[ECS] [request]: Service Discovery with Public IP

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**Tell us about your request**
Support for public DNS resolving to public ip with Service Discovery.

**Which service(s) is this request for?**
ECS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
To reduce the maintenance burden, I'm trying to replace an EC2 that acts as a bastion for the VPC with a Fargate Container. However, the only way to have a reliable DNS is using a Network Load Balancer in front of the container. We run this setup on 4 different regions, which means we'd end up paying for 4 NLB with almost no gain. The alternative is to have a DNS that resolves to the container and gets automatically updated much like the ServiceDiscovery for private DNS.

**Are you currently working around this issue?**
We're currently running a sidecar container with AWS CLI that updates Route 53 with the public ip that was designated to the new Fargate instance. The sidecar shuts down after updating Route 53 and the bastion stays up and we can use the DNS for our SSH tunneling needs.