resource/db_instance: set SourceRegion based on source_db ARN

[omeid]

As Per AmazonRDS/API/CreateDBInstanceReadReplica docs

	If you create an encrypted Read Replica in a different AWS Region,
	then you must specify a KMS key for the destination AWS Region.
	KMS encryption keys are specific to the AWS Region that they are
	created in, and you can't use encryption keys from one AWS Region
	in another AWS Region.

This commit sets the Read Replica Source Region based on the
replicate_source_db arn.

kms_key_id is managed as usual.
Fixes: #518
Related: #3337, #865

[omeid]

@catsby I believe you have done most of the db_instance read replica, so if you could review this, that would be excellent.

[omeid]

Requires aws/aws-sdk-go#1847 to land.

[jasdel]

The AWS SDK for Go's aws/aws-sdk-go#1847 PR has been replaced with aws/aws-sdk-go#2631 adding the outstanding unit tests and will be merged into master once reviewed.

[omeid]

aws/aws-sdk-go#2631 just landed, so this is good to go.

[omeid]

Any chance this could be merged in? maintaining a fork because of pending bug fixes is rather painful.

[bflad]

Hi @omeid 👋 Thank you for submitting this. For starters here, the maintainers will likely be looking for:

• Output showing that all existing replica acceptance testing is passing
• A covering acceptance test that fails before the change and passes after the change. There's a section in the Contribution Guide for how to add cross-region testing: https://github.com/terraform-providers/terraform-provider-aws/blob/master/.github/CONTRIBUTING.md#writing-and-running-cross-region-acceptance-tests

We will want to ensure that Terraform shows no difference if a replica_source_db ARN is provided and that no regressions are introduced with this change. Please reach out if you have any questions or do not have time to implement the testing.

[bflad]

This check would be safer and easier to understand using the AWS Go SDK provided ARN handlers arn.IsARN() and arn.Parse(), e.g.

		if arn.IsARN(v.(string)) {
			replicaSourceDbArn, err := arn.Parse(v.(string))
			if err != nil {
				return fmt.Errorf("error parsing replica_source_db as ARN: %s", err)
			}
			opts.SourceRegion = aws.String(replicaSourceDbArn.Region)
		}

[omeid]

Okay, I can make that change. Just shows how long this pr has been sitting here. (;

[bflad]

Hi again 👋 Since we haven't heard back, we are going to close this pull request for now. If anyone is still interested in this change, please submit a new pull request and we will take a fresh look. Thanks.

[omeid]

I am still interested in fixing this. However, since we have been waiting for this for almost two years before we heard anything from Terrraform, we can't prioritize putting time into this.

Also, I personally find it a bit distasteful that you leave a contributor waiting for an answer for two years but then promptly close the issue once you don't get a reply in a month or so over holiday season.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!