Elastic Compute Service:IP addresses of ECS instances in the classic network

Each ECS instance in the classic network is assigned an internal IP address for communication over the internal network.

Internal IP addresses can be used in the following scenarios:

• Load balancing

• Communication over the internal network between ECS instances within the same LAN

• Communication over the internal network between an ECS instance and other cloud services, such as Object Storage Service (OSS) and ApsaraDB RDS, within the same LAN

Public IP addresses can be used in the following scenarios:

• Communication between ECS instances and the Internet

• Communication between an ECS instance and other cloud services that are not within the same LAN

The following section describes the operations related to public IP addresses:

• If you select Assign Public IP Address when you create an ECS instance in the classic network, the system assigns a public IP address to the instance. For more information, see Create an instance on the Custom Launch tab.

  Note

  After the system assigns a public IP address to an ECS instance in the classic network, you cannot release or disassociate the public IP address. If you set the public bandwidth of an instance to 0 Mbit/s when you downgrade the configurations of the instance during renewal or change the bandwidth of a pay-as-you-go instance, the instance cannot connect to the Internet but the public IP address is retained.

• If you do not select Assign Public IP Address when you create an ECS instance in the classic network, you can assign a public IP address to the instance by modifying the outbound public bandwidth. For information about how to modify the public bandwidth of a subscription ECS instance, see Modify the bandwidth configurations of subscription instances. For information about how to modify the public bandwidth of a pay-as-you-go ECS instance, see Modify the bandwidth configurations of pay-as-you-go instances.

• You can modify the public IP address of an instance only within six hours after the instance is created. For more information, see Change the public IP address of an instance.

• When you manually release an ECS instance in the classic network, you can convert the public IP address of the instance into an elastic IP address (EIP). You can associate EIPs with ECS instances in virtual private clouds (VPCs) in various scenarios, such as network migration and flexible bandwidth adjustment. For more information, see Convert the system-assigned public IP address of an instance in the classic network into an EIP.