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According to the AWS docs it is possible to setup HA between two EC2 instances, however I would like to use only a single EIP.

If you scroll down the page to the section related to elastic ips, the tutorial mentions that we will need 3 EIPs. I am configuring each NAT instance to reside in a different availability zone, but within the same VPC. With this config I should only need 1 EIP as the VIP, then use internal IPs to facilitate communication between NAT-1 and NAT-2 correct? Using 3 EIPs in this situation seems like overkill.

Goal is to be able to ssh to gateway.sn3.domain.com (via single EIP) and gain access even if the primary NAT (NAT-1) is down.

--Update--

Looks like I may have to but an ELB in front of the NATs in order to support this.

aws ec2 elastic ip to multiple instance

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    ELB won't help you on a NAT instance. It's a layer 4/7 service, only for delivering inbound TCP connections to a pool of instances on specific configured ports. But, there'a this: docs.aws.amazon.com/AWSEC2/latest/UserGuide/… ... as a side note, I just upgraded a NAT instance today that had been working for 35 months with no intervention. – Michael - sqlbot Oct 13 '15 at 22:56
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According to the AWS notes:

Note: Because the set of IP addresses associated with a LoadBalancer can change over time, you should never create an "A" record with any specific IP address. If you want to use a friendly DNS name for your load balancer instead of the name generated by the Elastic Load Balancing service, you should create a CNAME record for the LoadBalancer DNS name, or use Amazon Route 53 to create a hosted zone. For more information, see Using Domain Names With Elastic Load Balancing.

So I did what they recommended, and it works great! I did notice that under-the-hood they associated two public IPS as they are visible when I dig the dns entry, but via the AWS console, the instances associated to the loadbalancer do NOT have public ips.

Setup ended up like this:

CNAME    gateway.sn3.example.com   lb-nat.somecrazy-dns-entry-aws-creates

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