Finally, Static IP’s in EC2
I was very happy when I opened my email this morning. Amazon has announced Elastic IPs and Availability Zones. It’s time to update your EC2 tools!
The Elastic IP implementation looks good. There must be some smart engineers working at Amazon. I haven’t played with it yet, but I have some ideas on how to use it.
My first thought is NMS integration. Let’s say you were running two load balancer instances, with one in hot standby. If your NMS detects a failure, it could automatically re-assign the IP to the standby instance.
According to the docs, an instance can only have one IP address:
Can an instance have more than one Elastic IP or Public IP?
Today, an instance can only have one Internet routable IP address. If an Elastic IP is mapped to an instance its existing Public IP address mapping is removed.
If that weren’t the case, you could use RR DNS and not use a hot standby instance. This is kind of like Whackamole; you move the IP address of the failed instance to an active instance. In fact, you could probably modify Whackamole to use the EC2 API instead of ifconfig.
Reading between the lines, it looks like instances will support multiple IP addresses in the future.
In the mean time, if you need to scale for bandwidth and have failover without changing DNS, you’ll need to run N+1 and always have a hot standby. That’s still a huge improvement over depending on DNS propagation.
