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Showing content from https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/hostname-types.html below:

Hostname types - Amazon Elastic Compute Cloud

Hostname types

AWS provides two types of hostnames: private and public. The following table compares the key differences between private and public hostnames, including how they resolve, how they're configured, and when to use each type.

​ Private hostnames Public hostnames DNS resolution Private hostnames enable private FQDNs that are not accessible from the public internet. Private hostnames only allow requests to resolve to private IPv4 and IPv6 GUA addresses within the VPC. Public hostnames enable public FQDNs that are accessible from the public internet. Public hostnames enable requests to resolve to private IPv4 and IPv6 GUA within the VPC and public IPs from the internet (split-horizon DNS). Configuration Private hostnames are configured at the instance level. Public hostnames are configured at the network interface level. When to use Public hostnames

You can use public hostnames to access EC2 instances using hostnames that resolve to the public IPv4 or IPv6 address of the instance and ease your transition to IPv6.

Public hostnames allow you to:

Public hostname types and when to use them

To use public hostnames, you have to modify an existing network interface. This section describes the three public hostname type options and helps you decide which to use:

Important

In the examples above, you can see that IP addresses are used to generate the hostname. If you change the primary private IPv4 address or the first IPv6 GUA assigned to the network interface, the portion of the hostname that translates to the IP address will change and the previously-generated public hostname will no longer be valid. In addition, changing the primary IPv4 public address forces a downstream refresh of Instance Metadata Service (IMDS) in the Amazon EC2 User Guide, so the EC2 instance IMDS metadata is automatically updated.

View public hostnames

If the VPC that the network interface is in does not have both EnableDnsHostnames and EnableDnsSupport enabled, there is no hostname type defined or generated.

Console

You can view the public hostnames for an instance or primary network interface.

To view the hostname type and DNS names of an instance

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, choose Instances.

  3. Select the checkbox for the instance.

  4. On the Network tab, under Hostname and DNS, find the following:

    • Public hostname type

    • Public DNS

    • IPv4-only IP based name

    • IPv6-only - IP based name

    • Dualstack - IP based name

To view the hostname type and DNS names of a network interface

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, choose Network Interfaces.

  3. In the search field, enter the ID of the instance. Select the ID of the network interface to open its details page.

  4. Under Hostname and DNS, find the following:

    • Public hostname type

    • Public DNS name

    • Public IPv4 DNS name

    • Public IPv6 DNS name

    • Public Dualstack DNS name

AWS CLI
To view the hostname type and DNS names of a network interface

Use the describe-network-interfaces command.

aws ec2 describe-network-interfaces \
    --network-interface-id eni-1234567890abcdef0 \
    --query NetworkInterfaces[].PublicIpDnsNameOptions

The following is example output. Because the hostname type is public-dual-stack-dns-name, the DNS hostname is the same as PublicDualStackDnsName.

[
     {
          "DnsHostnameType": "public-dual-stack-dns-name",
          "PublicIpv4DnsName": "ec2-52-54-55-66.ap-southeast-2.compute.amazonaws.com",
          "PublicIpv6DnsName": "f5lnz-0khrm-nt2u3-gyqqt-nbdl5.ap-southeast-2.ip.aws",
          "PublicDualStackDnsName": "f5lnz-0khrm-nt2u3-gyqqt-nbdl5-q3cdpO.ap-southeast-2.ip.aws"
     }
]
PowerShell
To view the hostname type and DNS names of a network interface

Use the Get-EC2NetworkInterface cmdlet.

(Get-EC2NetworkInterface `
    -NetworkInterfaceId eni-1234567890abcdef0).PublicIpDnsNameOptions

The following is example output. Because the hostname type is public-dual-stack-dns-name, the DNS hostname is the same as PublicDualStackDnsName.

DnsHostnameType        : public-dual-stack-dns-name
PublicDualStackDnsName : f5lnz-0khrm-nt2u3-gyqqt-nbdl5-q3cdpO.ap-southeast-2.ip.aws
PublicIpv4DnsName      : ec2-52-54-55-66.ap-southeast-2.compute.amazonaws.com
PublicIpv6DnsName      : f5lnz-0khrm-nt2u3-gyqqt-nbdl5.ap-southeast-2.ip.aws
Modify public hostnames types

The public hostname type options depend on the IP addresses associated with the network interface:

Prerequisites
Console
To modify the public hostname type

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, choose Network Interfaces.

