Expose Juju provider in an environment variable

[Alvaro Uria]

On the following link, there is a list of exposed environment variables by Juju:
https://github.com/juju/juju/blob/01b24551ecdf20921cf620b844ef6c2948fcc9f8/doc/charms-in-action.txt#L94

Could the type of Juju provider be exposed?

Samples:
JUJU_PROVIDER='maas'
JUJU_PROVIDER='lxd'
JUJU_PROVIDER='openstack'
etc.

Such variable would help decide if actions such as open-port/close-port would be needed or not, since they are treated in the same way across all supported providers but they may not be needed on some of them (ie. maas, lxd).

This is a different approach from a previous issue filed at:
https://bugs.launchpad.net/juju/+bug/1741028
https://bugs.launchpad.net/juju-core/+bug/1427770

If we are able to track the provider, we won't call "open-port" in the first place.

Thank you.

[Junien F (axino)]

I'd rather have the charms always open-port and Juju do the right thing.

[John A Meinel (jameinel)]

Charms with custom code per provider that aren't inherently provider specific (proxy for AWS services, etc), seems like a bad choice.

While it may help a particular case, it often will lead to brittle charms.

[Launchpad Janitor (janitor)]

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