ec2: implement IPeer to PrefixList

[Tietew]

Describe the feature

When we want to add a security group rule which peer is a PrefixList,
we should write following code:

const pl = new ec2.PrefixList(this, 'PrefixList', { ... });
instance.connections.allowFrom(ec2.Peer.prefixListId(pl.prefixListId), ec2.Port.XXX);

It's a bit frustrated with the redundant prefixListId.

Use Case

We want to write DRY:

const pl = new ec2.PrefixList(this, 'PrefixList', { ... });
instance.connections.allowFrom(pl, ec2.Port.XXX);

Proposed Solution

• Update IPrefixList to extend IPeer
• Update PrefixListBase to implement IPeer

Other Information

Related to #33606
We can rewrite its example simpler:

const plCloudFront = ec2.PrefixList.fromLookup(this, 'CloudFrontPrefixList', {
  prefixListName: 'com.amazonaws.global.cloudfront.origin-facing',
});
alb.connections.allowFrom(plCloudFront, ec2.Port.HTTPS);

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

2.180.0

Environment details (OS name and version, etc.)

N/A

[pahud]

Hi @Tietew, thanks for the feature request!

This is a great suggestion to improve the developer experience when working with prefix lists in security group rules. Having PrefixList implement IPeer would be a natural extension that makes the API more intuitive and reduces redundancy.

Your proposed approach makes sense:

1. Update IPrefixList to extend IPeer
2. Update PrefixListBase to implement IPeer

This would be a non-breaking change that adds functionality while maintaining backward compatibility. Since you've indicated you might be able to implement this feature, we'd be happy to review a PR for this enhancement.

When implementing, you'd want to:

1. Modify the IPrefixList interface to extend IPeer
2. Implement the required IPeer methods in PrefixListBase (or a mixin if that's more appropriate)
3. Add appropriate tests to verify the new functionality works as expected

This would pair well with your other suggestion in #33606 for PrefixList.fromLookup(), allowing for a much cleaner API when working with prefix lists in security groups.

We'll review your PR when it's ready.