Do we still need juju upgrade-charm --switch ... ?

[Marco Ceppi]

On Thu, Mar 10, 2016 at 10:28 PM Ian Booth <ian.booth at canonical.com> wrote:

> So we have a feature of upgrade-charm which allows you to crossgrade to a
> different charm than the one originally deployed.
>
> From the upgrade-charm help docs:
>
> The new charm's URL and revision are inferred as they would be when
> running a
> deploy command.
> Please note that --switch is dangerous, because juju only has limited
> information with which to determine compatibility; the operation will
> succeed,
> regardless of potential havoc.
>
> What is the use case for this functionality? I seemed to get the
> impression it
> was used mainly with local repos? But given local repos are going away in
> 2.0,
> do we still need it? And given the potential for users getting things
> wrong, do
> we even want to keep it regardless? Note also --switch is not allowed with
> --path which is how local charms are upgraded.
>

We use switch a lot, and customers use this as well. The primary use case
is "I have a bug in production charm that is not available upstream yet". I
expect future 2.0 uses to look like this:

charm pull <charm>
<hack on code>
juju upgrade-charm --switch ./<charm> <service>

Another example, esp because of how the charmstore is structured now

juju deploy trusty/wordpress
# hackity hack
juju deploy --switch cs:~marcoceppi/trusty/wordpress wordpress


>
> What would folks lose if --switch were to be dropped for 2.0? Any
> objections to
> doing this?


I object. Switch should be updated to support ./local/directory/charm
instead of local:

Marco
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