You can't keep the public IP address for a production app after a failover. When you bring up a workload as part of the failover process, you need to assign an Azure public IP address resource to it. The resource must be available in the target region. You can assign the Azure public IP address resource manually, or you can automate it with a recovery plan. By default, when you enable disaster recovery for Azure VMs, Site Recovery creates target resources based on source resource settings. For Azure VMs configured with static IP addresses, Site Recovery tries to provision the same IP address for the target VM, if it's not in use.