juju deploy without constraints can render an unusable unit

[Felipe Reyes]

When deploying a new application without the correct constraints juju will end up deploying an application with bindings to a machine that won't have the necessary NICs. This was observed using juju 2.14 and openstack provider.

Test Case:

juju add-model test
juju add-space main 10.0.0.0/24
juju add-space external 10.10.0.0/24

# nagios-a will be allocated to a machine with a single NIC
juju deploy --bind 'main public=external' cs:nagios nagios-a

# nagios-b will be allocated to a machine with 2 NICs as requested by the constraint
juju deploy --bind 'main public=external' --constraints "spaces=main,external" cs:nagios nagios-b

Here it's the output of my terminal when testing this use case:
https://pastebin.ubuntu.com/p/ww6x5bwzWf/

The expected behavior is that juju errors out when it finds that bindings to spaces that the machine doesn't have a ethernet device on OR when --constraints is not passed use the spaces binded for the application.

[Juan M. Tirado (tiradojm)]

Juju deployments are optimistic by default. There are no plans to change that at this moment. I add this to the wishlist.

[John A Meinel (jameinel)]

We have always held the position that deploy with bindings should imply constraints on the machines for that application. If we are failing to pass those through, it should be considered a regression.

Presumably with 2.14 you mean 2.9.14, can you confirm if you see this behavior with 2.8?

[Felipe Reyes (freyes)]

On Tue, 2021-09-14 at 21:44 +0000, John A Meinel wrote:
> We have always held the position that deploy with bindings should
> imply
> constraints on the machines for that application. If we are failing
> to
> pass those through, it should be considered a regression.
>
> Presumably with 2.14 you mean 2.9.14, can you confirm if you see this
> behavior with 2.8?

yes, 2.9.14. I will try 2.8 and follow up.

[Felipe Reyes (freyes)]

On Tue, 2021-09-14 at 21:44 +0000, John A Meinel wrote:
> can you confirm if you see this behavior with 2.8?

When using 2.8.11 the behavior is the same ->
https://pastebin.ubuntu.com/p/djnv4FD55f/

[Joseph Phillips (manadart)]

This should sort it:
https://github.com/juju/juju/pull/13422