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/Network path between ALB and ECS Fargate task/

Network path between ALB and ECS Fargate task


As part of a conversation about whether or not we need end to end TLS, I am trying to understand the communication path between an ALB and the ECS Fargate tasks it targets. I'm assuming the ALB and service tasks are hosted on completely distinct instances? Are these instances logically part of my VPC or not? Is the traffic confined to my VPC or does it go via AWS network's? I am arguing there is nothing to gain with TLS between ALB and services, as long as we trust AWS network, but I cannot find official document to support my argument, other than a SO thread from a AWS employee. Can anyone shed some light? Thanks

1 Answers
Accepted Answer

The traffic from ALB and your Fargate task is inside your VPC. After you deployed an ALB, you can see in the network interfaces section (in the EC2 in console) that there are some network interfaces for the ALB. Same for the task. So the traffic uses the protection of transit on a VPC.

Anyway it's highly suggested to implement TLS from ALB and your task, for a zero trust network. ALB doesn't validate the certificate from your task, this means that you can create a self signed certificate, this give you the ability to still encrypt your traffic.

The load balancer establishes TLS connections with the targets using certificates that you install on the targets. The load balancer does not validate these certificates. Therefore, you can use self-signed certificates or certificates that have expired. Because the load balancer is in a virtual private cloud (VPC), traffic between the load balancer and the targets is authenticated at the packet level, so it is not at risk of man-in-the-middle attacks or spoofing even if the certificates on the targets are not valid.

answered 4 months ago
  • Thanks, that's great. Just begs the question as to what TLS adds here, as it is, afaik, solely a mean to protect against MITM.

  • Many customers have a "encrypt everywhere" policy which is why they would deploy TLS between the ALB and the workload (Fargate in this case). They might have that policy because of internal reasons or because of legislation or industry requirements. What does it add? Eavesdropping protection on the AWS network. As Miki says - zero trust networking.

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