aws.GetPrivateIPsForScalingGroup: Only return InService instances

[HeyBillFinn]

Proposed changes

Proposed fix for race condition described in #37.

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
  I tested this change locally, but I didn't add any automated tests.
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
  I didn't update any documentation, and I wonder if this should just be the default behavior (rather than providing a config option). If so, should we bump this to 1.5.0 in case it's a breaking change for current users?
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[pleshakov]

@HeyBillFinn thanks for the PR! we'll review and get back to you shortly

[pleshakov]

Hi @HeyBillFinn

Sorry for the delay!

The PR works well.

However, I would like to extend this feature as described below:

Rather than changing the existing behavior, add a new option for nginx-ags-sync to filter out instances of an auto scaling group that are not in the InService state.

To accomplish that, we introduce a new field as part of the upstream:

upstreams:
  - name: backend1
    autoscaling_group: asg-sync-4-WebserverGroup1-BTY7BPLKYTCW
    port: 80
    kind: http
    in_service: true # use instances that are in InService state only. Default is false.

By default, the in_service is false. This would preserve the existing behavior.

I wonder what you think about it?

Thanks for your proposal and this PR. However, I think it makes sense for us to continue with the implementation of this feature. We'll add the new YAML field, add any necessary tests and documentation.

Since your PR solves the problem, could you use it in the meantime? Meanwhile, we'll start working on the feature. Once we finish it, we'll publish a new 0.5-1 release. We'll make sure to mention you in the changelog.