Change Instance type impact on ENI

No, changing an EC2 instance's instance type, family, or size has no effect on the Elastic Network Interface (ENI) associated with it. The ENI's private IP address and MAC address will remain unchanged after the instance type is changed.

When the instance type of an existing instance is changed, the instance is stopped, the new instance type is applied, and the instance is restarted. The ENI retains its configuration, including private IP addresses, MAC addresses, and any associated security groups, during this process.

It should be noted, however, that the number of ENIs and private IP addresses that can be assigned to an instance varies depending on the instance type. To avoid potential issues, ensure that the new instance type you select supports the same or more ENIs and private IP addresses than the current instance type.

You can find the instance type limits in the Amazon EC2 documentation https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html#AvailableIpPerENI

Hi,

when you change the instance family or size the ENI will not be changed. The IP private IP adress will stay the same on the ENI. The MAC address also stays the same in my scenarios, but the behavior is not officially documented so it could change under certain circumstances (e.g. when moving from Nitro to Xen based instances).

There is potential impact when you have multiple ENIs attached to an instance and you try to size it smaller to a degree where the number of ENIs are not supported anymore. In this case you have to remove ENIs first before proceeding.