Elastic Compute Service:Primary private IP address

Background information

• Upon creation, an ECS instance is equipped with a default ENI, known as the primary ENI. This primary ENI receives a primary private IPv4 address from the IPv4 CIDR block of the vSwitch, which functions as the default egress private IP address.

• Secondary ENIs, similar to the primary ENI, receive a default primary private IPv4 address that cannot be unassociated from the ENI.

• If you want more IP addresses in addition to the primary private one, you can add secondary private IP addresses to the primary ENI or introduce more secondary ENIs to your ECS instance. The figure below illustrates the relationship between ECS instance ENIs and private IP addresses:

Procedure

1. Log on to the ECS instance buy page.

2. On the Custom Launch tab, in the Network and Zone section, select an existing virtual private cloud (VPC) and an existing vSwitch, or click Create VPC and Create vSwitch to create a VPC and a vSwitch in the VPC console, respectively. After both are created, refresh the ECS instance buy page for the updated VPC list and vSwitch list by clicking the icon.

3. Select Specify Primary Private IP Address of Primary ENI and set a primary private IPv4 address for the ECS instance.

   

Procedure

1. Log on to the ECS console.

2. In the left-side navigation pane, choose Instances & Images > Instances.

3. In the top navigation bar, select the region and resource group to which the resource belongs.

4. Find the ECS instance that you want to manage. In the Actions column, select > Network and Security Group > Modify Private IP Address.

5. In the Modify Private IP Address dialog box, configure the parameters and click OK.

   • Before changing the vSwitch, ensure the new vSwitch is in the same zone as the ECS instance.

   • If not changing the vSwitch, directly modify the primary private IP address. If the primary private IP address is left blank, the system automatically assigns a new primary private IP address.

   • To use a vSwitch that is in a different zone from your ECS instance, you must migrate your ECS instance to the zone of the vSwitch. For more information, see Change instance types across zones.

6. In the Actions column of the ECS instance that you want to manage, select > Instance Status > Start. The new primary private IP address is effective after the ECS instance restarts.

7. (Optional) After changing the primary private IP address, you may need to update the security group rules for your ECS instance to reflect the new IP address. For more information, see Modify a security group rule.

Primary private IP address of a secondary ENI

You can use one of the following methods to create a secondary ENI:

• Create a secondary ENI alongside the ECS instance creation

  When creating an ECS instance, you have the option to include an ENI that is automatically assigned a primary private IPv4 address and is associated with the ECS instance, without needing additional steps. You can associate up to two ENIs to an ECS instance: one primary (associated automatically) and one secondary. Note that you cannot specify the primary private IP address for a secondary ENI created in this manner.

• Create a secondary ENI separately

  Create ENIs separately on the Network & Security > Elastic Network Interfaces page. These ENIs can be associated with an ECS instance as secondary ENIs. You can specify the primary private IPv4 address for them during creation, provided that the IP address is an idle IP address within the IPv4 CIDR block of the vSwitch. If not specified, an idle private IPv4 address is automatically assigned to such an ENI upon creation. For more information, see Create a secondary ENI.