add feature for region self to use ec2metadata service for configuration

[trjstewart]

Proposed changes

implements solution for issue #26 - use aws ec2 metadata for region config

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
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[trjstewart]

I am currently unsure how I can add tests to cover the feature given the reliance on the ec2metadata service, open to suggestions.

[pleshakov]

@trjstewart thanks for the PR!

Please see a couple of consistency suggestions.

Additionally,
From the corresponding issue

I considered removing the region configuration all together and only using the EC2 Metadata service for configuration but I definitely think there is a use-case to allow for cross-region upstreams.

It is better to leave the region field so that we retain backward compatibility. I think the suggested special value self works OK. Alternatively, we could make the region field optional, so that if it is not set, then the asg-sync will try to discover the region.

We're gonna do some additional testing and get back to you shortly.

[trjstewart]

It is better to leave the region field so that we retain backward compatibility. I think the suggested special value self works OK. Alternatively, we could make the region field optional, so that if it is not set, then the asg-sync will try to discover the region.

A colleague of mine did actually raise this same question. Personally I am more a fan of declarative configuration rather than something that could be attributed to a typo or the like.

[pleshakov]

👍