Provide network connectivity for your Auto Scaling instances using Amazon VPC - Amazon EC2 Auto Scaling

Provide network connectivity for your Auto Scaling instances using Amazon VPC

Amazon Virtual Private Cloud (Amazon VPC) is a service that lets you launch AWS resources such as Auto Scaling groups in a logically isolated virtual network that you define.

A subnet in Amazon VPC is a subdivision within an Availability Zone defined by a segment of the IP address range of the VPC. Using subnets, you can group your instances based on your security and operational needs. A subnet resides entirely within the Availability Zone it was created in. You launch Auto Scaling instances within the subnets.

To enable communication between the internet and the instances in your subnets, you must create an internet gateway and attach it to your VPC. An internet gateway enables your resources within the subnets to connect to the internet through the Amazon EC2 network edge. If a subnet's traffic is routed to an internet gateway, the subnet is known as a public subnet. If a subnet's traffic is not routed to an internet gateway, the subnet is known as a private subnet. Use a public subnet for resources that must be connected to the internet, and a private subnet for resources that need not be connected to the internet. For more information about giving internet access to instances in a VPC, see Access the internet in the Amazon VPC User Guide.

Default VPC

If you created your AWS account after December 4, 2013 or you are creating your Auto Scaling group in a new AWS Region, we create a default VPC for you. Your default VPC comes with a default subnet in each Availability Zone. If you have a default VPC, your Auto Scaling group is created in the default VPC by default.

You can view your VPCs on the Your VPCs page of the Amazon VPC console.

For more information about the default VPC, see Default VPCs in the Amazon VPC User Guide.

Nondefault VPC

You can choose to create additional VPCs by going to the VPC Dashboard page in the AWS Management Console and selecting Create VPC.

For more information, see the Amazon VPC User Guide.


A VPC spans all Availability Zones in its AWS Region. When you add subnets to your VPC, choose multiple Availability Zones to ensure that the applications hosted in those subnets are highly available. An Availability Zone is one or more discrete data centers with redundant power, networking, and connectivity in an AWS Region. Availability Zones help you to make production applications highly available, fault tolerant, and scalable.

Considerations when choosing VPC subnets

Note the following considerations when choosing VPC subnets for your Auto Scaling group:

  • If you're attaching an Elastic Load Balancing load balancer to your Auto Scaling group, the instances can be launched into either public or private subnets. However, the load balancer must be created in public subnets to support DNS resolution.

  • If you're accessing your Auto Scaling instances directly through SSH, the instances can be launched into public subnets only.

  • If you're accessing no-ingress Auto Scaling instances using AWS Systems Manager Session Manager, the instances can be launched into either public or private subnets.

  • If you're using private subnets, you can allow the Auto Scaling instances to access the internet by using a public NAT gateway.

  • By default, the default subnets in a default VPC are public subnets.

IP addressing in a VPC

When you launch your Auto Scaling instances in a VPC, your instances are automatically assigned a private IP address from the CIDR range of the subnet in which the instance is launched. This enables your instances to communicate with other instances in the VPC.

You can configure a launch template or launch configuration to assign public IPv4 addresses to your instances. Assigning public IP addresses to your instances enables them to communicate with the internet or other AWS services.

When you launch instances into a subnet that is configured to automatically assign IPv6 addresses, they receive both IPv4 and IPv6 addresses. Otherwise, they receive only IPv4 addresses. For more information, see IPv6 addresses in the Amazon EC2 User Guide.

For information on specifying CIDR ranges for your VPC or subnet, see the Amazon VPC User Guide.

Amazon EC2 Auto Scaling can automatically assign additional private IP addresses on instance launch when you use a launch template that specifies additional network interfaces. Each network interface is assigned a single private IP address from the CIDR range of the subnet in which the instance is launched. In this case, the system can no longer auto-assign a public IPv4 address to the primary network interface. You will not be able to connect to your instances over a public IPv4 address unless you associate available Elastic IP addresses to the Auto Scaling instances.

Network interfaces in a VPC

Each instance in your VPC has a default network interface (the primary network interface). You cannot detach a primary network interface from an instance. You can create and attach an additional network interface to any instance in your VPC. The number of network interfaces you can attach varies by instance type.

When launching an instance using a launch template, you can specify additional network interfaces. However, launching an Auto Scaling instance with multiple network interfaces automatically creates each interface in the same subnet as the instance. This is because Amazon EC2 Auto Scaling ignores the subnets defined in the launch template in favor of what is specified in the Auto Scaling group. For more information, see Creating a launch template for an Auto Scaling group.

If you create or attach two or more network interfaces from the same subnet to an instance, you might encounter networking issues such as asymmetric routing, especially on instances using a variant of non-Amazon Linux. If you need this type of configuration, you must configure the secondary network interface within the OS. For an example, see How can I make my secondary network interface work in my Ubuntu EC2 instance? in the AWS Knowledge Center.

Instance placement tenancy

By default, all instances in the VPC run as shared tenancy instances. Amazon EC2 Auto Scaling also supports Dedicated Instances and Dedicated Hosts. For more information, see Create a launch template using advanced settings.

AWS Outposts

AWS Outposts extends an Amazon VPC from an AWS Region to an Outpost with the VPC components that are accessible in the Region, including internet gateways, virtual private gateways, Amazon VPC Transit Gateways, and VPC endpoints. An Outpost is homed to an Availability Zone in the Region and is an extension of that Availability Zone that you can use for resiliency.

For more information, see the AWS Outposts User Guide.

For an example of how to deploy an Auto Scaling group that serves traffic from an Application Load Balancer within an Outpost, see the following blog post Configuring an Application Load Balancer on AWS Outposts.

More resources for learning about VPCs

Use the following topics to learn more about VPCs and subnets.