How to find the IP address of an amazon EC2 instance on reboot

Question

On reboot, the IP address of an amazon instance changes. How to find the new IP address using java API?

Answer 1

The public IPv4 address is also available from the EC2 instance like so:

curl checkip.amazonaws.com

And the public hostname is:

dig -x $(curl -s checkip.amazonaws.com) +short

Answer 2

On reboot, the IP addresses of an EC2 instance do not change. They do generally change on stop/start of a non-VPC EBS boot instance.

See my answer to your related question here:

https://stackoverflow.com/questions/7533871/difference-between-rebooting-and-stop-starting-an-amazon-ec2-instance

That said, you can find the private and public IP addresses through the API call for DescribeInstances in your particular language.

If you are on the instance itself, you can also find the IP addresses through the user-data API using simple HTTP:

http://instance-data/latest/meta-data/local-ipv4
http://instance-data/latest/meta-data/public-ipv4

For example,

wget -qO- http://instance-data/latest/meta-data/public-ipv4

Elastic IP addresses are recommended for keeping a consistent (static) externally facing IP address for a particular service or server. These need to be re-assigned to an instance after a stop/start (but not after a reboot).

Answer 3

You can use CLI CRUD aplication to AWS resources. AWS-CRUD-Manager

To find all ec2 instances

./awsconsole.py ec2 all

To find all of data for one ec2 instances (including IP priv and public)

./awsconsole.py ec2 find -i <id-insta`ce>

Answer 4

this is how I did it on an Ubuntu 12.04 EC2 instance within a VPC:

curl ifconfig.me

not sure why but public-ipv4 was not found under the meta-data url

Answer 5

you Can Use This.

                var ipofnewServer = string.Empty;    
                while (string.IsNullOrEmpty(ipofnewServer))
                {
                    var statusRequest1 = new DescribeInstancesRequest
                    {
                        InstanceIds = new List<string>() { instanceId }
                    };

                    var result = amazonEc2client.DescribeInstances(statusRequest1);
                    var status = result.Reservations[0].Instances.FirstOrDefault();
                    if (status != null)
                    {
                        ipofnewServer = status.PublicIpAddress;
                    }
                }

Answer 6

Assuming your rebooting the instance and not launching from scratch than you can assign an elastic IP which always remains with the ec2 instance(unless you move the IP to another server). This allows you to point all your DNS to that one IP and not worry that a reboot will cause you issues.

I think thats what your asking but there are other things you could be asking. The internal IP of the server changes(if you relaunch the instance not reboot) and you can't 'reserve' it so you may need to create a script to keep you the new IP(if your pointing internal services to it).

hope that helps