What is a Subnet in AWS and How to Change its Availability Zone?

What is a Subnet in AWS?

A subnet is a logical subdivision of an IP network into multiple, smaller network segments. Each subnet has its own unique address range and gateway. Subnets are used to improve network performance and security.

In AWS, you can create subnets in your VPCs. You can then launch instances into your subnets. When you create a subnet, you must specify the Availability Zone in which to create the subnet. AWS creates a routing table for each subnet.

How to Change the Availability Zone of Subnet in AWS?

You can change the Availability Zone of a subnet using the AWS Management Console, and the AWS Command Line and Interface (AWS CLI).

To change the Availability Zone of a subnet using the console, follow these steps:

1. Open the Amazon VPC console.
2. In the navigation pane, choose Subnets.
3. Select the subnet, and choose Actions, Change Availability Zone.
4. In the Change Availability Zone dialog box, select the new Availability Zone, and then choose Yes, Change.
5. Your subnet’s new Availability Zone is now displayed on the Subnets page.

You can change the routing table associated with a subnet at any time. For more information, see Route Tables.

When We Can’t Change the Availability Zone of Subnet?

You can’t change the Availability Zone of a subnet if it has running instances or if it’s associated with a routing table. To change the Availability Zone of a subnet, you must first disassociate it from the routing table and then detach any running instances. For more information, see Disassociating a Subnet from a Route Table and Detaching an Internet Gateway.

If you change the Availability Zone of a subnet, we recommend that you also update the network access control list (ACL) associated with the subnet. For more information, see Network ACLs.

Can We Use a Subnet in Multiple Availability Zone?

Yes, you can create a subnet in multiple Availability Zones. This is known as an “availability zone-balanced” or “AZ-balanced” subnet. When you create an AZ-balanced subnet, AWS creates the subnet in all Availability Zones that are enabled for your VPC.