2.2 bootstrap to subnet 1659640

[jameinel]

Description of change

This implements support for "subnet=" as a placement directive on AWS. This allows you to do "juju bootstrap --to subnet=A.B.C.D/24" and have Juju match that to a specific subnet to provision a machine in. It works for bootstrap, and I believe it will also work for any instance that you provision thereafter. Since Subnet in AWS also constrains you to an Availability Zone it also has that effect.

Note, this doesn't have Unit tests yet, as it was mostly meant as an exploration as to what was possible, and it turned out to be quite easy to just implement. I'd like to add tests before we would actually land this.

QA steps

Create a bunch of subnets in your AWS VPC. Bootstrap with

  juju bootstrap aws/REGION --config vpc-id=VPC --to subnet=SUBNET

You can use --debug to see some of the details about the selection process. Or just note in your EC2 dashboard what subnet the resulting instance ends up in.

SUBNET can be a Name, subnet-id, or CIDR.

I haven't tested exactly what happens with "juju deploy --to" or "juju add-unit --to", though both should use the same logic (and it essentially just piggybacks on all our existing code to handle AvailabilityZones.)

Documentation changes

This would affect what a user can specify during "juju bootstrap", and if we have explicit documentation about using Spaces in AWS, we should definitely include this information.

Bug reference

lp:#1659640

[jamesbeedy]

This is beautiful! Thanks!

[anastasiamac]

!!build!!!

[anastasiamac]

I am really weary of code changes that have no tests added/modified.

Code by itself LGTM.
@nskaggs Considering the complexities involved, would be nice to have a set of functional tests for this...

[jameinel]

This was mainly a prototype to have us discuss whether this is a route to go. We definitely will want direct unit tests for the parsing function and functional tests that we can use this feature in various clouds. (Ideally it would not be AWS specific, though it is today.)

[jameinel]

Refactored the code and added a bunch of unit tests.

[jameinel]

While I think the code is sane and reasonably tested, I think its a bit late to actually land in 2.1. So I'll target 2.2 for this.

[nskaggs]

2.1.1? I'm not inherently opposed if it bridges the gap, but it seems like it's specific to AWS?

[jameinel]

It is very specific to AWS, it will take work to implement it elsewhere, as GCE/Azure doesn't have space support, and the specific changes for MAAS are also probably going to need MAAS changes (we make a request by name-of-space, not look up the subnets ourselves).

[jameinel]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10336

[jameinel]

$$merge$$ there was a test that needed tweaking that I had missed.

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju