Deployer should be able to sync changes to the environment

[Kapil Thangavelu]

ie. version deployer config, sync changes from config to environment.

[Kapil Thangavelu (hazmat)]

This requires a bit of rearchitecture and dropping some dead weight in the form of pyjuju support ideally.

[Tom Haddon (mthaddon)]

This is definitely something that would be really nice to do. However, there are some cases when we wouldn't want to do this. For instance, in Mojo we often have one deployment config that deploys the services with all the options and one deployment config that has the relations, but doesn't specify any options.

We're doing this to avoid having to duplicate content in the two deployment phases, and of course you could do this perhaps differently with inheritance, but another case is where we want to add, for instance, landscape and ksplice subordinates to the environment. We want to be able to do that in a separate juju-deployer file, but then if we needed to run the deployer files that didn't include landscape and ksplice we wouldn't want them removed from the environment necessarily.

[Robert Bruce Park (robru)]

+1 for this, I'm often bitten by adding new options to my charms, and then adding the options to the services file, and then doing a mojo run and not having the options set based on what's in the services file because the service is already deployed. very annoying, and seemingly requires duplicating the information in the services file with a separate script that manually sets the options I want.

[Xavier Esteve (xesteve)]

We also need these feature to update the environment directly from the juju bundle and mojo, without using juju config.
We've been trying this function an it only executes the change when a new unit is added. If we decrease the number of units or change a config the "mojo deploy-diff" reflects the change but "mojo run" does nothing.

[Alvaro Uria (aluria)]

In mojo, comment #4 is achieved by using "apply-config-changes=True" as part of the deploy phase definition (more info: https://mojo.canonical.com/readme.html)