publicdns2cname

What is this?

Automatically add EC2 Public DNS as a CNAME of any domain on Route53 when the instance starts.
Your hostname will be persistent, like an Elastic IP!

Why?

When an EC2 instance starts from stop state (= not reboot), global IP address and public DNS will be randomly changed unless you enabled Elastic IP on that instance.

But normally EIP is allowed to have 5 per account, so assigning them to each instance is not a best practice. This script makes it easy to access specific instance with any hostname you choose, using EC2 instance tags.

Example?

Let's say you put "web1.ec2.example.com" to "cname" tag on your instance, and you have domain "example.com" in your Route53 hosted zones. With this script, you can access to the instance by "web1.ec2.example.com" all the time. No matter how many times the instance does stop/start.

I suggest having it as a hostname. Like EC2 public DNS, internal name resolving inside VPC will be local IP, while external name resolving will stay global IP.

Requiremnents

• Runs only on Amazon Linux
• Use of AWS Route53
• awscli must be configured with route53 and ec2 privileges.
• Your EC2 instance should have "cname" tag.
• "cname" tag should have any sub-subdomain + subdomain "ec2". Example: "web.ec2.example.com"

Install

cd /etc/init.d/
curl -kOL https://raw.githubusercontent.com/lowply/publicdns2cname/master/publicdns2cname
chown root:root publicdns2cname
chmod 755 publicdns2cname
chkconfig publicdns2cname on

Credit

This is bash script + awscli re-implementation of hostname_to_route53.rb, thank you for inspiration.