ELB - Dualstack without public IPv4 - clarifcation needed

Yes, you can use the new dual-stack without public IPv4 feature for Application Load Balancers (ALBs) while still maintaining compatibility with AWS services that don't yet support IPv6, such as Amazon SES or Amazon Aurora.

When you configure an ALB to use dual-stack without public IPv4, it affects how internet clients connect to your load balancer, but it doesn't change how your EC2 instances communicate with other AWS services within your VPC.

Here's how it works:

1. The ALB will only have IPv6 addresses for internet-facing connections. This means clients connecting from the internet will use IPv6 to reach your application.

2. However, the communication between the ALB and your EC2 instances (the targets) remains dual-stack. This means your EC2 instances can still use both IPv4 and IPv6 for internal communications.

3. Your EC2 instances, being dual-stack, can continue to communicate with other AWS services using IPv4 as needed. This includes services like Amazon SES and Amazon Aurora that currently don't support IPv6.

So, by using this new ALB feature, you can potentially reduce IPv4-related costs for your internet-facing traffic while maintaining compatibility with AWS services that still rely on IPv4 internally.

It's important to note that this setup provides flexibility in your network architecture. You can have IPv6-only clients connecting to your application through the ALB, while your backend services and internal AWS service communications continue to use IPv4 as needed.

Remember to ensure that your VPC and subnet configurations support both IPv4 and IPv6 to fully leverage this dual-stack capability.

Sources
AWS Weekly Roundup: Application Load Balancer IPv6, Amazon S3 pricing update, Amazon EC2 Flex instances, and more (May 20, 2024) | AWS News Blog
What is an Application Load Balancer? - Elastic Load Balancing

Hi Spaceversa

Activating dual-stack for your Application Load Balancer (ALB) allows it to handle both IPv4 and IPv6 traffic, but services like AWS SES and Aurora (without IPv6 support) could face issues.

Troubleshooting Steps:

• Check Target Group Health: Ensure EC2 instances are healthy.
• Verify Security Groups: Confirm rules allow traffic from the ALB on necessary ports for both IPv4 and IPv6.
• DNS Configuration: Ensure A (IPv4) and AAAA (IPv6) records are correctly set up.
• Application Configuration: Check that your application can interact with AWS services using IPv4.