  3. In the search field, enter the ID of the instance. Select the checkbox for the network interface.

    Alternatively, from the instance detail page, choose the Networking tab and select the ID of the network interface for device index 0.

  4. Choose Actions, Modify public hostname type.

  5. Choose an option:

    • Dual-stack - IP based name: A dual-stack public hostname for a network interface. Requests from within the VPC resolve to both the private IPv4 address and the IPv6 Global Unicast Address of the network interface. Requests from the internet resolve to both the public IPv4 and the IPv6 GUA address of the network interface.

    • IPv4 - IP based name: An IPv4-enabled public hostname for a network interface. Requests from within the VPC resolve to the private primary IPv4 address of the network interface. Requests from the internet resolve to the public IPv4 address of the network interface.

    • IPv6 - IP based name: An IPv6-enabled public hostname for a network interface. Requests from within the VPC or from the internet resolve to the IPv6 GUA of the network interface.

  6. Choose Modify.

AWS CLI
To modify the public hostname type

Use the modify-public-ip-dns-name-options command.

aws ec2 modify-public-ip-dns-name-options \
    --network-interface-id eni-1234567890abcdef0 \
    --hostname-type public-dual-stack-dns-name

The following is example output.

{
    "Successful": true
}
PowerShell
To modify the public hostname type

Use the Edit-EC2PublicIpDnsNameOption cmdlet.

Edit-EC2PublicIpDnsNameOption `
    -NetworkInterfaceId eni-1234567890abcdef0 `
    -HostNameType public-dual-stack-dns-name
Private hostnames

This section describes the Amazon EC2 instance private hostnames available when you launch instances into your VPC subnets.

The private hostname distinguishes the EC2 instances on your network. You may use the private hostname of an instance if, for example, you want to run scripts to communicate with some or all of the instances on your network.

Private hostname types

There are two private hostname types for the guest OS hostname when EC2 instances are launched in a VPC:

The EC2 instance guest OS hostname type depends on the subnet settings:

IP name

When you launch an EC2 instance with the Hostname type of IP name, the guest OS hostname is configured to use the private IPv4 address.

Resource name

When you launch EC2 instances in IPv6-only subnets, the Hostname type of Resource name is selected by default. When you launch an instance in IPv4-only or dual-stack (IPv4+IPv6) subnets, Resource name is an option that you can select. After you launch an instance, you can manage the hostname configuration. For more information, see Change resource based naming options for Amazon EC2.

When you launch an EC2 instance with a Hostname type of Resource name, the guest OS hostname is configured to use the EC2 instance ID.

The difference between IP name and Resource name

DNS queries for both IP names and resource names coexist to ensure backward compatibility and to allow you to migrate from IP based-naming for hostnames to resource-based naming. For private DNS hostnames based on IP names, you cannot configure whether a DNS A record query for the instance is responded to or not. DNS A record queries are always responded to irrespective of the guest OS hostname settings. In contrast, for private DNS hostnames based on resource name, you can configure whether DNS A and/or DNS AAAA queries for the instance are responded to or not. You configure the response behavior when you launch an instance or modify a subnet. For more information, see Change resource based naming options for Amazon EC2.

Where to find resource names and IP names

You can see the hostname types, resource name and IP name, in the Amazon EC2 console.

When creating an EC2 instance

When you create an EC2 instance, depending on which type of subnet you select, Hostname type of Resource name might be available or it might be selected and not be modifiable. This section explains the scenarios in which you see the hostname types resource name and IP name.

Scenario 1

You create an EC2 instance in the wizard (see Launch an EC2 instance using the launch instance wizard in the console) and, when you configure the details, you choose a subnet that you configured to be IPv6-only.

In this case, the Hostname type of Resource name is selected automatically and is not modifiable. DNS Hostname options of Enable IP name IPv4 (A record) DNS requests and Enable resource-based IPv4 (A record) DNS requests are deselected automatically and are not modifiable. Enable resource-based IPv6 (AAAA record) DNS requests is selected by default but is modifiable. If selected, DNS requests to the resource name will resolve to the IPv6 address (AAAA record) of this EC2 instance.

Scenario 2

You create an EC2 instance in the wizard (see Launch an EC2 instance using the launch instance wizard in the console) and, when you configure the details, you choose a subnet configured with an IPv4 CIDR block or both an IPv4 and IPv6 CIDR block ("dual stack").

