provider/aws: ASG Notifications Resource

[catsby]

Opening this as a proposal for a new top level resource, to implement #1419

Syntax:

resource "aws_autoscaling_group" "asg_example" {
  name = "asg_with_notifications"
  [...]
}

resource "aws_autoscaling_group" "asg_example_2" {
  name = "other_asg_with_notifications"
  [...]
}

resource "aws_sns_topic" "some_topic" {
  name = "some_topic_name"
}

resource "aws_autoscaling_notification" "example" {
  group_name     = [
    "${aws_autoscaling_group.asg_example.name}",
    "${aws_autoscaling_group.asg_example_2.name}",
  ]
  notifications  = [
    "autoscaling:EC2_INSTANCE_LAUNCH", 
    "autoscaling:EC2_INSTANCE_TERMINATE"
  ]
  topic_arn      = "${aws_sns_topic.some_topic.arn}"
}

Motivation(s):

ASGs can send notifications to SNS Topics as events occur (see Notification Types below). The API supports a 1-1 relationship per ASG and SNS Topic.

I'm proposing a new top level resource primarily to support modulaization, such that a module author can yield an ASG and a consumer can then add notifications as needed.

Relevant APIs:

• PutNotificationConfiguration
• Notification types
• NotificationConfiguration

TODO:

• implementation
• acceptance tests
• docs

Future:

The current proposal above only supports a 1-1 for ASG-Topic, but we could likely expand it to support multiple ASG names in the future, so that the same notification config is shared on multiple ASGs. A group_names attribute could be added, containing a list of ASG names to apply this configuration to.

[phinze]

LGTM - implement away! 🚀

[catsby]

Basic implementation is done -- need to update some things and make sure the _update test works and is meaningful, but wanted to push what I have

[stack72]

@catsby this looks good. I guess I didn't like the idea of separation before but now I see the separation looks good :)

[catsby]

Implemented, tested, documented. Please review and test out. Thanks!

[stack72]

@catsby nice work :) Hoping to see a release of this soon!

[phinze]

I feel like we have this code elsewhere, but I'm unable to find it at the moment. Seems like a thing we should promote somewhere shared if it's common enough.

[cbednarski]

Would be nice on schema.Set.toList() or similar but this one is AWS-specific.

[phinze]

One nit that can be easily addressed port-merge - LGTM!

[mzupan]

worked great 👍

Your example in the body of the PR is group_names = [] but the docs look ok

[cbednarski]

If I understand correctly this feature actually abstracts creating multiple AWS resources at the same time from the same configuration "template". We should note that here to make it clear that this does not map 1:1 to what you'd see the API.

[catsby]

It's tricky to describe what this creates... they are resources in a since, but you can't access them directly... anyway, your point is valid. I'll expand on that.

[cbednarski]

@catsby LGTM!

[catsby]

good catch @mzupan , I updated the comment, it's [] (multiple) not "" (single)

[ghost]

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