating a new machine on the API and UI because as this bug points out it does nothing as of today.

[1] https://code.launchpad.net/~newell-jensen/maas/+git/maas/+merge/327404

[Lee Trager (ltrager)]

@Andres I assigned this to you as what we do is a product decision. Feel free to assign it to me or back to Alberto once we come to a decision.