In this case, Enable IP name IPv4 (A record) DNS requests is selected automatically and can't be changed. This means that requests to the IP name will resolve to the IPv4 address (A record) of this EC2 instance.

The options default to the configurations of the subnet, but you can modify the options for this instance depending on the subnet settings:

When viewing the details of an existing EC2 instance

You can see the hostname values for an existing EC2 instance in the Details tab for the EC2 instance:

In addition, if you connect to your EC2 instance directly over SSH and enter the hostname command, you'll see the hostname in either the IP name or resource name format.

Choosing between resource names and IP names

When you launch an EC2 instance (see Launch an EC2 instance using the launch instance wizard in the console), if you choose a Hostname type of Resource name, the EC2 instance launches with a hostname in the resource name format. In such cases, the DNS record for this EC2 instance can also point to the resource name. This gives you the flexibility to choose whether that hostname resolves to the IPv4 address, the IPv6 address, or both the IPv4 and IPv6 address of the instance. If you plan to use IPv6 in the future or if you are using dual-stack subnets today, it’s best to use a Hostname type of Resource name so that you change DNS resolution for the hostnames of your instances without making any changes to the DNS records themselves. The resource name allows you to add and remove IPv4 and IPv6 DNS resolution on an EC2 instance.

If instead you choose a Hostname type of IP name, and use it as the DNS hostname, it can only resolve to the IPv4 address of the instance. It will not resolve to the IPv6 address of the instance even if the instance has both an IPv4 address and an IPv6 address associated with it.

Change resource based naming options for Amazon EC2

You can change the hostname type and DNS hostname configurations for subnets, which affects all subsequent instance launches in that subject, or you can change them for an EC2 instances after you launch it.

Resource based naming options Subnets

Changing the subnet settings doesn't change the configuration of EC2 instances that are already launched in the subnet.

Console
To modify the options for a subnet

Open the Amazon VPC console and select the subnet. Choose Actions, Edit subnet settings. Modify the settings as needed and then save your changes.

AWS CLI
To modify the options for a subnet

Use the modify-subnet-attribute command.

aws ec2 modify-subnet-attribute \
    --subnet-id subnet-0abcdef1234567890 \
    --private-dns-hostname-type-on-launch resource-name \
    --enable-resource-name-dns-a-record-on-launch \
    --enable-resource-name-dns-aaaa-record-on-launch
PowerShell
To modify the options for a subnet

Use the Edit-EC2SubnetAttribute cmdlet.

Edit-EC2SubnetAttribute `
    -SubnetId subnet-0abcdef1234567890 `
    -PrivateDnsHostnameTypeOnLaunch ResourceName `
    -EnableResourceNameDnsAAAARecordOnLaunch $true `
    -EnableResourceNameDnsARecordOnLaunch $true
EC2 instances Considerations
Console
To modify the hostname type and DNS hostname options for an instance

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. If you're going to change the Use resource based naming as guest OS hostname setting, first stop the EC2 instance. Otherwise, skip this step.

    To stop the instance, select the instance and choose Instance state, Stop instance.

  3. Select the instance and choose Actions, Instance settings, Change resource based naming options.

    • Use resource based naming as guest OS hostname: Determines whether you want the guest OS hostname of the EC2 instance to be the resource name or IP name.

    • Answer DNS hostname IPv4 (A record) requests: Determines whether DNS requests/queries to your resource name resolve to the private IPv4 address of this EC2 instance.

    • Answer DNS hostname IPv6 (AAAA record) requests: Determines whether DNS requests/queries to your resource name resolve to the IPv6 address (AAAA record) of this EC2 instance.

  4. Choose Save.

  5. If you stopped the instance, start it again.

AWS CLI
To modify the hostname type and DNS hostname options for an instance

Use the modify-private-dns-name-options command.

aws ec2 modify-private-dns-name-options \
    --instance-id i-1234567890abcdef0 \
    --private-dns-hostname-type resource-name \
    --enable-resource-name-dns-a-record \
    --enable-resource-name-dns-aaaa-record
PowerShell
To modify the hostname type and DNS hostname options for an instance

Use the Edit-EC2PrivateDnsNameOption cmdlet.

Edit-EC2PrivateDnsNameOption `
    -InstanceId i-1234567890abcdef0 `
    -PrivateDnsHostnameType ResourceName `
    -EnableResourceNameDnsAAAARecord $true`
    -EnableResourceNameDnsARecord $true

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