AWS Static IP Address
EC2 and IP Addresses
One of the things that takes a little getting used to in AWS, or any cloud infrastructure really, is setting servers to use DCHP. We, as systems administrators, have been beating into the mantra that servers always need static addresses. For those who are managing their cloud IaaS where EC2s are disposable cogs, then congratulations. You are using it as intended. But, for the rest of us whose IaaS resembles our legacy on prem datacenters, then we need to care about the infrastructure as we always have. That includes the fact that our server IP address cannot change.
Much like EC2 MAC addresses that I mentioned in a previous post, EC2 IP addresses work in a similar manner. The Elastic Network Interface (ENI) on an EC2 instance will retain it’s MAC address and private IP address throughout the life of that instance. Though it is set as dynamic (DHCP) it will behave like it is a static IP address.
When you automatically assign a public IP at instance initiation, that address is subject to change at start and stop. In fact, I have never seen a time when it didn’t change. The way to combat that is the assign an Elastic IP address (EIP). AWS doesn’t charge you for the first EIP on an instance when that address is in use but will charge you $.005/ hour to park it unused.
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