handling of series when resolving charm urls

[Francesco Banconi]

When deploying a charm without specifying a series and a revision, juju adds the model default series first and then uses the charm store for resolving the revision.
So for instance, having a bionic,xenial charm at revision 1 and then a bonic only one at revision 2 results in revision 1 to be deployed on 2.4.1 by default, which can be surprising, as not specifying the series is often intended as "just give me latest stable, I don't care about the series".
So, what would you think of changing the url resolving logic so that the model's default-series is only used for disambiguation, when the latest stable supports multiple series?

[Eric Claude Jones (ecjones)]

Hey Francesco,

How are you? Has there been any agreement as to what the default behavior should be? If I understand correctly you are suggesting that the latest revision's series take precedence over the model's default series.

[Richard Harding (rharding)]

Yes, I think that this is true. If the series isn't specified by the
operator at deploy time, and the charm prefers something else, I think
going with the charm author is suggesting is a safe bet. Since there's no
method for a model to not have a default series, it's basically always
overriding what the charm author suggests and so there's no method to rely
on the charm's preference.

On Mon, Nov 26, 2018 at 9:56 AM Eric Claude Jones <
<email address hidden>> wrote:

> Hey Francesco,
>
> How are you? Has there been any agreement as to what the default
> behavior should be? If I understand correctly you are suggesting that
> the latest revision's series take precedence over the model's default
> series.
>
> --
> You received this bug notification because you are a bug assignee.
> https://bugs.launchpad.net/bugs/1788604
>
> Title:
> handling of series when resolving charm urls
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/juju/+bug/1788604/+subscriptions
>

[Eric Claude Jones (ecjones)]

Hey Francesco,

While implementing your requested solution is fairly simple, I'd like to test the case you mention specifically. To do that I would need a charm that drops support for a series. Do you know of a charm that drops support for a series from one revision to the next or do you have reproduction steps for your case?

I am also assuming that in your hypothetical example above the model's default-series is set to 'xenial'. Is that assumption correct?

[Francesco Banconi (frankban)]

Hey Eric,

the jujushell charm did that:

(dev) ~ % charm show '~juju-gui/jujushell'
allow shell access to one's juju model through a web interface

Name jujushell
Owner juju-gui
Revision 15
Supported Series bionic
Tags ops
Subordinate false
Promulgated false
Home page https://github.com/juju/jujushell-charm
Bugs url https://github.com/juju/jujushell-charm/issues
Read juju-gui, everyone
Write juju-gui

CHANNEL CURRENT
stable true

(dev) ~ % charm show '~juju-gui/jujushell-14'
allow shell access to one's juju model through a web interface

Name jujushell
Owner juju-gui
Revision 14
Supported Series bionic, xenial
Tags ops
Subordinate false
Promulgated false
Home page https://github.com/juju/jujushell-charm
Bugs url https://github.com/juju/jujushell-charm/issues
Read juju-gui, everyone
Write juju-gui

CHANNEL CURRENT
stable true

And yes I the default-series was xenial.

[Eric Claude Jones (ecjones)]

https://github.com/juju/juju/pull/9519