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I am trying to understand Elastic IPs pricing in AWS. There are few queries that are puzzling for me.

As per AWS Docs,

1) Limit Elastic IP addresses per region for EC2-VPC is 5. So, If i have 3 VPCs in 3 regions and connected through VPC peering. I can have 15 Elastic IPs in total for my account?

2) While your instance is running, you aren't charged for one Elastic IP address associated with the instance, but you are charged for any additional Elastic IP addresses associated with the instance.

- Does it mean, charges will be applicable for 4 Elastic IPs if I use them for the same instance? - If so, I can avoid billing for 4 elastic IPs if I use them somewhere else like, NAT, NAT Gateway, ELB, Bastion etc.?

3) We can re-assign the Elastic IPs to other instances and We can acquire new Elastic IPs from the pool. In both the cases, Won't be cached data for these IPs routed to our instances? TTL will be still alive on the client side right.

4) An Elastic IP address is accessed through the Internet gateway of a VPC. If you have set up a VPN connection between your VPC and your network, the VPN traffic traverses a virtual private gateway, not an Internet gateway, and therefore cannot access the Elastic IP address.

In here, traffic is routed through Internet Gateway. Rather than Private Gateway.

If the traffic is routed through private Gateway, can't we access bastion servers which uses elastic IPs, to administer private instances?

Please correct me if am wrong in my understanding. Thanks for your time.

AnilReddy
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1 Answers1

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  1. Yes, 5 EIPs per region means 15 EIPs for 3 regions.

  2. If you associate N EIPs to a single EC2 instance then you will be charged by the hour for N-1 of them.

  3. If you move an EIP to a new DNS name then clients that have cached your old DNS entries will need to update them.

  4. If you're connected over VPN, you would typically target private IP addresses, not public IP addresses. Your local VPN configuration would include routes to those private IPs over the VPN connection.

jarmod
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  • Yeah , I agree with you on TTL which is related to DNS resolution. Lets say I have a Route 53's record set which is routing traffic at Elastic IP of the Public subnet. DNS resolver will return elastic IP address. So, until TTL expires we will be having the old IP(elastic IP) in our cache right. – AnilReddy Aug 25 '18 at 02:56