Controlling ipv6 support per environment has become cumbersome

[ctheune]

With the new requirements to explicitly state whether IPv6/IPv4 is expected for a specific address we now need to introduce a lot of writing work to toggle this per environment (specifically when using dev containers which do not support IPv6 at all).

Need to review some deployments (e.g. directory and ask appops) to see what the writing looks like and how to provide a better toggle (on environment-basis?) to avoid if cascades both in the component code and potentially as well in the template code.

[ctheune]

I thought an improvement would be to provide multiple factories (like Address4, Address6, Address46) that are more explicit and can be used in settings like Attribute(Address4, ConfigString("{{host.fqdn}}")).

This is an improvement. However, this ticket is also about the issue that we need some flexibility whether a certain protocol may be optional in some environments (like v6 is required in production but optional or even not used in containers).

[ctheune]

I think the factory idea is interesting, but I'm not adding them right away as I think it's wrong WRT to the whole signalling whether v6 is wanted or optional.

We might also want to change the resolution into something more lazy (but happens during configuration in any case, we might need to explicitly trigger all unresolved attributes when configuration finishes to make sure they don't pop up during deployment) so that we can rely on a single factory.

Laziness would allow us to also consider things from the environment (like making a general marker that this environment only supports v4 or v6 or both and make it optional or required if nothing else is required on a specific address. specific addresses then should use something like v4='required', v4='optional', v4=False, etc.

This could then be placed on an environment attribute, too:

[environment]
address-v4-default = required
address-v6-default = optional
; address-v6-default = unused

[ctheune]

add migration info about how to restore old behaviour