When running in a public cloud environment (e.g. Oracle Cloud) PortaSIP cannot have the "real" public IP provisioned on any "local" network interface. This IP is maintained by cloud IP balancer and packets are then forwarded to internal IPs, assigned to individual cloud instances. So PortaSIP has to work using these private IPs, but being aware of the actual public IP.
Additional Info
For now let's consider Oracle Cloud as the primary "test ground".
Specifications