If a public IP was not assigned when you purchased the CVM, then there is no way to re-apply for an ordinary public IP for this CVM. However, the same function can be accomplished using EIPs. For more information on how to use this, please see Applying for EIPs.
An instance without a public IP can apply for an EIP (see the previous question) or can access the public network through NAT gateway.
NAT gateway can provide SNAT and DNAT features for CVM instances in VPCs. If you have multiple instances and want them to access the public network through the same public IP, you can use a NAT gateway.
We recommend you immediately release the EIP after it is converted from a public IP. Otherwise, the EIP that is not bound to an instance will incur IP resource fees.
You can recover public IPs that you have previously used and are not currently assigned to other users. Recovered public IPs are all EIPs. For more information, please see Retrieve the public network IP address.
Due to the limited EIP resources, you can apply for only 20 ones per account per region, and you cannot request an increased quota. CVM instances without public IPs can use NAT gateways and other methods to access the public network.
If a CVM has a public IP or EIP and its subnet is also associated with a NAT gateway (meaning the route table specifies that the next hop for the traffic of this subnet to access the public network is a NAT gateway), then the default setting is for all the traffic of this CVM to access the public network through the NAT gateway.
If you need to modify the priority so that the traffic from the CVM instance to the public network passes the public IP, please see Adjusting the Priorities of NAT Gateways and EIPs.
No, the network fee will only be charged once. When accessing the public network through public gateway or NAT gateway, only the corresponding public gateway network fee or NAT gateway network fee will be charged.