Designing Amulet for Juju 2.0

[marcoceppi]

With 2.0 coming around the corner we should also make Amulet a little more 2.0 friendly by releasing Amulet 2.0!

First off, this is a chance for us to address several flaws in Amulet's original design that have festered over the years. Also, this should be something that, while breaks amulet 1.x should not deprecate amulet 1.x right away. There are a lot of charms written to use amulet 1.x and we shouldn't mess with that support, but also gently nudge authors to move in an amulet 2.0 direction.

This issue is meant to be a blueprint for this work, comments and suggestions will be incorporated into this body and work split out into separate issues.

Deployment

Items to be considered for Deployment class

Rename to Model

Going forward, in a Juju 2.0 world, we no longer have Deployments or Environments, but a controller that we can create models for. The testing harness should create a model for tests to run against, so Deployment will instead be the representation of a Model.

juju-deployer deprecation

Juju 2.0 will support bundles natively, including support for paths as a valid charm url. Given this, deployer is no longer needed and Amulet should interact directly with Juju via it's API/CLI.

Language update

Several methods in Deployment don't align with Juju verbiage. These should be updated to better reflect actual commands in juju.

Deployment.add

This should become Model.deploy to align with juju

Missing features

There are A LOT of new features in 2.0 which need to be represented in Amulet, spaces, storage, budget, resources.

Resources

This is vital for amulet to be used in CI/CD pipeline for bundles and charms

UnitSentry & Talisman

Going forward an overhaul of Talisman and UnitSentry should take place. Over the years it's become prickly to update and interact with

UnitSentry

Code examples

from amulet import Model

m = Model()
m = Model().from_bundle()

m.add_unit(service, scale)
m.deploy(service, charm, scale=int, resources={})
m.destroy('service')
m.relate('service:rel', 'service:rel')

m.services['service']  # Service(list)
m.services['service'].destroy()
m.services['service'].add_unit()
m.services['service'].attach()
m.services['service'].leader  # Unit(dict)

m.services['service'][int]  # Unit(dict)
m.services['service'][int].run_action('action', params={})
m.services['service'][int].actions => list of actions/parameters
m.services['service'][int].list_actions()
m.services['service'][int].run('cmd')
m.services['service'][int].destroy()
m.services['service'][int].storage => list of storage

m.machines  # list
m.machines[int]  # Machine(dict)
m.machines[int].run()