How can I get a fixed public IPv4 address for my instance?

The public IP address of your instance changes every time you stop or start it. To prevent this and get a fixed IP, you can associate an EIP to the instance that you make persistent using the osc.fcu.eip.auto-attach tag. That way, every time you stop or start the instance, the same EIP is associated with it. 

To associate the EIP to the instance, you can use the External IPs tab in Cockpit, or the AWS CLI. For more information, see External IP Addresses (EIPs).

You can then add the tag to the instance in the user data, or using a regular tag (with osc.fcu.eip.auto-attach as Key and your EIP as Value). For more information, see Configuring an Instance with User Data and 3DS OUTSCALE Tags or Tagging Your Resources.