Assign Public IP (not Elastic IP) after instance launched
Solution 1:
The instance that you launched without a public IP will stay without one as it is only assignable when you launch the instance. Even having a subnet with auto assign public IP switched on will not assign a public IP to your instance if, when you launched the instance you chose not to have a public IP.
The only way I know is to select assign a public IP before launching the instance or having the subnet set up to auto assign public IPs which will do that only when you launch a new instance.
So to summarize:
It is not possible to assign a public IP after launching that instance unless you use EIPs.
Solution 2:
To correct it afterwards, spin down your original server, spin up a new with auto assign public IP enabled and the existing volumes attached.
You can then discard the original instance.
Solution 3:
If you are using ELB and Autoscaling, creating instance on fly and to stress test the instance is difficult. One solution during this scenario:
Select EC2 instance> Actions>Networking> Manage Ip Addresses. Then use option "To add or edit an IPv4 public IP Allocate an Elastic IP to this instance or network interface".
- Create an elastic IP
- Navigate to Elastic IP address link> click Associate IP
- Select the instance to associate IP and save.
Now you will have EC2 instance with public IP without restarting/deleting EC2 instance.
Solution 4:
Assuming your instance is running in a VPC you can create an Elastic Network Interfaces (ENI) that has a public IP assigned to it then associate that ENI with your instance without needs to create a new one.