Explicit image selection

[John Arbash Meinel]

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...
>> It is reasonable to say "Juju will not support this use case",
>> making it really hard to support it is roughly the same. I can
>> also agree with "don't make it too easy because the shotgun is
>> loaded". But finding a nice balance between "the defaults are
>> sane, but you can override them when you know what you are doing"
>> seems useful.
> 
> My perception is that it's not *that* difficult to describe your
> images in enough detail to satisfy juju's requirements; and
> moreover that once we switch over to oxygen/simplestreams across
> the board it'll be even simpler to do so. Is it really any harder
> than creating those images in the first place? Because *that*
> seemed like a hassle whenever I did it (distant past, can't really
> remember anything except the tedium).

It is a different set of knowledge to bring up an instance, configure
it a bit, and then bundle it into an AMI, vs the descriptions from
oxygen/simplestreams/cloud-data.

So while it is possible, it is a non-trivial step. But we can discuss
things more in Oakland, etc.

> 
>> Is your concern that if you just set "image-id" then deploy a
>> charm from a different series? I think there is a small hole in
>> Juju that the constraints for the bootstrap node end up as the
>> default constraints for the whole environment. With no good way
>> of splitting them apart.
> 
> It's a bit dirty, I agree, but we have env-set now, and so the
> cases in which default-series and constraints need to differ
> between the bootstrap node and future instances can be, I think,
> trivially addressed. Because we've always known that env-set was
> coming, it never seemed important enough to add complexity to
> bootstrap configuration to address those cases. Am I missing
> something?

As for my personal expectations, I would have probably said "juju
bootstrap --constraints" would be for the state server nodes, and then
you could 'juju env-set' to set the global value. (How do you unset a
value if you specified it to bootstrap?)

Certainly it feels like the state server is meta infrastructure, vs
the things that you deploy are your infrastructure. So the state
server seems more unrelated to how you would want the rest of the
environment. But we already have a way to specify the env for each
service, and we can live with the situation. I'm not sure how it fits
a user's mental model.

> 
> Cheers William
> 

John
=:->
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