Add AWS_INSTANCE_IPV6 support to the AWS-SD provider

[mjlshen]

Description
As reported in the issue, the AWS-SD provider did not support the AWS_INSTANCE_IPV6 attribute type: https://docs.aws.amazon.com/cloud-map/latest/api/API_RegisterInstance.html

Fixes #4713

Checklist

• Unit tests updated
• End user documentation updated

[mloiseleur]

/ok-to-test
@mjlshen Thanks for this PR, it looks good. 🤔 Shouldn't it be added to documentation, too ?

[mjlshen]

Thanks for this PR, it looks good. 🤔 Shouldn't it be added to documentation, too ?

@mloiseleur I took a brief look, but couldn't find a good place for documenting specific providers. I could work on extending the tutorial for this provider to have an IPv6 example? https://kubernetes-sigs.github.io/external-dns/v0.14.2/tutorials/aws-sd/ or if there was a different place you had in mind?

[mloiseleur]

Since it's an update to the aws sd provider, yes, it make sense to me.

[szuecs]

code lgtm from my side

[mloiseleur]

@mjlshen would you please extend the aws sd tutorial with this information ?
After that, I think we are good to go.

[mjlshen]

Yes, sorry, I am trying, but struggling to reproduce this issue exactly. Will do once I figure it out.

[mjlshen]

@mloiseleur Ok I finally figured out a way to create AAAA records with the AWS-SD provider. The main issue I ran into was the lack of dualstack load balancer support in the AWS-SD provider when compared to the AWS provider. Currently, whenever a load balancer is detected, the AWS-SD provider only creates an A record:

external-dns/provider/awssd/aws_sd.go

Lines 488 to 493 in b834fef

	if ep.RecordType == endpoint.RecordTypeCNAME {
	if p.isAWSLoadBalancer(target) {
	attr[sdInstanceAttrAlias] = target
	} else {
	attr[sdInstanceAttrCname] = target
	}

i.e. the AWS-SD doesn't have the equivalent of #1079 yet from the AWS provider. I chose to document this gap for now instead of attempting to also fix this in the PR, though I will also file an issue to track this.

[mloiseleur]

Suggested change

	> The AWS-SD provider does not currently support dualstack loadbalancers and will only create A records for these at this time. See the AWS provider and the [AWS Load Balancer Controller Tutorial](./aws-load-balancer-controller.md) for dualstack loadbalancer support.
	```yaml
	apiVersion: v1
	kind: Service
	metadata:
	name: nginx
	annotations:
	external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com
	external-dns.alpha.kubernetes.io/ttl: "60"
	spec:
	ipFamilies:
	- "IPv6"
	type: NodePort
	ports:
	- port: 80
	name: http
	targetPort: 80
	selector:
	app: nginx
	```
	```yaml
	apiVersion: v1
	kind: Service
	metadata:
	name: nginx
	annotations:
	external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com
	external-dns.alpha.kubernetes.io/ttl: "60"
	spec:
	ipFamilies:
	- "IPv6"
	type: NodePort
	ports:
	- port: 80
	name: http
	targetPort: 80
	selector:
	app: nginx
	```
	:information_source: The AWS-SD provider does not currently support dualstack loadbalancers and will only create A records for these at this time. See the AWS provider and the [AWS Load Balancer Controller Tutorial](./aws-load-balancer-controller.md) for dualstack loadbalancer support.

[mjlshen]

Oh thanks, updated! I also changed loadbalancer --> load balancer because I realized that it should be two words :D

[mloiseleur]

I have tiny suggestion about documentation order and we are good to go.
Thanks @mjlshen 👍

[mloiseleur]

/lgtm
/approve

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